Skip to main content


Don't feel bad if you are confused. You are in good company. No one really understands it.
If these terms confuse you, this diary is for you. These terms are often found in astronomy news stories. No doubt, many wonder what astronomers mean when they use these expressions. I hope to clarify them enough so you can feel like you have a better basic understanding of what in the world they are saying.

This is not a highly technical treatment of dark matter and dark energy. There are many Kos readers who know a lot about these topics. I hope they add helpful comments. This diary is for the Kos readers who feel they don't know much about them. They want a little more information. When astronomers finally do report they know the nature of dark matter and dark energy, the story will have more significance.

More below the squiggle.

What Can Be Seen and Detected?
The Universe is a big place. You have seen it with your own eyes on a clear night with good seeing conditions away from light pollution. You have seen it in the millions of wonderful images from ground based telescopes and those in space. Most people are very familiar with the Hubble Space Telescope images. You can browse for the rest of your life at this one site alone. Here is a recent image of a portion of the Carina Nebula.


The historic view below (click for a much bigger image) is actually a composite of images taken by Hubble's Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS). It took 400 orbits to make the observations. The Hubble telescope's Advanced Camera for Surveys' wide-field camera snapped 800 exposures, which equals two exposures per orbit. The exposures were taken over four months, from Sept. 24, 2003 to Jan. 16, 2004. The 800 exposures amounted to about 1 million seconds or 11.3 days of viewing time. The average exposure time was 21 minutes. The observations were taken in visible to near-infrared light. Astronomers compare the Ultra Deep Field view to looking through an eight-foot-long soda straw. Astronomers would need about 50 Ultra Deep Fields to cover the entire Moon. Hubble's keen vision (0.085 arc seconds.) is equivalent to standing at the U.S. Capitol and seeing the date on a quarter a mile away at the Washington monument. More details here.

A key question for astronomers is whether the universe appears to be the same at this very early time as it did when the cosmos was between 1 and 2 billion years old.


The Hubble Ultra Deep Field (HUDF) field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion.

The final ACS image, assembled by Anton Koekemoer of the Space Telescope Science Institute, is studded with a wide range of galaxies of various sizes, shapes, and colors. In vibrant contrast to the image's rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge.

What we are seeing in these images is made of the the matter we can detect with cameras, our eyes, telescopes, etc. This matter makes up less than 5% of the universe.

The Case for Dark Matter
The evidence for matter which we cannot see is simple if you consider the physics which infers its presence. Galaxies are known to rotate. If you are on a rotating merry-go-round, you need to lean inward as you move in order to create a small centrally directed force on your body. This inward force keeps you from going in a straight line tangentially off the edge of the ride. The faster the ride, the greater the force needed. In the galactic merry-go-round, this force is the pull of gravity. The central bulge of the galaxy is very massive. It attracts the smaller massed stars that make up the disc keeping them in rotation around the galaxy.

In the 1970s, Vera Rubin made careful observations of galaxy rotation rates. Rubin and Kent Ford began making Doppler observations of the orbital speeds in spiral galaxies. Their results were quite surprising.

The stars far from the centers of galaxies, in the sparsely populated outer regions, were moving just as fast as those closer in. This was odd, because the visible mass of a galaxy does not have enough gravity to hold such rapidly moving stars in orbit. It followed that there had to be a tremendous amount of unseen matter in the outer regions of galaxies where the visible stars are relatively few. Rubin and Ford went on to study some sixty spiral galaxies and always found the same thing. “What you see in a spiral galaxy,” Rubin concluded, “is not what you get.”

"In a spiral galaxy, the ratio of dark-to-light matter is about a factor of ten. That's probably a good number for the ratio of our ignorance-to-knowledge. We're out of kindergarten, but only in about third grade." —Vera Rubin

Her calculations showed that galaxies must contain about ten times as much “dark” mass as can be seen in visible stars. Ninety percent of the mass in galaxies is invisible and unidentified.

Additional studies of clusters, or groupings, of galaxies support this conclusion.
Here is a link to a helpful article by Martin Rees, Astronomer Royal and Professor of Cosmology and Astrophysics at the University of Cambridge on the subject of Dark Matter.

The Case for Dark Energy

Evidence for dark energy comes from supernova studies in the 1990s. The Hubble Space Telescope and detector developments allowed astronomers to study supernovae at much farther distances than before. Type 1a supernovae have a very uniform behavior when their light output is studied. They brighten quickly, then more gradually decrease in brightness over time. This behavior allows astronomers to use them as a sort of standard brightness candle. By observing how bright it appears and comparing to how bright 1a supernovae are at closer known distances, one can calculate the distance to the farther one.

Hubble's Law of the Expanding Universe tell us that farther things are moving away from us at faster speeds due to the Big Bang. The supernova studies in the 1990s showed that the far distant points in space are actually farther than Hubble's Law predicts. Space is expanding at an increasing, or accelerating rate.

About 72% of the Universe is in a form of mass and energy capable of creating that acceleration. It is not known what it is.

Here is a link to a recent excellent diary by palantir on the awarding of the 2011 Nobel Prize in Physics for this supernova work.
Here is a link to a helpful article by John D. Barrow, cosmologist and Professor of Mathematical Sciences at the University of Cambridge on the subject of Dark Energy.

Time Line of the Universe
Below is a graphic of the growth and change of the universe over 13.7 billion years from the Wilkinson Microwave Anisotropy Probe (WMAP) mission. The far left depicts the earliest moment we can study. A period of "inflation" produced a burst of exponential growth in the universe. The vertical scale represents the size of the universe. For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The graphic shows this effect as the shape grows increasingly wider at the right end. This is the accelerating expansion due to dark energy discovered from supernova studies in the 1990s.


I hope this brief summary of Dark Matter and Dark Energy is helpful. Much is being learned by the astronomy community about these topics with more research. And, there are hopes that the experiments at the CERN Large Hadron Collider will yield new insights. Some day it is hoped we will finally know what makes up the other 95% of the universe.

The Fabric of the Cosmos on PBS NOVA
"The Fabric of the Cosmos," a four-hour series based on the book by renowned physicist and author Brian Greene, takes us to the frontiers of physics to see how scientists are piecing together the most complete picture yet of space, time, and the universe. The first episode was Nov. 2 at 9 Eastern. Episodes 2, 3, and 4 are scheduled for Nov. 9, 16, and 23. Episodes can be viewed online after they air.

Originally posted to SciTech on Tue Nov 08, 2011 at 08:10 AM PST.

Also republished by Community Spotlight.

Your Email has been sent.
You must add at least one tag to this diary before publishing it.

Add keywords that describe this diary. Separate multiple keywords with commas.
Tagging tips - Search For Tags - Browse For Tags


More Tagging tips:

A tag is a way to search for this diary. If someone is searching for "Barack Obama," is this a diary they'd be trying to find?

Use a person's full name, without any title. Senator Obama may become President Obama, and Michelle Obama might run for office.

If your diary covers an election or elected official, use election tags, which are generally the state abbreviation followed by the office. CA-01 is the first district House seat. CA-Sen covers both senate races. NY-GOV covers the New York governor's race.

Tags do not compound: that is, "education reform" is a completely different tag from "education". A tag like "reform" alone is probably not meaningful.

Consider if one or more of these tags fits your diary: Civil Rights, Community, Congress, Culture, Economy, Education, Elections, Energy, Environment, Health Care, International, Labor, Law, Media, Meta, National Security, Science, Transportation, or White House. If your diary is specific to a state, consider adding the state (California, Texas, etc). Keep in mind, though, that there are many wonderful and important diaries that don't fit in any of these tags. Don't worry if yours doesn't.

You can add a private note to this diary when hotlisting it:
Are you sure you want to remove this diary from your hotlist?
Are you sure you want to remove your recommendation? You can only recommend a diary once, so you will not be able to re-recommend it afterwards.
Rescue this diary, and add a note:
Are you sure you want to remove this diary from Rescue?
Choose where to republish this diary. The diary will be added to the queue for that group. Publish it from the queue to make it appear.

You must be a member of a group to use this feature.

