Do objects gain mass while approaching light speed?

[LightningInAJar]

I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true? What keeps things of mass from reaching the speed of light or beyond? I assume matter doesn't accumulate higgs-bosons while in motion?

 

[Ibix]

Yes it is true. "Relativistic mass" is now a deprecated concept, as it is simply a confusing synonym for total energy. Mass, with no qualifier, means the invariant mass.

The reason massive objects cannot reach $c$ is that they are always free to regard themselves as "at rest", by the principle of relativity. Thus they always need to increase speed by $3×10^8\mathrm{m/s}$ to reach lightspeed.

Higgs bosons don't work by accumulating on things anyway.

 

[Orodruin]

Please read this: https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/

 

[Dale]

I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true?

They do not gain invariant mass, which is the thing that most physicists mean when they use the word mass.

What keeps things of mass from reaching the speed of light or beyond?

No finite amount of energy or momentum is sufficient to reach the speed of light.

 

[Ibix]

What keeps things of mass from reaching the speed of light or beyond?

I'm going to expand a bit on my previous answer here. There are many ways to approach this.

I like my answer because it follows immediately from Einstein's postulates.

Dale's answer also works. Kinetic energy is $E=(\gamma-1) mc^2$ and momentum is $p=\gamma mv$ where $\gamma=1/\sqrt{1-v^2/c^2}$, so no matter how much energy or momentum you supply you can only approach lightspeed because $\gamma\rightarrow\infty$ as $v\rightarrow c$. (Incidentally, if you define relativistic mass $m_r=\gamma m$ then $p=\gamma mv$ becomes $p=m_rv$, so the "relativistic mass goes to infinity" argument is just this one, but in obsolete terminology.)

Or you can observe that the mass is the modulus of the energy-momentum four vector, and things moving at light speed have a zero modulus. So "massless" and "can only travel at the speed of light" are synonyms in relativity, and "massive" and "cannot travel at the speed of light" are synonyms.

I'm sure there are other arguments. It depends what you like.

 

[Dale]

Or you can observe that the mass is the modulus of the energy-momentum four vector, and things moving at light speed have a zero modulus. So "massless" and "can only travel at the speed of light" are synonyms in relativity, and "massive" and "cannot travel at the speed of light" are synonyms.

This one is my actual preference, but usually it doesn't help beginners.

 

[vanhees71]

I'd only be pedantic and not call it modulus. It's $p_{\mu} p^{\mu}=m^2 c^2$ with $(p^{\mu})=(E/c,\vec{p})$. So $m^2 c^2=(E/c)^2-\vec{p}^2$. The fundamental form of Minkowski space is not positive definite (and it's crucial to be so!) and thus it doesn't induce a norm on Minkowski space.

For particles and for reasons of causality you must have $m^2 c^2=p_{\mu} p^{\mu} \geq 0$ though, and that's why $m^2 \geq 0$. One should also note that the case of massless "particles" is a special case, and one should not take the particle picture to seriously.

 

[Orodruin]

For particles and for reasons of causality you must have $m^2 c^2=p_{\mu} p^{\mu} \geq 0$ though, and that's why $m^2 \geq 0$.

Someone should tell the tritium decay experiments … 😁

 

[Ibix]

I'd only be pedantic and not call it modulus.

Is there a better name?

 

[vanhees71]

That's a good question! I'm not aware of a common name for a Minkowski product of a vector with itself.

 

[Mister T]

What keeps things of mass from reaching the speed of light or beyond?

The geometry of spacetime. Either there is an absolute fastest speed or there isn't. We know from doing experiments and designing equipment that there is.

 

[LightningInAJar]

If hypothetically we had a spaceship traveling faster and faster in space, but it's fuel tank isn't located on board and therefore not part of the ship's total mass could it then reach lightspeed? If say there were Dr. Strange portals transferring fuel from Earth to the moving ship over potentially unlimited distance. Could the ship be propelled much faster if the fuel mass becomes irrelevant?

Also did we learn anything new from the recent experiment that extracted matter from photons?

 

[Ibix]

If hypothetically we had a spaceship traveling faster and faster in space, but it's fuel tank isn't located on board and therefore not part of the ship's total mass could it then reach lightspeed?

No. As already stated, nothing with non-zero mass can reach light speed. Full stop.

If say there were Dr. Strange portals transferring fuel from Earth to the moving ship over potentially unlimited distance.

If you are using magic you are only limited by what the scriptwriter wants. Magic does not work in the real world.

Also did we learn anything new from the recent experiment that extracted matter from photons?

Which experiment do you mean?

 

[PeterDonis]

If hypothetically we had a spaceship traveling faster and faster in space, but it's fuel tank isn't located on board and therefore not part of the ship's total mass could it then reach lightspeed? If say there were Dr. Strange portals transferring fuel from Earth to the moving ship over potentially unlimited distance. Could the ship be propelled much faster if the fuel mass becomes irrelevant?

This is getting very, very close to the sort of unfounded speculation that is off limits here at PF.

The short answer to all of your questions is: no. What makes it no is the fact that the geometry of spacetime has a particular causal structure. (That is basically what @Mister T in post #11 was getting at.)

Also did we learn anything new from the recent experiment that extracted matter from photons?

No. The physics involved has been understood for decades; it just wasn't experimentally feasible to actually do it until now.

 

[malawi_glenn]

If hypothetically

https://www.physicsforums.com/insights/how-to-avoid-breaking-physics-with-your-what-if-question/