#### Comment Preferences

• ##### Not really(0+ / 0-)

Newton's second law in the form F = ma doesn't work relativistically.  Oddly, it works fine in the form that Newton preferred, which is that the net force on an object equals the rate of change of the object's momentum with time.  It's just that the relativistic expression for momentum is different from the expression used by Newton (see my post below)

There are different notions of mass.

In Newtonian physics mass is either what is measured on a balance in a gravitational field (gravitational mass), or the ratio of the net force on an object to the resulting acceleration (inertial mass).

In relativity the mass of a system is equivalent to the total energy of the system divided by the speed of light squared.  This turns out to have much deeper implications than I can explain in a short post.

In the Standard Model of Particle Physics mass of fundamental particles is a result of how strongly they couple to the Higgs Field.

All of these are different in sometimes small and other times big ways, but each exists within a particular theoretical framework.

IOW, many concepts in science, including mass, are defined within particular theories,  Change the theory, and you change the definition.  But once you change the theory, you can't always use the definition from that theory within one of the other theories.

"Trust only those who doubt" Lu Xun

[ Parent ]

• ##### You're saying "not really" to the creator of the (0+ / 0-)

theory of relativity; see the Einstein passage I quote in a previous comment.

• ##### From wikipedia(0+ / 0-)

It is not good to introduce the concept of the mass M = m/sqrt{1 - v^2/c^2} of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the ’rest mass’ m. Instead of introducing M it is better to mention the expression for the momentum and energy of a body in motion.

— Albert Einstein in letter to Lincoln Barnett, 19 June 1948 (quote from L. B. Okun (1989), p. 42[1])

Even Einstein could change his mind, and in this case he did.  You are also arguing from authority.  In the end no one person decides what works best in science.  In the physics community the idea of relativistic mass is considered as less objective than that of invariant mass.

"Trust only those who doubt" Lu Xun

[ Parent ]

• ##### thanks for the interesting comment.(0+ / 0-)

I'll give the matter further thought.

You are also arguing from authority.
As were you in saying "you wouldn't get a job at CERN".  The fact is that we all quote authorities every day -- we would get nowhere if we had to prove everything ab initio every time.
In the end no one person decides what works best in science.
This I can fully agree with.
In the physics community the idea of relativistic mass is considered as less objective than that of invariant mass.
That could well be; I have noticed that many physicists subscribe to the delusion that constructs such as mass, energy, quanta, orbitals etc. have an objective reality independent of the theory they are embedded in.  This was the case with time too, at one point.

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