Add a quick update to your diary without changing the diary itself:
Are you sure you want to remove this diary?
(The diary will be removed from the site and returned to your drafts for further editing.)
(The diary will be removed.)
Are you sure you want to save these changes to the published diary?

Comment Preferences

  •  Thank you very much! (20+ / 0-)

    There are moments when the body is as numinous as words, days that are the good flesh continuing. -- Robert Hass

    by srkp23 on Tue Nov 08, 2011 at 08:16:50 AM PST

  •  Great diary. (14+ / 0-)

    Thank you.

    This comment may not be reproduced or excerpted on other sites without my express written permission.

    by psilocynic on Tue Nov 08, 2011 at 08:27:53 AM PST

  •  Has anyone ever considered that (10+ / 0-)

    gravity may have a kind of exponential effect?

    This comment may not be reproduced or excerpted on other sites without my express written permission.

    by psilocynic on Tue Nov 08, 2011 at 08:30:02 AM PST

    •  I have never read anything about it. (15+ / 0-)

      I think it is a very well understood force in the context of today's universe. How it behaved in the early moments, or before the Big Bang, is another story. There are some who theorize about quantum effects with gravity. If you get a chance, watch the NOVA shows. Brian Greene will probably talk about some of those theories.

      Thanks for your question.

    •  We lack a good theory of gravity, and (14+ / 0-)

      especially a quantum theory of gravity or theory of quantum gravity. Some have hypothesized that the effect of gravity could be different at different scales. This would mean that the old empirically derived "rule of thumb" equation of:

      G = Mm/r^2 would need some twiddling. Specifically, it would need twiddling in the denominator beyond those needed for relativistic effects that would introduce either a step-wise break or some other weird function (inverse hyperbolic?).

      So far nobody has proposed any such actual modified equation that maps as well onto the data as Einstein's use of the fudge factor ω.

      That, in its essence, is fascism--ownership of government by an individual, by a group, or by any other controlling private power. -- Franklin D. Roosevelt --

      by enhydra lutris on Tue Nov 08, 2011 at 09:18:05 AM PST

      [ Parent ]

      •  Einstein called it a fudge factor, but if he was (7+ / 0-)

        working now he would have included it as a free parameter.

        However, the cosmological constant having a nonzero value is what "dark energy" means.

        Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

        by eigenlambda on Tue Nov 08, 2011 at 01:39:34 PM PST

        [ Parent ]

        •  Modified Newtonian dynamics. (0+ / 0-)

          As I (a curious non-scientist) understand it, MOND theory essentially says gravity works a bit differently over long distances than at short ones. A 2006 study of colliding galaxies was initially claimed to disprove MOND, but MOND proponents have tweaked the theory a bit to compensate. But still, if I'm following this correctly, MOND theory cannot account for all observable phenomena. But of course, neither can any other theory.

          "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

          by HeyMikey on Wed Nov 09, 2011 at 08:11:22 AM PST

          [ Parent ]

          •  MOND mostly died at the end of 2006 when the (0+ / 0-)

            observations of gravitational lensing in the Bullet Cluster showed gravity not pointing at normal matter.  No one thinks gravity should be modified to not point at matter, so, that was fairly conclusive evidence for dark matter.

            Here's a nice link about why you should believe in dark matter:

            Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

            by eigenlambda on Wed Nov 09, 2011 at 04:30:38 PM PST

            [ Parent ]

    •  take this with a big grain of salt (6+ / 0-)

      re: gravity

      I just read a fun book from a non-physicist.  His thought experiment is that, just as Einstein mentioned mass, gravity, curved space, and acceleration in the same breath, it actually should be viewed in reverse.  When you accelerate, say in the car, you are pressed back into your seat.  He argued this is in fact a small amount of gravity being created in your wake.  His argument is that it is the acceleration of matter that 'curves' space and creates mass and gravity.

      Anyway, it was a fun way to turn everything upside down and look at it through a different lens.  He speculates on dark energy and the expansion of space but I won't give a spoiler for the ending.

      ...the train's got its brakes on and the whistle is screaming.

      by themank on Tue Nov 08, 2011 at 11:21:16 AM PST

      [ Parent ]

      •  Umm... (10+ / 0-)

        That's an inertial effect. Mass @ rest tends to remain @ rest.

        I argue that it's a safety conscious gnome that lives in my car seat- He acts as a sort of second seat belt by grabbing my back and pulling me into the seat when I accelerate.

        My scenario is at least mathmatically possible.

      •  Snipped from Wiki because I'm lazy (6+ / 0-)

        But the equivalence of gravity and acceleration was one of the cornerstones of Einstein's General Theory of Relativity.

        A person in a free-falling elevator experiences weightlessness, and objects either float motionless or drift at constant speed. Since everything in the elevator is falling together, no gravitational effect can be observed. In this way, the experiences of an observer in free fall are indistinguishable from those of an observer in deep space, far from any significant source of gravity. Such observers are the privileged ("inertial") observers Einstein described in his theory of special relativity: observers for whom light travels along straight lines at constant speed.[3]

        Einstein hypothesized that the similar experiences of weightless observers and inertial observers in special relativity represented a fundamental property of gravity, and he made this the cornerstone of his theory of general relativity, formalized in his equivalence principle. Roughly speaking, the principle states that a person in a free-falling elevator cannot tell that he is in free fall. Every experiment in such a free-falling environment has the same results as it would for an observer at rest or moving uniformly in deep space, far from all sources of gravity.[4]
        [edit] Gravity and acceleration

        So your friend is very observant. But he's going to have to get out of bed a little earlier to get the jump on where Einstein was in 1912.

        •  hah (2+ / 0-)
          Recommended by:
          psilocynic, jim in IA

          this is why we use fall towers when we dont have the monez to go to space. My beloved and long missed hometown of Bremen has one. They test microgravity there. I always found that was a clever invention.

        •  again, grain of salt (5+ / 0-)

          while the author is not my friend he is quite familiar with Einstein and the equivalence principle.

          And I am familiar with Feynman's admonition about Cargo Cult Science.

          ...ok, a very rough synopsis of the book.  

          He plays a little thought game.  What if...  Einstein was right.  But what if space has a form of potential energy that is related to Feynman's 'sum over paths' concept.  And what if acceleration through space actually reduces that 'potential' energy of the space that is traveled through by reducing the number of possible configurations in that space due to the collapse of the wave function in the space traveled through.  What if we currently have the cart before the horse in describing acceleration and gravity.  Would things look differently if we said acceleration curves space behind and creates gravity rather than gravity curves space and makes acceleration.

          Yes; it's a lot of what if's.  But it beats watching the Republicans debate.  I don't claim to 'believe' his hypothesis, but I found it an entertaining inversion of my thinking.

          ...the train's got its brakes on and the whistle is screaming.

          by themank on Tue Nov 08, 2011 at 01:49:11 PM PST

          [ Parent ]

      •  I thought this too once (0+ / 0-)

        and then thought that it wasn't just the acceleration but the velocity of matter.  then saw that really it was a narrowing of the potential field of existence of the particle.  Since increased velocity narrowed the field of potential existence in between "pops" (re-integration from the dark-energy field on the order of 10^-32s  -- see "gravity well" post below)  By reducing the probability of existence of the particle toward a line of movement the tightening of the potential field along this line created mass and slowed time.

        taken to the extreme, this theory then shows that a singularity is simply a point in the quantum field where the potentiality of existence is only one potential state -- a full contraction of the potential field into our own space-time with no disassociation in to the quantum field of potentiality allowed -- no other potential state of existence but what is right now.


    •  what do you mean by exponential effect? (0+ / 0-)

      Please elaborate.

      Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

      by eigenlambda on Tue Nov 08, 2011 at 01:36:19 PM PST

      [ Parent ]

    •  Reply from a cosmologist (17+ / 0-)

      What you're proposing (in more general terms) is essentially that gravity does not behave as we expect it to, and that is what is causing this discrepancies. This is a hypothesis that has been examined for the past decades, and is called MOND (Modified Newtonian Dynamics.)

