The science of present is built in part on two pillars of modern physics, and no one fully understands either one! Many books and articles have been written about each, but both authors and readers complain that the topics are difficult to grasp without the use of complex mathematics that would scare away all but the most dedicated nerds. It's true that to fully appreciate the elegance of either pillar one must put in a considerable effort to learn the underlying basics. But I believe we can get across the fundamental concepts without using math at all, or at worst, third grade arithmetic. As long as we understand as a given two short sentences and tattoo them in our brains (These two statements should be added to the Ten Commandments):
1. The speed of light is constant regardless of the movement of the source or the observer: Nature will contort herself into ridiculous paradoxes to preserve this fact.
2. The percentage certainty of a particle's velocity (% V) added to the percentage certainty of the location (% L) is less than or equal to one hundred percent. Written as: %V + %L < or = 100
If you memorize those two statements, that by itself will leave you more educated in the basics of Special Relativity and Quantum physics than 95% plus of the world's population. But to place you in the top 2%, let's look at each and talk about just a few of the stunning consequences that flow from them.
1. The speed of light is constant regardless of the movement of the source or the observer: Nature will contort herself into ridiculous paradoxes to preserve this fact.
That sounds simple enough, right? When scientists were able to finally measure the speed of light they got around 186,000 miles per second. Pretty dang fast! We'll call that quantity "C".
But when they started playing around with measuring how fast light was coming off of a moving object, like the headlight on a train, they were flabbergasted. The speed of the light was always C. It didn't matter if you measured a light that was moving while you were still, or if you were moving as well. No matter what, the measured velocity was always C.
In the Relativistic Train Robbery, top frame, two cops wearing blue caps take a shot at the robber with the money bag. One cop is stationary beside the track and the other cop is on the train. The bullets from the two different guns are going two different velocities when they reach the robber, just as common sense would predict. But when the cops use flashlights, the velocity of the light hitting the robber is the same from both cops! Why? Because the speed of light is ALWAYS constant for any observer regardless of the movement of the source or the observer
But this creates a paradox; If two observers are both moving relative to one another, say one is on a train and the other standing beside the track, how could they both get the same velocity if they measured the speed of the same light beam? If the onboard observer measured how fast the light from a headlamp was speeding away from him, and he got C, then the guy on the side of the track should see the light from that lamp moving at C + however fast the train was going. But he doesn't! It is as if the light is traveling two different velocities at the same time!
Every observer always got C as the measured speed of light, no matter how they were moving or how the light source was moving, thus giving rise to the sentence: The speed of light is constant regardless of the movement of the source or the observer.
How to explain it? Well, velocity is just distance per unit time, like 100 mile per hour or 10 feet per year. If the distance covered per unit time is different for each observer, and if the velocity of C remained constant, then then either time or distance must change!
If the observer moving at one-half of C in a rocket ship sees the light from his nose lamp racing away at C, and a stationary observer sees the light from the lamp also moving at C, then the observer must be, unknown to himself, in a sort of slow motion state. Time must be slowing down for the moving observer just enough so that the light seems to 'flash out' from his perch in apparent fast motion. And time slows down just enough so that the light seems to leave him at C. Which means, the faster he goes, the more time slows down.
Ahh, but there's another problem, illustrated above. If the moving observer could measure the distance the light beam was covering in a second, he could see that his spaceship was covering half the same distance per second. But recall that Nature will contort herself into ridiculous paradoxes to preserve the illusion that the speed of light is always constant for every observer, regardless of the source. To maintain the illusion perfectly, space itself has to contract for the observer in his line of motion. He doesn't feel it in anyway, but if we could glance at him as he speeds past us, he and his ship would seem squished to us.
An even weirder problem crops up when considering simultaneity. If there is a flash bulb exactly halfway inside the crew cabin of the rocket right above the head of the pilot, and that flash bulb goes off, the pilot sees the light hit both ends of his cabin at the same time, because the speed of light has to travel the same velocity in both directions from his point of view. But an observer outside will see the light strike the back wall first, as if the flash bulb were stationary; because the speed of light is always constant for him as well. Illustrated below.
Since the speed of light has to be constant in both directions for the pilot, he sees the flash hit the front and back of his cabin at exactly the same time. But because the speed of light has to be the same in both directions for the observer, he sees the flash hit the back of the cabin first! <Cue Twilight Zone Music>
At the turn of the century a twenty-something year-old clerk was pondering these dilemmas, and he came up with a radical idea. He proposed a solution of Maxwell's Equation for electromagnetism that encompassed the special situations where the velocity was constant, as in the three paradoxes above. Thus it was named Special Relativity.
A decade later he solved the same equations for cases near gravitational fields or involving acceleration and called it General Relativity. General Relativity today is the basis for almost all of Cosmology and much of astronomy. It is used to understand the behavior and nature of everything from Black-holes to the Big Bang to neutron stars, and it is GR that introduced the mind-bending ideas about space warps and time as the fourth dimension. And while many folks like me can talk about General Relativity and look pretty smart, don't be intimidated because, as the old saying goes: "No One Really Understands General Relativity!"
