Two Spaceships, .90c - Why No Faster Than Light?

[DrGreg]

It really is a paradox

But physicists who talk about the twin paradox point out that it is not a genuine paradox, so what are you objecting to?

As an aside, to be pedantic, I have to point out the "twins paradox" really is a paradox, according to some meanings of the word. I googled for some definitions in online dictionaries and references and found...

a statement or situation that may be true but seems impossible or difficult to understand because it contains two opposite facts or characteristics

a statement or group of statements ... can be an apparent contradiction that actually expresses a non-dual truth

an apparent contradiction which is nonetheless true

a statement that is seemingly contradictory or opposed to common sense and yet is perhaps true​

 

[JesseM]

As an aside, to be pedantic, I have to point out the "twins paradox" really is a paradox, according to some meanings of the word. I googled for some definitions in online dictionaries and references and found...

True, I was thinking of "paradox" in the sense that the logic of SR could be used to come to two genuinely contradictory physical predictions (like each twin predicting the other one would be younger when they reunited), so there is no actual paradox in this sense. But "paradox" can also be used in a looser sense to refer to an apparent contradiction which is actually resolvable, or even just "something which flies in the face of common sense/expectations", so in that sense you could say the twin paradox really is a paradox of sorts.

 

[hitmeoff]

Its simple, Just take Einsteins basic equation E=mc$$^{2}$$. Here we see an energy-mass equivalence, meaning that energy comes from mass and vice versa mass comes from energy.

As a particle moves faster and faster its mass increases, as its mass increases the particle requires increasingly more energy to continue accelerating it. If a particle has any mass, it will take an infinite amount of energy to be able to accelerate it to the speed of light. So any particle with mass would never be able to be accelerated to the speed of light. Photons which are massless can move at the speed of light because they have a rest mass of zero. Now you may ask why a photon itself cannot go faster than c if it is massless. The reason is because a photon is a particle that is always moving and if a particle moves it has momentum. If a particle has momentum then it has mass, in the photon's case its mass is the energy a photon carries divided by c$$^{2}$$.

Say what?

A photon is always moving, and its always moving at the speed of light, there fore its has momentum and it has a moving mass. Because it is never not moving and does not exist in a non moving state, it has no rest mass. No rest mass means it can go as fast a c, but i has moving mass therefore it cannot go faster than light.

 

[DaveC426913]

Its simple, Just take Einsteins basic equation E=mc$$^{2}$$. Here we see an energy-mass equivalence, meaning that energy comes from mass and vice versa mass comes from energy.

As a particle moves faster and faster its mass increases, as its mass increases the particle requires increasingly more energy to continue accelerating it. If a particle has any mass, it will take an infinite amount of energy to be able to accelerate it to the speed of light. So any particle with mass would never be able to be accelerated to the speed of light. Photons which are massless can move at the speed of light because they have a rest mass of zero. Now you may ask why a photon itself cannot go faster than c if it is massless. The reason is because a photon is a particle that is always moving and if a particle moves it has momentum. If a particle has momentum then it has mass, in the photon's case its mass is the energy a photon carries divided by c$$^{2}$$.

Say what?

A photon is always moving, and its always moving at the speed of light, there fore its has momentum and it has a moving mass. Because it is never not moving and does not exist in a non moving state, it has no rest mass. No rest mass means it can go as fast a c, but i has moving mass therefore it cannot go faster than light.

While this is a succinct primer of relativistic speeds, I don't see why you've posted it here. It has no relevance has to the OP's question.