      Essentially, there are a few main problems with this:
      - Our picture of gravity as it is right now (general relativity) gives a very very good fit for all the data. Dark matter behaves exactly as normal matter in that aspect ,and dark energy behaves essentially like a cosmological constant (if you have had any calculus, think of it as a constant of integration) - in short the data fits the current models very well. We just don't know what this dark matter and dark energy is - we know how it behaves.

      - Two. We can 'see' dark matter through its effect on the rest of the universe. There's a process known as gravitational lensing, which allows us to visualize mass concentrations - which are often very different from the luminosity concentrations (e.g. if you look at a cluster, where the mass is is very different from where the light is - most of the mass does not emit light - 'dark matter!') MOND has not come up with any reasonable explanations for these phenomenon as of yet.

      Hope that helps (and wasn't too technical)

  •  I love this stuff. Thx! If only I could (19+ / 0-)

    have done the math, I would've been a physicist.  Instead, I'm a lawyer.  Oh well.

    I really get dark matter.  Dark energy, on the other hand, is really really weird, and, it seems, that's about the extent of the current understanding that exists at this point even in the scientific community.

    I'm enjoying Greene's show!!  I also really like the stuff they show on the Science Channel about cosmology.

    "Jesus died for somebody's sins but not mine." -- Patti Smith

    by followyourbliss on Tue Nov 08, 2011 at 08:31:32 AM PST

  •  core/cusp problem (22+ / 0-)

    of dark matter shows that, even without a central bulge the dark matter is spread evenly throughout small galaxies.  This indicates that dark matter may actually be a quantum effect.

    this quantum effect of "dark matter" is also indicated by the slowing down of Pioneer 10, called the "pioneer anomaly"

    the fundamental flaw in our understanding of gravity is the root cause of these misunderstandings.

    Gravity is not a force.  It is an effect.  

    there is no force-carrier for gravity.

    The effect of gravity is analogous to the Casimir Effect.

    while the Casimir Effect is a force created by exclusion of potential waveforms of electromagnetic energy, gravity is the effect of two mass objects drawing from the same potential field in a region of space.  The potential field that is the quantum distribution of potentiality of matter is known as "vacuum energy".

    please take the time to donate $5.00 to Wikipedia for the most comprehensive body of knowledge, publically generated, on the internet today.

    •  Yes, there is much more to the story of... (12+ / 0-)

      dark matter and energy. The matter does appear to be spread over large volumes instead of concentrated in the center of a galaxy. For my purposes of this diary, I felt it was important to keep things simple. Your links will be helpful for the readers who want to know more in depth information.

      Thank you for commenting.

    •  The Pioneer anomaly is mostly (8+ / 0-)

      considered solved..


    •  see my comment above (4+ / 0-)
      Recommended by:
      jim in IA, Larsstephens, KenBee, New Minas

      entitled 'take this with a big grain of salt'.

      You are talking about what the author I mentioned was writing about.

      The book is The Unobservable Universe

      It was interesting.  He sees great potential in the Casimir effect.

      I didn't say 'take it with a grain of salt' to dismiss the idea, but just to say the skeptic in me would love to hear the argument against his thought experiment, too.

      ...the train's got its brakes on and the whistle is screaming.

      by themank on Tue Nov 08, 2011 at 11:40:25 AM PST

      [ Parent ]

    •  Wasn't there a related effect with Galileo (2+ / 0-)
      Recommended by:
      p gorden lippy, New Minas

      when it made its several gravity assist passes by Earth?

      Heh. I always wondered if there was a Casimir angle to the observations. I never saw it stated so clearly that gravity is analogous but I'm nodding my head here. It makes a lot of sense that gravity is an interference effect caused by the (what?) gauge field state exclusions caused by mass being present?

      •  we know that a gravity well is formed (0+ / 0-)

        around a mass object.

        we know that time slows down in a gravity well and space contracts.

        We also know that only mass particles experience time, the quantum mechanic equation of non-mass particles does not have a time-based component.  

        it was this basic understanding that first led us to know that neutrinos have mass since they decay into other forms.

        the idea that mass creates a gravity well is well theorized, what is not theorized is the mechanism that creates this well.

        I postulate that dark energy is made from virtual particles, and that the virtual particles partially made by mass objects. (mass-particles create a substantial part of the quantum field).  This is a fancy way of saying that the quantum field of potential existence (whereby all particles have a potential ability to "pop" into existence anywhere in the universe) is really just the potential wave form of all matter in the universe which dissassociates into a potential field on a time scale of 10^-32s and re-integrates into location.  


        when matter re-integrates into our own time-space continuum it draws itself together from the potential field (the dark energy).


        when separate bodies of matter are drawing from the same quantum field (yes dorthy, the field is neutral and all matter in the universe shares the same waveform/potential field) then the exclusion of potential waveforms between the two bodies creates a pressure that is analogous to the casimir effect.

        •  The mass equivalent of the potential flux energy (0+ / 0-)

          would be sufficient to explain a lot of macro dark matter effects... except that dark matter has discrete location and this has been proven.

          I played around with this one about 15 years ago and tought it had legs... until there was solid evidence that galaxy-sized (and far more massive) clumps of dark matter were loitering about, slightly offset from the visible clumps of matter.

          Still.. I'm rooting for this description of yours being a piece of the eventual puzzle.

          •  one thing to consider (0+ / 0-)

            we know that potential waveforms of light have a measurable effect, even though their discrete existence is, by nature of the potentiality waveform, no where.

            it is likely that there is a multiplier effect as all potential locations of a particle's waveform exists in all locations at once, so a single particle has an effect everywhere at once.

            interesting too, Feynman suggested that only a single electron existed as its time based component works going both forward and back in time.

    •  no it doesn't and no it isn't (0+ / 0-)

      Gravity is a force.

      Dark matter exists.

      The fact that it's evenly spread indicates that it doesn't collide and slow down.

      Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

      by eigenlambda on Tue Nov 08, 2011 at 01:30:06 PM PST

      [ Parent ]

    •  Dark matter isn't evenly spread (3+ / 0-)
      Recommended by:
      eigenlambda, pico, J M F

      It clumps, just not quite as much as normal matter. (Why? Normal matter can emit light - photons! This costs them energy - and so they slow down.)

      For instance, we think that in the early universe dark matter was the first to form regions of high and low density (for complicated regions, normal matter couldn't), and then normal matter 'fell' into the 'gravity wells' of dark matter.

      We can also directly examine dark matter through gravitational lensing - from Einstein's equations, concentrations of mass cause various optical phenomenon (e.g. blurring, magnification, duplication, etc.) and examination of this tells us where matter is clumped. So we can definitely see dark matter's concentrations, and it definitely is not evenly spread.)

      However, dark energy is evenly spread (as far as we know), and it is believed to be a type of vacuum energy.

      As for the rest though... let's just say that your statements do not quite agree with the scientific consensus. I don't want to enter into a long essay here.

      •  OK - if dark matter clumps (1+ / 0-)
        Recommended by:
        J M F

        at that scale, what does that say about its quantum size?  In a universe of neutron matter (or denser), the ability and tendency to clump would argue that dark matter (whatever it is) is markedly sub-nuclear in size/scale, or is offset from the rest of the visible universe in some way.

        Quark sized or smaller?

        I am not religious, and did NOT say I enjoyed sects.

        by trumpeter on Tue Nov 08, 2011 at 03:02:38 PM PST

        [ Parent ]

        •  good question (1+ / 0-)
          Recommended by:
          J M F

          In principle, one could have an object which is intermediate between a neutron star and a black hole.   Many believe that the core of a neutron star is quark matter.   It is possible that dark matter could form a gravitationally bound object that was very dense.   But I have no idea how it would form, since the dark matter is moving relatively fast and only interacts gravitationally---it can't lose energy (like stars) and thus has trouble clumping on small scales.  On scales like galaxy size, maybe, but not smaller.

          •  Well, yes (2+ / 0-)
            Recommended by:
            eigenlambda, J M F

            Anything can form dense gravitationally bound objects. E.g. black holes. It's an interesting intellectual exercise as to what that would behave like (of course, depends on what dark matter is very much.)