2. The percentage certainty of a particle's velocity (% V) added to the percentage certainty of the location (% L) is less than or equal to one hundred percent. Written as: %V + %L < or = 100
If we know with 95% certainty the velocity, then we only where the damn thing is to a certainty of 5% or less. If we push this inequality to the maximum, the velocity is measured to a 100% certainty, then we know nothing about the location of the particle. A lot of people when confronted with this are tempted to conclude that there really is a location, we just can't know what it is if we measure the velocity to a certainty. But that would be incorrect. What this fundamental rule means is that when the velocity of a particle is known to absolute certainty ...it doesn't have a location at all!
A simple equation very much like the version I've written above became known as the Heisenberg Uncertainty Principle named after Werner Heisenberg who first formulated it in 1927. The name was chosen for the simple reason that the more an observers knows about the location of a particle, the more uncertain they can be of the velocity and vice-versa. Like the observation that the speed of light is constant, the conclusions that flow from the Uncertainty Principle and other facets of QM give rise to several seemingly unsolvable paradoxes. The most commonly heard is that quantum objects behave as both a wave and a particle. A particle is simple enough to imagine, it's just a point in space. A wave is simple enough to imagine, it's a stretched out undulation, such as a water wave or a soundwave.
But to say a quantum object like an electron is both a wave and a particle is like saying a bird can be an animal and a musical note! They are two different, mutually exclusive objects, and yet in the bizarro world of the very small, where objects have neither a solid position and velocity, they're the same.
The Uncertainty Principle was at first disheartening to physicists. It knocked the idea of an elegant Newtonian Universe unfolding with clockwork precision for a loop. Upon first hearing of Uncertainty, physicists figured if they could never know for sure the position and speed of a particle, they could never predict what it will do or how it will react with other particles. In fact, if a particle has no location in time or the location is highly uncertain, cause and effect themselves can become meaningless.
Einstein himself criticized Uncertainty saying "God does not play dice with the universe!" The latter along with several other famous statements by Einstein have often been used by theists of various flavors to 'prove' Einstein was a believer in God. It's worthwhile to note that while historians disagree on the details, Einstein was born Jewish and seemed to profess a sort of pantheistic view that is inconsistent with traditional western religion. It's even more worthwhile to note that while Einstein was a hell of a physicist, regardless if he was an atheist or a theist or something else, his religious opinion was no more or less valid than yours or mine or that of the Head Clown at Barnum and Bailey's Totally Awesome Big Clown Extravaganza.
But a number of physicists working together soon learned to describe the range of possibilities in the particle's position and speed as an average of a wave type function and were able make valid predictions for both a single particle and groups of them. This analytical treatment of particle possibilities was called Quantum Mechanics and the direct applications include everything from the atomic bomb to the chips and microcircuitry in home computers.
The weirdness of Quantum Mechanics even attracted the attention of the House Committee on Un-American Activities during the McCarthy witch-hunts when they tried, unsuccessfully, to use Quantum Mechanics as a sort of odd platform to attack the patriotism of physicist Edward Condon (among others) accusing him of being a revolutionary or a communist sympathizer (And, no I'm not making this up):
[From The Demon Haunted World] "Dr Condon, it says here that you have been at the forefront of a revolutionary movement in physics called ... QUAN-TOM ... Mechanics. It strikes this hearing that if you are at the forefront of one revolution, you could be at the forefront of another ... "
Condon, quick on his feet, replied that the accusation was untrue. He was not a revolutionary in physics. He raised his right hand: "I believe in Archimedes' Principle, formulated in the third century B.C. I believe in Kepler's laws of planetary motion, discovered in the seventeenth century. I believe in Newton's laws...."
(A few years ago I would have chuckled at that anecdote. Sad to say, these days that chuckle has been replaced with a nervous, paranoid giggle as I think about some similar committee run by Rick Santorum and Bill Frist grilling Stephen Hawking or Richard Dawkins. "DR Dawkins, it has come to this committee's attention that you subscribe to an antiquated Godless ideological dogma called EVA--LUSHUN ...")
Again, if Quantum Physics sounds murky and vague, don't despair. As the old saying goes "No One Understands Quantum Physics!"
Today two fields of physics, Quantum Mechanics and General Relativity, completely dominate our understanding of the universe. One explains the very large, the other covers the very small.
But they are warring camps, rarely talking to one another. Each has its own language and its own mathematics. Neither one can be used to explain the phenomena the other covers. And today the race is still on to unify the two under a single theory: The theory of Everything. Stephen Hawking united a small portion of Quantum Mechanics with General Relativity when he deduced Hawking Radiation; a phenomena thought to occur near the event horizon of Black-holes. And there is much hope for String Theory or Loop Quantum Gravity. But for now, the Theory of Everything, if there is one, belongs to the Ghost of Science Future.
For those who are just starting to explore the weird, whacky world of relativity and quantum mechanics, I recommend Quantum Reality (Two opposable primate digits way up!) or Einstien's Universe: The Layperson's Guide or Einstien for Dummies.