The Truth of Relativistic Mass

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Offline Pmb

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The Truth of Relativistic Mass
« on: 12/12/2013 03:11:37 »
I've come to learn that there's a great deal of misinformation floating around the Internet regarding what some people call relativistic mass in modern relativity and relativistic cosmology. The misinformation is that it's an outdated concept that nobody uses anymore. This thread gives solid proof that this claim is invlaid and that relativistic mass is alive and well in the wonderful world of Einstein's world of relativity.

If anyone wants to verify what I said as being true the all you need to do is follow the URLs given below so that they can see it for themselves. I have many recently published SR and GR texts on my book shelf which use the concept and so their claim is just plain wrong.
Let's start off with a perfect example. Alan Guth, a particle physicist/cosmologist at MIT. He's a perfect example of somone who uses relativistic mass (which he simply refers to as "mass"). He uses it in his lecture notes for his Early Universe course that he teaches at MIT. I placed a sample page online so that you can see it for yourself. It's at
There is a large percentage of modern relativity and relativistic cosmology textbooks out there right now which proves such a claim is bogus. There are simply no facts out in the physics world that is consistent with the claim that its outdated other than the mere claim that it's outdated. Particle physicist often make this mistake so if one tells you that the only mass that's used in relativity is rest mass, don't believe them because it's a false statement. Particle physicists simply aren't relativists. They're merely people who use relativity as a tool in their work. They don't study relativity as a field in itself. Such physicists rarely, if ever, use the concept of mass outside the area of application of particle physics. They simply don't know the limitations of the way they chose to define "mass." And the fact that those limits don’t occur in their work makes it irrelevant for them.

Counter examples are given in my article on the subject. I wrote an entire paper giving all the reasons why what I'm stating is true. There's just far too much to place in as single thread or post. The paper is called On the concept of relativistic mass and is located at for those with the skill set to understand it. For those who don't please just ask. A perfect counter example to the claim that nobody uses relativistic mass in "particle physics/accelerator physics" is given in a web page under CERN's website at

Notice that this page is to teach so please read what CERN wants you to learn.
The claim that it hasn't been used for over 20 years is demonstratably false as anybody who wants to look in a book can learn for themselves. I've provided a list to such textbooks and a link to where you can read it online if it's available. Here's how this problem got re-started back in the late 80's with an article by Lev Okun. And yes. I did say re-started because contrary to  popular belief Lev Okun didn't originate this spiel about mass. Lev Okun made an attempt to ban the concept from all of physics but failed miserably. A lot of amateurs and non-relativists claim that its not used tool. Relativistic mass widely used in relativity and cosmology textbooks
There were two notable articles to counter Okun's tirade. They are

In defense of relativistic mass by T.R. Sandin, Am. J. Phys., 59(11), Nov. (1991)
b]Putting to Rest Mass Misconceptions[/b] by Wolfgang Rindler, Physics Today, May (1990)

The USENET Physics FAQ had it wrong for a while until I explained these facts to Don Koks, the physicist who maintains those FAQs.

The following are books that use relativistic mass

Concepts of Mass in Contemporary Physics and Philosophy by Max Jammer,
Princeton University Press, (1999). 
Download Available:

A first course in general relativity by Bernard F. Schutz, Cambridge University Press, (2009), from page 88
Download Available:
Thus, n is a scalar. In the same way that 'rest mass' is a scalar, even though energy and 'inertial mass' are frame dependant … 

This demonstrates a clear example of the use of relativistic mass as another term for inertial mass. It also shows an example of the fact that some people mean relativistic masswhen they use the term mass unqualified.

Gravity from the ground up by Bernard F. Schutz, Cambridge University
, (2003). See page 241 
Download Available: 
Immediately we see a problem: "mass" has no unique meaning in relativity. 

Relativity: Special, General and Cosmological, Rindler,Oxford Univ., Press,
Download Available at:   
Introducing Einstein's Relativity, Ray D'Inverno, Oxford Univ. Press,
Download Available:
General Relativity: An Introduction for Physicists by M.P. Hobson, G. Efstathiou and A.N. Lasenby, Cambridge University Press, (2006) 
Download Available:

Relativity; An Introduction to Special and General Relativity by Hans Stephani, Cambridge University Press, (2004).
Download Available:
Cosmological Physics by John A. Peacock, Cambridge University Press, (1999).
Download Available:
Basic Relativity by Richard A. Mould, Springer, (1994). 
Einstein's General Theory of Relativity: With Modern Applications in Cosmology by Grøn, Øyvind (2013)
Download Available:

« Last Edit: 12/12/2013 03:56:25 by Pmb »


Offline David Cooper

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Re: The Truth of Relativistic Mass
« Reply #1 on: 12/12/2013 20:53:28 »
I've been wondering about this for a while, but I've only now got round to looking up the formula needed to calculate the relavistic mass of a moving object, and it seems to tie in very neatly with the time dilation and length contraction. At 86.6% the speed of light, for example, the length of the moving object in the direction of its movement is halved and so is the amount of time that passes for it. If I'm using the right formula for relativistic mass, the mass will also have doubled at this speed. So, what I'm now wondering is whether this actually matches up with the amount of energy that has to be put into the object to get it up to that speed.


Offline yor_on

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Re: The Truth of Relativistic Mass
« Reply #2 on: 12/12/2013 22:03:33 »
Pete, are you happy with the statement that the Higgs field (Higgs bosons) is what makes mass. To my mind it is related to the concept of inertia, not mass. Or do you find mass explained by it?

Just sat listening to the Nobel prize takers referring to it as 'mass'. And I can't agree. Let us assume that it is mass, further let us assume that it then must interact as 'restmass'. Restmass is what you measure, being at rest with what you measure on, here I will define that as being in a shared uniform motion. So we now have a definite distinctive tell tale of what a uniform motion is, don't we? It's when you gain this mass interacting with a Higgs field. But wait, what about me accelerating, to then go back to a uniform motion? Does the restmass change? Nope. But doesn't this field need a motion to interact? Why would it treat a uniform motion close to light the same way, relative somethings restmass, as 'no motion' at all, as defined relative infalling light?

And how should one visualize this field under relativistic circumstances, your distances shrinking due to contraction etc?

And then we have the 'mass' created by a particles energy. And that one becomes a circular argument to me. As a particle has a energy it must have a mass, as mass can be transformed into energy etc etc. None of those defines what restmass is? Or better expressed, how it come to be, as it seems to me?

Nota bene, Einstein has the better definition of mass to me. Not the Higgs. Another problem becomes if it is accelerations that creates a 'inertial mass'. if it is so then restmass is not defined, but inertia seems to be. That will then split the definition of inertia from restmass. In that case the equivalence principle seems to come into question as it uses a constant uniform acceleration as equivalent to for example Earths gravitational field?

And you can't use it to define a relativistic mass either as it seems to me? Because me moving uniformly, close to lights speed in a vacuum, must have a higher relativistic mass than when being comparatively 'still', as defined by incoming light blue-shifting in the direction of my uniform motion (using so called 'fixed stars' for this argument). And it must blue shift.
« Last Edit: 12/12/2013 23:09:02 by yor_on »
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