            But in practice, no way for it to form. When dark matter was dense (in early universe), it was going way way way too fast to clump. The main way it loses energy is through expansion of the universe

            (If you've had quantum mechanics), recall that particles have a wavelength associated with them (de Broglie wavelength) based off of their momentum. Qualitatively, if you double the size of the universe, the wavelength doubles, and so the particles decrease in velocity. But of course, once dark matter has slowed down very much, it's way too thinly spread to clump.

        •  wait, what? (3+ / 0-)
          Recommended by:
          science, eigenlambda, J M F

          The average density of the universe is something like 5 hydrogen atoms per cubic meter. By 'clumping' I mean that dark matter forms regions of higher and lower density. By 'higher' I mean something like (making this up out of the top of my head) a million hydrogen atoms per cubic meter. Which is still very very little.

          For comparison, normal uncompressed  water has density of 1000 kg per cubic meter, or roughly 6* 10^29 hydrogen atoms per cubic meter.

          In addition, how do you define sizes? Nucleus implies the strong (color) force binding protons and neutrons together. If that's what you mean, since dark matter isn't protons/neutrons/etc. and it doesn't couple with the strong force, yes dark matter is smaller than the nucleus... just like electrons or neutrinos or whatnot are smaller than the nucleus.

          But as far as we are aware quarks, electrons, and all of these are point particles (preons - particles making up quarks - have been hypothesized for a while; my research adviser at CERN was a strong proponent of them. But absolutely no evidence whatsoever for them.) As for dark matter, we expect it to be a point particle as well. But I don't see why this has anything to do with the properties of dark matter.

          •  If you're looking at the early universe, (0+ / 0-)

            matter density would be MUCH earlier.  And I'm talking about before photons could travel freely.  In that instance (the first few hours, perhaps?) matter density would have been incredibly high - too high for there have been enough freedom for matter to have much opportunity for changes in density, but something had to have influenced the variable density of what followed.

            When the density of the Universe is as high as it appears to have been in the first few hours after the Big Bang, there really isn't much, if any, room for variation of nuclear particles or atoms - it's all just packed tight as sugar cubes in a box..  and when the box expands... what influences how the sugar cubes disperse?

            Does that make any sense?  I can visualize it, but don't have the math to explain it well.

            I am not religious, and did NOT say I enjoyed sects.

            by trumpeter on Tue Nov 08, 2011 at 04:09:40 PM PST

            [ Parent ]

          •  quark mass (0+ / 0-)

            isn't it interesting how much mass of a proton is actually relativistic (binding)?

            the component quarks, if measured individually, make up about .009% of the mass of the proton.

    •  Yes! Thank you (1+ / 0-)
      Recommended by:
      New Minas

      for pointing that out.

      Granted, I'm no physicist. But Einstein was quite clear about gravity being an EFFECT of curved spacetime. That quantum physicists have long treated gravity as a force--thereby causing them to search for a "carrier" particle (the graviton) that's never been found--has always irked me.

      I have long thought that the quantum physicists have taken a wrong theoretical turn somewhere. But I'm just some old hippie who reads too much; what do I know?

      Maybe the discovery of dark energy will straighten things out.

      Meanwhile...where the heck is that Higgs boson?

      There are two types of Republicans: millionaires and suckers.

      by Phil T Duck on Tue Nov 08, 2011 at 04:23:53 PM PST

      [ Parent ]

  •  I once read a post by a fundamentalist who (7+ / 0-)

    tried to refute the Big Bang by insisting "there had to be a spark to set off the gas."

    He / she didn't even understand the Big Bang was not an explosion, and therefore can't be explained as a flammable gas exploding in the presence of oxygen.

    Lea: "You're not going to fly into an asteroid field, are you?" Han Solo: "They'd be crazy to follow us, wouldn't they?"

    by Kimball Cross on Tue Nov 08, 2011 at 09:06:51 AM PST

    •  His intuition isn't far off... (1+ / 0-)
      Recommended by:
      p gorden lippy any reasonable definition, the Big Bang certainly was an explosion, and a "spark" is a decent metaphor for the as of yet unknown trigger.

      But how a metaphor repudiates anything is beyond me.

      A quant and damned proud of it.

      by Cera on Tue Nov 08, 2011 at 01:28:19 PM PST

      [ Parent ]

  •  I don't understand how you can put Dark Matter (7+ / 0-)

    and Dark Energy in a pie chart. Dark Matter and atoms are both "matter," and therefore their gravitation effects can be compared.

    Dark Energy, by definition, is not matter. Therefore, I don't see how you can compare it to Dark Matter and atoms.

    Lea: "You're not going to fly into an asteroid field, are you?" Han Solo: "They'd be crazy to follow us, wouldn't they?"

    by Kimball Cross on Tue Nov 08, 2011 at 09:08:45 AM PST

  •  Fascinating stuff, Jim. (5+ / 0-)

    Thank you for putting it in a way non-physicists can understand! The one-minute video is a hum-dinger, too, and I see there's much more available at the New Scientist.

    It brings to me the main thing I remember about physics, "mass is energy in motion." If we have mostly dark energy and dark matter ("mass"), is there a point at which the energy becomes more matter? Isn't CERN a huge atom smasher? Can those atoms be used to determine the nature of the dark matter?

    I know that's a lot of questions from a layperson, but if you have time, could you clear up my muddy understanding a bit?

    Thanks for the fine post!

    Meteor Blades: "Don't tell me what you believe. Tell me what you do and I'll tell you what you believe."

    by cotterperson on Tue Nov 08, 2011 at 09:12:42 AM PST

    •  I will get back to you later via a message... (3+ / 0-)

      if that is ok. You deserve better answers than I can give here.

      Thank you for asking those questions...

    •  Matter is bound-up energy (5+ / 0-)

      fixed into a stable (more or less) configuration. Some forms of it (self-obliterating virtual particle-antiparticle pairs) last barely measurable periods of time.

      Others, say, protons, might not decay before the universe ends.

      It has been proven in the lab to be possible to create matter from sufficiently high energy densities but it's probably easier to collect stray atoms from the interstellar vaccuum than to make matter from scratch in this fashion.

      What dark matter represents is the possibility that there are completely different ways to convert energy into stable and semistable configurations that interact differently (or not at all) with the forces (and effects) that influence what we have come to (rather parochially) define as normal matter and energy.

      For example, perhaps dark matter is composed of 'fixed' space-time metric - nothing more than flecks of especially dense space that are nearly frictionless to each other as well as to normal matter - but do have gravitational footprints... and as such can generate gravitational lens effects (even though they are themselves transparent to EM radiation).

      Now, what about with each other? Are there hierarchies of interaction among dark matter flecks? There do not have to be under a wide range of circumstances. But so far the best models to explain dwarf galaxy dark matter distributions suggest a very weak level of self-interactive compared to how regular matter interacts with itself. Ad if the level of self-interaction is nonzero, that means it could be a scalable effect. And if it's scalable, there may be extreme conditions in which... very, very interesting things happen... more dark matter forming...or something even more interesting.

      After all, what happens if these imaginary dark matter flecks decay? There is an expanding release of space-time metric  - just a little relaxation that expands out the cosmos a weeee bit.

      Only thing is, this happens over and over again, n-tillions of times a day, all over the cosmos.

      So, there you go - a fictional example of what dark matter/energy could be and a quaint imaginary model of how the two might fit together and in a vague way interact from time to time with so-called normal matter.

    •  Yes (4+ / 0-)

      Actually, the current leading hypothesis for what dark matter is, is that it's a new class of particle that we call 'supersymmetric'. (SUSY for short.) Note that this is purely a theoretical concept as of right now, but there are quite a few theoretical reasons for believing this. As well as a few experimental reasons NOT to believe this, so take with a grain of salt.

      One of the things CERN is looking for (in addition to the Higgs boson) is supersymmetric particles. I'm not a particle physics expert (though I did spend a summer at CERN), but I believe that CERN should have a high enough energy to determine (to a reasonable significance) whether supersymmetry really exists. If it doesn't, we're back to the drawing board.

