# Relativistic Mass

Discussion in 'Physics & Math' started by Little Bang, Jul 1, 2015.

1. ### Little BangRegistered Member

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Does the gravity of relativistic mass affect the observer?

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3. ### AlexGLike nailing Jello to a treeValued Senior Member

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Relativistic mass (a highly misleading term) does not affect gravity.

5. ### Little BangRegistered Member

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So a particle moving past me at a velocity great enough to give it a relativistic mass equal to the Earth would go unnoticed?

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7. ### OnlyMeValued Senior Member

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Relativistic mass is an old term for the momentum of a mass with relativistic velocity.

The only mass that affects gravitation is rest mass.

The idea of relativistic mass is similar to thinking that a bullet or car gets "heavier" or more massive when it is moving. Its mass remains constant, but its momentum is proportional to the product of its mass and velocity.

It would be best to forget the phrase relativistic mass and just think momentum.

8. ### Little BangRegistered Member

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You did not answer my question, is the particle(with Earthlike momentum) undetectable?

Last edited: Jul 1, 2015
9. ### RajeshTrivediValued Senior Member

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Not strictly, rather first two lines, are incorrect.

10. ### AlexGLike nailing Jello to a treeValued Senior Member

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Yes, there would be no gravitational effect.

11. ### RajeshTrivediValued Senior Member

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The answer is No ! The relativistic mass will have gravitational impact.

a particle having a relativistic mass (gamma * M0) of the order of the Earth Mass will certainly have gravitational impact. Gravity is Einstein's baby GR. Sans mathematics I can say that stress energy tensor of the Einstein equations will take care of relativistic mass and will impact the curvature of spacetime.

In GR, you would note that the test particle (closer to a massive object) is either a photon or a particle with comparably very low mass, if the mass of the test particle is high (either of the two masses, rest or relativistic) then GR maths become absurdly difficult, so exact solution in such case may call for Numerical / Analytical approach.

12. ### AlexGLike nailing Jello to a treeValued Senior Member

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You really want to pay no attention to Rajesh. He seems to inhabit a universe of his own devising. In fact, you'd be well advised to put him on ignore.

13. ### Little BangRegistered Member

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This thread came from curious thought. If we have galaxies outside our ability to see and moving away from us at very near c would this explain the accelerated expansion we see?

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14. ### Little BangRegistered Member

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So E = m times 10meters/sec is meaningless as far as a gain mass?

15. ### RajeshTrivediValued Senior Member

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Thats boom !! You need to read a little bit of GR, my friend. Newtonian what you say is fine (gamma is almost 1, so both are same magnitude wise), but as soon as you talk of comparable relativistic mass as per OP, GR tensors come into play.

PS: There is nothing misleading about relativistic mass, it is gamma times rest mass, and all the experimental guys on cyclotron will vouch for this....you may like to read about radius/dia of a charged particle in cyclotron and how it deviates due to relativistic mass.

16. ### AlexGLike nailing Jello to a treeValued Senior Member

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Gravitationally, yes. M is rest mass and is invariant.

17. ### Little BangRegistered Member

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You disagree then, the particle is undetectable?

18. ### AlexGLike nailing Jello to a treeValued Senior Member

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Gravitationally there would be no effect from 'relativistic mass. The only gravitational effect would be do to the object's rest mass.

19. ### OnlyMeValued Senior Member

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Gravitationally, yes it would be undetectable. The particle's gravitational field while moving would be no greater than were it inertial relative to the earth.

20. ### OnlyMeValued Senior Member

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Prove it!

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21. ### OnlyMeValued Senior Member

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Rajesh, this is the Physics & Math section of the forum. Prove your position with math and/or provide a credible reference, in support.

Or perhaps you should be restricted to posting in the Fringe!

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22. ### OnlyMeValued Senior Member

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Little Bang,

Lev Okun's, The Concept of Mass (http://www.itep.ru/theor/persons/lab180/okun/em_3.pdf) covers the issue.

As Alex points out it would be best to ignore Rajesh on this issue.., until and unless he provides a credible argument... Even then take what he says with several grains of salt.

23. ### wellwisherBannedBanned

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If relativistic mass impacted gravity, it would increase pressure, such that space travel close to C would cause material compression. The pressure on the space ship would get higher and higher like adding more and more mass. Relativistic mass is not about pressure.