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

[workmad3]

Hang on there. Relativistic mass does not contribute toward space-time curvature.

I said it wasn't necesarilly correct, just something that helped me resolve the issues in my mind initially :)

 

[Idjot]

Who says it "answers everything"? It seems that your real objection is that physicists are happy to dispense with the notion of an absolute frame as long as there is no evidence for one (and they are not dogmatic about the fact that there never could be, although there are some good arguments for judging it to be very unlikely). You on the other hand seem to have some preexisting philosophical bias for thinking there must be one regardless of whether there is any evidence to support such a notion.

If time dilation has been documented many times, then why wouldn't time dilation be considered evidence of the existence of an absolute frame? It seems to me that if velocity were purely relative that a paradox would truly exist, rather than what we've already documented as time dilation.

 

[JesseM]

I can appreciate ideology by this definition. But a skewed perspective, like in the twins paradox does not indicate a paradox. It is merely an illusion that would be accounted for anyway, so there would never be a paradox to begin with.

But physicists who talk about the twin paradox point out that it is not a genuine paradox, so what are you objecting to? Just the name? If they called it the twin-apparent-paradox-as-seen-by-students-who-don't-yet-fully-understand-SR would you be happier?

This is probably a subject for it's own thread, but do you really believe that the limits of time are dictated by electromagnetic radiation?

I don't, I think they're dictated by the Lorentz-symmetry of all fundamental laws of physics, the laws of electromagnetism just being one example of a set of Lorentz-symmetric laws.

Why not "idealize" a formula for time dilation at "idealistic" speeds above c?

Because unlike with slower-than-c clocks, there's no way to derive theoretically how faster-than-c clocks would behave based only on the assumption that the laws of physics are Lorentz-symmetric.

There are a number of absolute quantities in relativity such as proper time between two events on a worldline, which all frames will make the same prediction about. There is no absolute reference frame in SR, but why do you think we "should be" looking for one?

Why shouldn't we? If you accept big bang theory you might consider CBR to be a little more qualified than other frames for such a role.

A "preferred frame" is defined as one where the laws of physics work differently than other frames, not just one that looks special relative to the distribution of matter. In any case, even if you did believe in absolute time, how would you go about demonstrating that the CMBR frame is the absolute frame? Or would we just have to take it on faith?

Why should we? It's simple. If everything is moving, everything is experiencing time dilation.

"Everything is moving" isn't really a meaningful statement unless you can experimentally demonstrate an absolute rest frame. If all frames are on equal footing, then for any object you can find a frame where it is at rest, and other frames where it's moving.

The age and velocity of an object should be measured by it's own local rate of time elapse relative to the absolute frame. That is the only way to make realistic comparisons between the properties of celestial bodies. Otherwise the results will be "skewed" as in the paradox. I just feel like we should be striving to view the universe in this way right now, even if we should choose a surrogate absolute to get us started. Does this make any sense to you or do I just sound like a crackpot? Haha.

You're free to pick a certain frame and do all your calculations from there, but that'll just be a sort of aesthetic preference on your part, you haven't given experimental evidence that this frame is more "correct" in some objective sense than any other.

Up and down are illusions caused by graviry. Time is real. Aging actually takes place. Differences in speed really cause differences in aging. Why not strive to find out what those differences really are rather than just what they are relative to each other?

We do find out what the differences really are, whenever two clocks are brought together to compare time elapsed at a single location. It's only when the clocks are spatially separated that there's no objective way to define which has aged more "at a single moment", because different frames define simultaneity differently so they have different opinions about what event on one clocks' worldline is simultaneous with an event on the other clock's worldline. For example, one frame might say the event of a clock reading 20 seconds is simultaneous with the event of another clock reading 16 seconds, while another frame might say the event of the first clock reading 20 seconds is simultaneous with the event of the second clock reading 25 seconds. If these clocks both read the same time when they passed next to each other earlier, then which is aging faster? Just as there is no objective truth about whether two objects at different locations are at the "same height" in space because there is no objectively correct way to orient an up/down axis to define height, so in SR there is no physical way to determine an objective truth about whether two events occur at the "same time", although you can objectively define the proper time between events on a single object's worldline.

Exactly. Just because we don't know which star is actually aging faster than the other does not mean that one isn't. Just because we can't tell which object is actually moving at a higher velocity than the other does not mean that one isn't. If we can accept c as an absolute, we can do the same for time somehow. We just have to find the right system. Maybe it'll end up being big bang related or maybe it'll end up being black hole related or even atom related. Whatever it is, we have to discover it eventually.

Why do you think we "have to"? It's logically conceivable that all the fundamental laws of physics we discover in the future will continue to be Lorentz-symmetric ones, and if this is the case there can never be a basis for saying one inertial frame is more correct than any other. You obviously have a strong philosophical preference for the idea that there is an objective truth about simultaneity, but there's no evidence in current physics for such an idea, and there's also nothing illogical or contradictory about the idea that there's no coordinate-independent truth about whether events occur at the "same time" just like I'm sure you believe there's no coordinate-independent truth about whether they occur at the "same height" or the "same distance along the x-axis".

 

[Division]

The faster you go, the more mass you gain (not fat gain, just so I'm understood on that). This doesn't mean that nothing can go faster than light, it's just that, nothing that we can handle or see can go faster than light.

However, there are theoretical particles that do go faster than light. An example of these particles are the Tachyon. The Tachyon is a particle originally teorized by Albert Einstein.

I'm not a physics expert, so you have to talk to someone that knows a little more about this than I do, I only tell you from I have read on the internet and in a few books.

 

[JesseM]

If time dilation has been documented many times, then why wouldn't time dilation be considered evidence of the existence of an absolute frame? It seems to me that if velocity were purely relative that a paradox would truly exist, rather than what we've already documented as time dilation.

What kind of paradox do you think would exist? In particle accelerator experiments, for example, you can see that a particle's decay time increases with its velocity, by just the amount predicted by the time dilation formula. Since the particles are traveling in a circular accelerator I suppose they don't really have inertial frames of their own, something similar is true for particles like muons that are created by cosmic rays hitting the upper atmosphere, where the particle's speed is such that it would decay before it reached the surface if it wasn't for time dilation. There's no paradox here either though, in the muon's inertial rest frame clocks at rest relative to the Earth would be running slower but because of the relativity of simultaneity, clock #1 at the position the particle was created would be out-of-sync with clock #2 at the position the particle decayed, so that (time on clock #2 when particle decayed) - (time on clock #1 when particle was created) would be predicted to be greater than the lifetime of the particle in the particle's rest frame in spite of the fact that each individual clock was running slow in this frame.

 

[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.