  •  Two things, gravity does not suck, it acts through (6+ / 0-)

    the universe through multiple dimensions. The second thing is a lot of dark matter seems to be in supermassive black holes at the center of all known galaxies, a fact only recently discovered. Gravity, despite Newton and Einstein is still a mystery, and is the main stumbling block to all the current 'theories of everything'.

    May you live in interesting times--Chinese curse

    by oldcrow on Tue Nov 08, 2011 at 09:15:17 AM PST

    •  As noted below by themank, paradigm shift... (3+ / 0-)

      is perhaps in the future about our knowledge of gravity.


      •  A completely off the wall, nearly ignorant (0+ / 0-)

        opinion of mine is that gravity, which pushes masses together, and dark energy, which is pushing the universe apart, are the same thing, or at least different aspects of the same thing.

        May you live in interesting times--Chinese curse

        by oldcrow on Tue Nov 08, 2011 at 01:41:18 PM PST

        [ Parent ]

        •  Short answer: (8+ / 0-)

          Dark energy is perfectly described using Einstein's gravitational equations. The only reason it 'pushes the universe apart' is that it behaves differently from ordinary matter.

          To try and explain why, I'll give you an example of something else that behaves different from ordinary matter: Photons (light)

          If you put a bunch of matter in a universe, and then double the size of the universe, the amount of matter stays the same. Simple, right?

          However, if you take a bunch of photons in a universe, and double the size of the universe, the photons lose half of their energy! Why?

          Because when you double the size of the universe, you also double the size (wavelength) of the photons. And if you've had some basic physics, you'll recall that the energy of photons is based off of their wavelength - E=h/lambda. So, photons behave differently from matter (and this, by the way, is why photons make up so little of the energy density today - something like 10^-4 to 10^-5.) Photons basically slow down the expansion of the universe more than matter.

          On the other hand, if you have dark energy in a universe, and double the size of the universe, you have twice as much dark energy! So dark energy behaves differently from stuff that we understand - and this is why it causes the universe to be pushed apart, as you put it (to see exactly why, I have to go through the general relativity equations, but I don't think you want that :)

    •  no, the black holes are not dark matter (3+ / 0-)
      Recommended by:
      p gorden lippy, J M F, deben

      adding more mass to the center of a galaxy doesn't fix the non-Keplerian speed vs distance from the center curve.

      Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

      by eigenlambda on Tue Nov 08, 2011 at 02:00:56 PM PST

      [ Parent ]

  •  Empty space (4+ / 0-)

    To top it off, I've read an estimate that the ratio of matter to empty space is 1 to 500 trillion, by volume.

    That is a tremendously large amount of...  'something'?

    I think we are on the verge of an really interesting paradigm shift in our understanding of the nature of things. It's an exciting time.

    ...the train's got its brakes on and the whistle is screaming.

    by themank on Tue Nov 08, 2011 at 09:17:02 AM PST

  •  Ok that's 4 things now (5+ / 0-)

    that i would like found or explained.

    Where is the Higgs Boson - c'mon LHC!
    What is Dark matter - really?
    What does dark energy come from...
    Who found the first graviton...

    Every time history repeats itself, the price goes up...East Wing Rules

    by Pithy Cherub on Tue Nov 08, 2011 at 09:44:36 AM PST

  •  Could dark energy and/or matter have somehow (4+ / 0-)

    Existed prior to the Big Bang or do scientists believe it too was the result?

    I couldn't help wondering if dark energy/matter did somehow exist, if it somehow "sucked" our visible universe into existence from another, "parallel" universe.

    This ain't no party. This ain't no disco. This ain't no foolin' around!

    by Snud on Tue Nov 08, 2011 at 09:58:16 AM PST

  •  jim, so totally cool beans. (4+ / 0-)

    I love physics, but feel like others here: I get the feel, the art, and concept of it rather easily; the nitty gritty mathy part, not so much.

    You have made this tour, and the comment thread very enlightening and so much fun.

    Thanks. And if you ever get around to answering any of those question, how about putting them where we can all see?  Hint, hint.

    Science is hell bent on consensus. Dr. Michael Crichton said “Let’s be clear: The work of science has nothing to do with consensus... which is the business of politics. Science, on the contrary, requires only one investigator who happens to be right,”

    by Regina in a Sears Kit House on Tue Nov 08, 2011 at 11:06:27 AM PST

  •  i have a question (6+ / 0-)

    and that is about recognition for Vera Rubin. If I´m not misinformed then the two guys who discovered the microwave background, got the physics Nobel prize. And recently, the supernova study discovering the acceleration got that prize as well, for Perlmutter I believe. Both I find well justified. But the way you´ve described it here, Vera Rubin´s observations are completely on a par with those others, fundamentally changing our understanding of the universe. Wouldn´t she have deserved the same prize then? Did she get anything in comparable recognition?

    •  She is very deserving. More info in this... (5+ / 0-)

      link to an article...

      If you asked Rubin, she might tell you that her greatest contribution to science is her four children, all of who have scientific careers: two geologists, an astronomer, and a mathematician. But she's also been justly lauded for her research, having analyzed over 200 galaxies since 1978. She has won election to the National Academy of Sciences and snagged the 1993 National Medal of Science in the process. But the Nobel Prize continues to elude her.

      There have been so few women scientists honored by the Nobel Committee over the years: only two have won the physics prize, Marie Curie in 1903 and Maria Goeppert-Mayer in 1963. Marie Curie also won another in chemistry. Today is her birthday. Did you see the Google search screen graphic today?
  •  Dark Energy should be renamed to Invisible Turtles (4+ / 0-)
    Recommended by:
    marsanges, Snud, Wee Mama, Larsstephens

    I don't think anyone has a clue as to what it is. I believe it's just a fudge factor in equations that makes the observations fit our current understanding of physics.

    All of the fudge factors we have in all of our currently accepted physics represent a lack of understanding IMO.

    There is much we do not understand. Grade 3 indeed, I'd argue we are still in kindergarten.

    Regardless, thanks for a clear diary on a clearly baffling topic.

    Much appreciated.

    You could be listening to Netroots Radio. "We are but temporary visitors on this planet. The microbes own this place" <- Me

    by yuriwho on Tue Nov 08, 2011 at 11:45:24 AM PST

  •  Wonderful subject. (3+ / 0-)
    Recommended by:
    jim in IA, sargoth, Larsstephens

    I don't understand it that well, but I love it.  So let me ask a question.  Clearly, through all of the various images of known nebulae, there is a LOT of dust out there that we only see when it's sufficiently dense and being illuminated by stars or blasted by cosmic rays.  Could simply widely-dispersed dust account for the dark matter, or would that require far more dust than could be present?

    You can't spell CRAZY without R-AZ.

    by rb608 on Tue Nov 08, 2011 at 11:47:16 AM PST

    •  Apparently there is not enough. Using all... (2+ / 0-)
      Recommended by:
      Larsstephens, rb608

      means available to detect the matter and dust in visible light and beyond the visible, there is not enough normal matter to account for the effects of the dark matter we can't detect.

      Thanks for stopping by...

      •  I have to wonder about this. (2+ / 0-)
        Recommended by:
        Larsstephens, rb608

        We've just taken our first "baby steps" to be able to detect earth-sized planets orbiting local stars.  How can we measure much smaller distant matter such as dust and rocks?  There may be millions of "orphan planets" out there that are virtually invisible because they don't orbit a star.

        •  By how much light they block, (3+ / 0-)
          Recommended by:
          rb608, jim in IA, sargoth

          and by how they distort, and how much they distort, the light that does get to us from those distant sources.

          If there were enough dust to account for all of that mass, we would not be able to see as far as we can.  Also, the dust that is out there has some effect on spectrographs.

          I am not religious, and did NOT say I enjoyed sects.

          by trumpeter on Tue Nov 08, 2011 at 03:34:47 PM PST

          [ Parent ]

    •  No (4+ / 0-)

      Not at all.

      Note that dark matter is known to be about 27% of the universe, vs normal matter ~4%. So that's a 7-1 ratio.

      In addition, we can still see dust. How? Because when we have stars and etc. next to it - it heats up the dust, and the dust emits light! Even if it's in the middle of space, it's still emitting very low-frequency light (radio waves - which we can see with radio telescopes.)

      Dark matter, on the other hand, does not emit lit at all. Hence why it's 'dark' :)

  •  i'm guessing that dark matter and energy don't (1+ / 0-)
    Recommended by:

    exist. i hypothesize that the accelerating growth of the universe is an effect on the universe by the big bang like giant gravitational ripples in the universe carrying galaxies on their crests.

    Standing up for men and their interests does not constitute misogyny.

    by SetaSan on Tue Nov 08, 2011 at 12:07:34 PM PST

  •  Ethan Siegel: Starts with a Bang (1+ / 0-)
    Recommended by:

    This write is similar in style to one of my favorite bloggers, Ethan Siegel.  Starts with a Bang
    Here is his latest on Dark Matter

    For those who want to get the whole story I encourage you to read see the Greatest Story Ever Told.

  •  matter / antimatter collisions? (1+ / 0-)
    Recommended by:

    Maybe dark matter and dark energy is the legacy of all the matter/antimatter collisions that took place at the dawn of the universe?  That stuff had to go somewhere, right?

    •  Right... (2+ / 0-)
      Recommended by:
      science, Larsstephens

      From a NASA article...

      There are still a few dark matter possibilities that are viable. Baryonic matter could still make up the dark matter if it were all tied up in brown dwarfs or in small, dense chunks of heavy elements. These possibilities are known as massive compact halo objects, or "MACHOs". But the most common view is that dark matter is not baryonic at all, but that it is made up of other, more exotic particles like axions or WIMPS (Weakly Interacting Massive Particles).

      How could you go wrong with MACHOs and WIMPs?

      •  Huh, that article's very outdated (3+ / 0-)
        Recommended by:
        trumpeter, docmidwest, eigenlambda

        Basically, there are ways in which baryons (protons, neutrons, electrons and all that) behave differently from dark matter, and we can determine the amount of matter in the universe from that.

        We've calculated the amount of baryons in the universe to be 4.56 +/- 0.16 %. We've also calculated the amount of mass in the universe to be about 26-27%. There isn't any way to reconcile those two numbers (unless our cosmological model turns out to be completely wrong - unlikely given how good of a job it's doing of fitting the data.) The difference between the two is what we call dark matter - it's incredibly unlikely to be baryons.

        •  That's right (1+ / 0-)
          Recommended by:

          and one might mention that the observed baryons in the universe is somewhere around 2-3% (I don't recall the exact number), and we calculate 4.56 +/- 0.16% by measuring the amount of helium, deuterium, tritium and lithium -- their values depend sensitively on the number density of baryons.

          So there are still quite a few baryons out there that we don't see---possibly MACHOS or black holes or something else.  But it still is not more than 4.56% or so, and thus 90% or so of the dark matter can't be baryons.

    •  not the dark energy (1+ / 0-)
      Recommended by:

      If it exists, it has a fixed energy density as space expands, not at all like ordinary bits of energy.

      Michael Weissman UID 197542

      by docmidwest on Tue Nov 08, 2011 at 01:24:23 PM PST

      [ Parent ]

    •  It did go somewhere... (1+ / 0-)
      Recommended by:

      The "mass" of matter converts to pure energy when it meets anti-matter. Is there enough energy released to form "new" matter?  Or does entropy make this impossible?

    •  Where did the matter/antimatter energy go? (3+ / 0-)
      Recommended by:
      Larsstephens, eigenlambda, sargoth

      Answer from a cosmologist:

      The matter and antimatter annihilated, releasing photons. This is, essentially (more complicated but in principle) where the cosmic microwave background - photons left over the big bang -came from.

      So why aren't these photons superenergetic? Why isn't our universe mostly radiation?

      Well, it turns out that if you take a bunch of photons in a universe, and double the size of the universe, the photons lose half of their energy! Why?

      Because when you double the size of the universe, you also double the size (wavelength) of the photons. And if you've had some basic physics, you'll recall that the energy of photons is based off of their wavelength - E=h/lambda. So, photons behave differently from matter. And this, is why photons make up so little of the energy density today - something like 10^-4 to 10^-5. Photons basically slow down the expansion of the universe more than matter.

  •  Thank You - N/T (1+ / 0-)
    Recommended by:

    "Upward, not Northward" - Flatland, by EA Abbott

    by linkage on Tue Nov 08, 2011 at 12:53:59 PM PST

  •  Going away for awhile... Jim in IA (2+ / 0-)
    Recommended by:
    science, Larsstephens

    I need to vote and see my U.S. Representative. Continue to talk amongst yourselves and have a good time.

  •  thanks for clearing that up me. . seriously. . (0+ / 0-)

    If debt can be monetized for 30 years, why not wind for 30 days ?

    by stargapknight1 on Tue Nov 08, 2011 at 01:20:56 PM PST

  •  thanks for another content-free diary (0+ / 0-)

    and for egging on misconceptions in the comments

    Global warming is the inconvenient truth, nuclear power is the inconvenient alternative.

    by eigenlambda on Tue Nov 08, 2011 at 01:32:45 PM PST

  •  Jim-- (3+ / 0-)
    Recommended by:
    Larsstephens, jim in IA, KenBee

    I was away from the computer all day and didn't contribute, but I didn't need to.  Your diary was excellent, and your responses were pretty much spot on.    Thank you.

    FYI, a "Higgs Boson Announcement v3.0" diary will be posted Thursday afternoon.   It is just an update....nothing exciting to announce, except that there is a huge amount of LHC data being analyzed and the results (which will be definitive regarding the Standard Model Higgs) will be announced no later than the first week of March (and possibly as early as mid-December).

    •  I will watch for the Higgs diary. (2+ / 0-)
      Recommended by:
      science, KenBee

      And, I appreciate your comments about the diary. I knew I was stepping into some interesting territory. My depth of knowledge is limited on many details. I am always glad to have other Kos readers step in and answer questions and clear up wrong ideas. Thank you for your help.

  •  My understanding, (and it's limited) (1+ / 0-)
    Recommended by:

    is that the cosmic expansion, the Big Bang, was a non-Einsteinian event.  By that, I mean that the universe had to expand faster than the speed of light.  Otherwise it would not have been able to expand and would be a black hole.  Theories about WHY there was ever this initial cosmic expansion which otherwise defies physics as Einstein explained it, are incomplete.  

    One theory, arising out of string theory, is that the cosmic expansion that created our universe began as the collision, outside our realm of time and space (BEFORE the Big Bang) by a collision of M-branes.  (An M-brane is one of the more complex models of a string in string theory, one with lots of extra dimensions.)  The very idea that there was even such a thing as "BEFORE" the Big Bang runs counter to what we previously believed possible.  However, this is just one theory of many.

    The implication of it, though, is that there are forces affecting our universe that are outside our universe, and that one of those forces created the initial expansion of the universe so that everything today is not just a black hole.  

    And before anybody jumps to the conclusion I'm trying to imply some religious in this, God saying "Let's collide two M-branes and let there be light," -- no, I'm not.

    So I find myself wondering, is Dark Energy then just another expression of whatever it is that caused the Big Bang, some expansive energy from outside our the black box that is our universe and not necessarily PART of our universe.  Like a little boy shaking up a fish bowl, and the fish going, "What was that?  I don't see anybody disturbing the water, do you?"

    •  Nope... (0+ / 0-)

      ...cosmic inflation is a theory defined in a space that is a solution to Einstein's equations.  Also, the notion that universe "expands faster than the speed of light" is an unfortunate misunderstanding due to certain conventions and conveniences in cosmology.  Bottom line, a third party observing two galaxies recede from each other at "faster than the speed of light" isn't a violation of special or general relativity, but a failure to recall that the math applies only when determining the recessional motion of an object from an observer's own frame of reference.

      A quant and damned proud of it.

      by Cera on Wed Nov 09, 2011 at 03:36:57 AM PST

      [ Parent ]

      •  I'm going to assume you know (0+ / 0-)

        more about this than me, because it's the safest assumption.  But that doesn't gibe with my undestanding, so I would appreciate it if you could clarify and give me some links.  I only took undergrad cosmology.

        Einstein said that he thought that his "cosmological constant" had been a grave blunder.  From wiki:


        Einstein included the cosmological constant as a term in his field equations for general relativity because he was dissatisfied that otherwise his equations did not allow, apparently, for a static universe: gravity would cause a universe which was initially at dynamic equilibrium to contract. To counteract this possibility, Einstein added the cosmological constant.[1] However, soon after Einstein developed his static theory, observations by Edwin Hubble indicated that the universe appears to be expanding; this was consistent with a cosmological solution to the original general-relativity equations that had been found by the mathematician Friedman. Einstein later referred to his failure to predict the expansion of the universe from theory, before it was proven by observation of the cosmological red shift, as the "biggest blunder" of his life.

        So we have Einstein basically adding the cosmological constant as a fudge factor to his own equations to keep the universe from collapsing on itself, based on the clear observation, to him, that it wasn't collapsing or already collapsed.  The cosmological constant became useful anyway, despite Einstein's misgivings, after the discovering of Hubble's red-shift because it could be used to describe, but not explain, cosmic expansion.  So to say that it "arises" from Einstein's equations isn't necessarily accurate.  It was Einstein's fudge factor.

        Next, as to expansion faster than the speed of light -- I probably misunderstand or mistated that.  In cosmology, I did ask that question though, rather directly, "Can space expand faster than the speed of light," and I was given a flat answer of Yes, perhaps an oversimplified yes.

        One reason for this -- go back to the initial cosmic spark moment, all the universe's mass in a space proportional to the size of a planck constant.  That should have been, all other things being equal (and of course, they weren't) a black hole.  It shouldn't (all other things being equal) have been able to expand because the gravitational force should have exceeded the speed of light.  For it to expand, the expansion of space had to be faster than the speed of light just to keep it going and overcome gravity.

        I'm not trying to educate you about this, but asking you to help me understand this better.

        •  Well... (1+ / 0-)
          Recommended by:

          1. Don't worry about the history of how the field equations or the cosmological constant came to be.  Working mathematicians and physicists are principally concerned about deriving laws from known principles--including principles that emerge contemporaneously or even after a law might emerge.  In this case, we might choose to derive EFE using the principle of least action (Einstein-Hilbert action in this particular application).  First thing you should note is that we can linearly insert the constant into the equation.  We can derived the modified EFE as a result.  Setting it to zero gives us the constant free EFE Einstein originally devised.  This is completely valid.

          2. Here's one of the best non-technical of the category error I hinted lay behind the notion of "superluminal expansion."  Essentially, someone is naively taking something they call "distance," dividing it by something they call "time," and ending up with something they call "speed."  It's a bit more subtle than taking the distance between Oakland and Lisbon, dividing it by the time it takes to boil a pot of water, and calling it the air velocity of unladen swallow, but largely the same idea.

          3a. There is no gravitational "force" per se in relativity.  What you have are geodesics, which in the flat space-time of our common intuition translates to a "straight line."  It's in such a flat geometry that we can derive the Newton's laws of motion at low velocities and special relativity as velocities approach the speed of light.  But gravity doesn't figure into special relativity at all, which is concerned only with inertial (non-accelerating frames), and gravity is completely replaced by space-time curvature in general relativity.  That is to say configurations of matter and energy curve space-time, and as such curve geodesics as to impart acceleration on an object observed moving along that path.

          3b. Black holes evaporate.  That's not to say that this is the mechanism that triggered exponential inflation from the early compact state of the universe.  But consider a similar process at work in the early universe, although instead of a black hole with a macroscopic surface area you have a dense region that is so that the average velocity of matter inside is traveling at high fractions of the speed of light.  And all of it in an area little greater than 10^-70 m^2.  

          A quant and damned proud of it.

          by Cera on Wed Nov 09, 2011 at 08:13:19 PM PST

          [ Parent ]

          •  Thank you very much for taking (0+ / 0-)

            the time to reply!

            Now, rewriting what I said previously, but trying to stay consistent with what you're saying.

            From the less-technical link:

            "So the distance between two objects can be increasing faster than light because of the expansion of the universe, but this does not mean, in fact, that their relative speed is faster than light."  

            From a third party POV, they are traveling faster than the speed of light, but according to relativity, they are at rest and space is curving.

            The thing that surprised me when I first heard about this in cosmology was the concept that space itself could be warped in such a way as to do this, which challenged my previous, less-sophisticated understanding of relativity.  In fact, according to the way I was taught cosmology, parts of that initial expansion were accelerated so quickly away from where we are now (or warped away, in this way of explaining things) that they don't even exist in the same space-time bubble with us, essentially aren't even part of our universe, island universes.

            I'm going to take it that what I said was wrong, and that cosmic expansion "faster than light" isn't inconsistent with Einstein, but rather something compatible with it, although not necessarily dictated by it.  

            If so, the cause of the cosmic expansion is still a mystery.  The colliding M-brane theory (which is not even close to universally accepted) attempts to proffer a possible explanation for it.  This too is rather mind-boggling to me, because it violates my previous understanding of the whole Big Bang theory by suggesting a time before "time."  In a PBS of Sci-channel documentary I saw once, Stephen Hawking said, asking what happened before the Big Bang may be like asking what is north of the north pole.  And yet here we are talking about events north of the north pole.

            On the subject of evaporating black holes, there's a nice non-technical book, Black Holes and Baby Universes by Stephen Hawking.  However, as he explained it, it only applied to very very small itsy-bitsy black holes left over from the Big Bang.

            •  Think of it this way... (0+ / 0-)

              ...imagine you're floating in space and you watch two rockets accelerate to c on opposite bearings.  Measure the rate of separation between them from your point of view and you'll calculate it to be 2*c.  But you wouldn't say anything is moving at twice the speed of light.  That's because you measured the change in separation over time--something entirely distinct from motion despite sharing the same units.

              Throw in curved spacetimes, and you can get separation rates many times that the speed of light.

              Black hole evaporation is a feature of any black hole--however, the time it takes for a black hole to evaporate is proportional to the cube of its mass.  Cosmologists and astrophysicists are interested largely in those black holes that are sufficiently massive to have survived to the present day, and especially those that are not so massive as to prevent us from observing their final moments.

              A quant and damned proud of it.

              by Cera on Thu Nov 10, 2011 at 12:32:21 PM PST

              [ Parent ]

  •  My curiosity (1+ / 0-)
    Recommended by:

    is about the big bang. This was supposed to be all matter in the universe, compressed to a point, and it exploded. So, why do we get visual data that is almost the same age as the universe, from across the universe?

    If the big bang occurred to an infinitely small point of matter, and it all expanded out over the last 14 billion years or so, how do we see light that has been traveling for that same time? Is it bouncing off the outer skin of the universe, and we are really seeing reflected light?

    Curiouser and curiouser....

    Rooting for the Dishonest Politician. The one that doesn't stay bought but actually represents the voters.

    by KatGirl on Tue Nov 08, 2011 at 02:21:11 PM PST

    •  The big bang did not come from (4+ / 0-)

      a point.  It occurred everywhere.   All the big bang theory says is that the distance between all points was much smaller in the past than now.   It is likely that the universe is infinite, so there is no center and no edge.     If the distance between all points in an infinite universe gets much smaller, then the universe is still infinite.

      At the actual t=0, though, one is multiplying zero by infinity.  But I know of few physicists that actually think the distance between all points was exactly zero (quantum gravity would intervene).   But we really don't know.

      Many confuse "the universe" with "the observable universe".  The latter is the 14 billion light year radius sphere surrounding us, and we obviously can't see beyond that.  But that doesn't mean it is "only 14 billion light years in radius"---as I said, it might be infinite.

      •  A few minor quibbles (4+ / 0-)

        Observable universe is actually more like 46 billion light years in radius. This is because you have to take the expanding universe into account (essentially, there's just an integral - not hard at all - that you have to do.)

        In addition, one widely accepted theory in cosmology is something called inflation (not what happens with money), and there are many good reasons (and experimental reasons) to believe that it's correct. This is rather complicated to talk about the details (subject of graduate-level rather than undergrad-level class), so I'll just focus on the qualitative parts, but what inflation says is that in the first second of the universe, it expanded by a factor of at least e^60. In short, if inflation is correct, the universe must be at least 10^26 times the size of the visible universe.

        There is also something called 'external inflation', which is theoretical and can't really be proven (but has quite good theoretical reasons) which says that inflation expands faster than it could end in parts of the universe - basically, there will always be parts of the universe expanding at this insanely rapid speed. If this is true, the universe is effectively infinite in size.

        •  Eek, typo alert (1+ / 0-)
          Recommended by:

          In my response ahead, read 'ETERNAL' inflation, not 'external'.

          Sorry about that!

        •  I agree (3+ / 0-)

          (BTW, I've written papers with Guth and Linde, but haven't done much cosmology in recent years).

          Yes, it is 46 billion light years, but that tends to confuse people who don't understand comoving coordinates.  So I oversimplified.  

          If inflation is right (and I think that is likely), then you are right that the universe is at least 10^26 times bigger.   Infinity, of course, is bigger than that  :-)

          Wish there was a way to test eternal inflation....

          •  ooh, nice :) (1+ / 0-)
            Recommended by:

            I'm an undergrad who's only done cosmology in recent years (two papers out so far.)

            If you haven't seen them, Guth had a couple of eternal inflation papers out that I read and found really interesting; I particularly liked the 'Youngness paradox' as an illustration for the difficulties of judging consequences of eternal inflation (explanation for the Fermi paradox!.... or not.)

            My own work has been on inhomogeneities in the CMB (testing non-Gaussianity) thus far, which is pretty interesting too (or so I like to think.)

  •  Is dark matter REAL? More real than 'the ether'? (0+ / 0-)

    Is it smaller than atoms?
    Is it dark?
    Or is it a field? Like spacetime?

    It sounds bogus.

    •  Of course it is real (2+ / 0-)
      Recommended by:
      trumpeter, eigenlambda

      we measure its gravitational effects in many, many independent and different ways.   In answer to your questions:

      1.  It is believed to be an elementary particle, which is effectively pointlike, i.e. much, much smaller than atoms.

      2.  It is dark because it doesn't interact with photons.  That is the definition of "dark".

      3.  Spacetime is not a field, so I don't know what you mean.  Technically, all elementary particles are fields, but just very localized....

      •  Is there an actual theory of dark matter? (0+ / 0-)

        If not then isn't it just an unknown 'x'? Like the ether.

        I was thinking of the TV visualization of gravity fields in four dimensions, which I do think is realistic.

        If dark means it doesn't interact with light, what does that mean? Even gravity can bend light.

        Google says there is no theory of quantum gravity but your idea sounds like some kind of quantum phenomenon.

        Michael Green on TV said they had a nano experiment where two parallel plates which got  drawn together showing that empty space wasn't empty(?!)

        I want to get fired up but it sounds like a whole bunch of nothin.

        •  There certainly is a theory of (2+ / 0-)
          Recommended by:
          jim in IA, Snud

          dark matter.   Many extensions of the standard model of particle physics contain particles which match the properties of dark matter.     Earlier this morning, I looked at a model with extra Higgs doublets (don't ask...), and calculated how much dark matter they would provide and what the effects would be in underground dark matter detectors.  It is an extremely precise and mature science....and most believe that we will know what the dark matter is by the end of the decade.

          Yes, dark matter can gravitationally affect light, but it doesn't emit or absorb light.  That is what I meant.

          Dark matter has nothing whatsoever to do with quantum gravity.  It uses classical general relativity.

          Michael Green is correct---empty space is not empty--particle/antiparticle pairs are coming into and out of existence in vacuum all the time.  This is predicted (and was predicted long before the experiments) and it is now measured--and the measurements agree with the prediction.  It has nothing to do with dark matter.

  •  Ha! Love it. The universe is an unimaginably (1+ / 0-)
    Recommended by:
    jim in IA

    ...strange place, in the very best possible sense.  Thanks.

  •  If you haven't seen the Science channel's Curiosit (2+ / 0-)
    Recommended by:
    palantir, jim in IA

    y, do yourself a favor and watch it.

    The first episode was Stephen Hawking talking about how everything in the universe can be explained without the necessity for a "creator." Great stuff.

    It does me no injury for my neighbor to say there are 20 gods or no god. It neither picks my pocket nor breaks my leg. -- Thomas Jefferson

    by AtlantaJan on Tue Nov 08, 2011 at 06:31:19 PM PST

  •  Sorry to be so late to the party (0+ / 0-)

    Wonderful diary jim! Something I took a whack at.

    Oh, and thank you for the plug.

  •  A contemplation, (1+ / 0-)
    Recommended by:

    or meditation I feel very drawn to is, when I lie down in bed at night, I envision or feel myself drawn into the mattress by the force of gravity, and see myself on the underside of the world, stuck to it by the force of gravity.  I lift my arm and feel it flop down, drawn by the force of gravity.  To me, gravity, the weakest of the fundamental forces, is also the greatest.  It is a profound mystery.  

  •  thanks Jim! (2+ / 0-)
    Recommended by:
    jim in IA, Snud

    I could do this every day.

    Another thing that I find amazing?  The distances involved in the space photos such as the 'portion of Carina Nebula' you used.  The distance from one side of that photo to the other are likely tremendously larger than I can possibly comprehend.  Yet I look at it and say to myself, hmm, it looks like a large plume of smoke, maybe a few hundred feet high.  How can such huge features look so... familiar?

    And I'm pleased with a bit of politics today, too.  

    ...the train's got its brakes on and the whistle is screaming.

    by themank on Tue Nov 08, 2011 at 11:53:55 PM PST

  •  Reality as "hologram"? (1+ / 0-)
    Recommended by:
    jim in IA

    The end of the first episode of that PBS show, "Fabric of the Cosmos", discusses the idea that what we see as reality might be a "projection" of information from the edge of a black hole. Whoa. They didn't go into it too much but made it seem as if it's a well considered theory being explored by serious physicists.

  •  at the local scale (0+ / 0-)

    does dark energy have any significant impact?

  •  Pie chart: where's regular energy? (1+ / 0-)
    Recommended by:
    jim in IA

    The pie chart shows 72% dark energy, 23% dark matter, and 4.6% atoms. Where's the regular energy? Is that the other 0.4%?

    Then there's this:

    About 72% of the Universe is in a form of mass and energy capable of creating that acceleration. It is not known what it is.

    So dark energy may include some matter?

    Thanks very much for addressing this fascinating subject. We humans desperately need regular reminders of how ignorant we are.

    "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

    by HeyMikey on Wed Nov 09, 2011 at 08:04:55 AM PST

    •  Regular energy is part of the 4.6%. (1+ / 0-)
      Recommended by:

      Energy and matter are often expressed as having an equivalence by scientists. Einstein expressed in with E=mc². But, this dark energy stuff is not a form we are familiar with. We don't know the true makeup of it. More to come in the future studies.

      •  Why dark matter, dark energy expressed separately? (0+ / 0-)
        Energy and matter are often expressed as having an equivalence by scientists. Einstein expressed it with E=mc².

        OK, I get that. Then why are dark energy and dark matter expressed as separate entities? Is suppose there must be some distinguishing factor with no analog when describing regular matter and regular energy?

        Again, thanks for explaining all this to us curious lay people.

        "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

        by HeyMikey on Wed Nov 09, 2011 at 09:25:41 AM PST

        [ Parent ]

        •  Others more knowledgable than I have... (1+ / 0-)
          Recommended by:

          said a few things in the comments above that might address your question. I suggest you work your way up looking for the user name 'science' in particular. Exchanges between 'science' and several others were very interesting. I, for one, learned a lot.

          Thanks for your questions...jim

Subscribe or Donate to support Daily Kos.

Click here for the mobile view of the site