Does time have a speed?

[Thorham]

It doesn't actually matter. Apparently photons don't experience the passing of time. However, why is a rest frame required in the first place? What would the problem be with measuring things from a photons perspective it it wasn't affected by time dilation?

 

Anyway, lets try something else. How about the speed of an object relative to space?

[swansont]

Aren't they at rest from their own perspective?

 

We have no physics that works for v=c, or in a proposed rest frame of a photon. There's no basis for claiming anything is one way or another.

[elfmotat]

It doesn't actually matter. Apparently photons don't experience the passing of time. However, why is a rest frame required in the first place? What would the problem be with measuring things from a photons perspective it it wasn't affected by time dilation?

 

Are you asking what physics would be like if it wasn't the way it is? We can't use physics to describe situations which violate physics.

 

 

Anyway, lets try something else. How about the speed of an object relative to space?

 

This is the same question you've been repeating. It's equivalent to asking what the absolute velocity of something is. There is no such thing - I thought I was pretty clear on that.

[Thorham]

We have no physics that works for v=c, or in a proposed rest frame of a photon. There's no basis for claiming anything is one way or another.

Okay, makes sense.

 

There is no such thing - I thought I was pretty clear on that.

You can keep saying that, but I don't see how motion always has to be relative. I sure hope it's not because relative motion is all we see, because that doesn't mean much.

[elfmotat]

You can keep saying that, but I don't see how motion always has to be relative. I sure hope it's not because relative motion is all we see, because that doesn't mean much.

 

I think it would help if you try to define exactly what you mean when you say "a velocity that isn't relative." What would that mean? Come back to me with a definition and I'll tell you why it fails.

[StringJunky]

You can keep saying that, but I don't see how motion always has to be relative. I sure hope it's not because relative motion is all we see, because that doesn't mean much.

Imagine you are sitting on a rock in the empty vacuum of space with absolutely nothing around you. You see a rock in the distance getting bigger with time. Are you moving towards the rock or is the rock moving towards you? Because you feel stationary – but you may actually be moving uniformly - it seems the rock is moving towards you. You will have the same experience if you sat on the other rock looking where you are now. This is why velocity is always relative to something because you have to choose what your reference point is.

Edited November 11, 2014 by StringJunky

[Strange]

Aren't they at rest from their own perspective?

 

No. Photons travel at the speed of light from every frame of reference. Which is why the photon's perspective is not a valid frame of reference; otherwise you would have to say that they travel at the speed of light relative to the speed of light. Which makes no sense.

 

 

How do you know this?

 

Because people have tried. Directly and indirectly. These are some of the most accurate experiments ever performed.

 

Isn't that caused by time dilation? Would massless particles experience time dilation? If not, then couldn't you simply say that the speed of a photon traveling in the same direction as another photon is zero from the perspective of both photons?

 

So now you want to invent so new (also undetectable) physics to try and make your erroneous idea work?

 

Except for the fact that these unseen things, if they're there, determine what we do see.

 

If they determine what we see then they should be detectable. If you can't detect them or their effects, then it is indistinguishable from not existing.

Anyway, lets try something else. How about the speed of an object relative to space?

 

Relative to nothing? How would you measure that?

[MigL]

What does the fact that Thorham hasn't got a clue about frames of reference have to do with the 'speed' of time ?

[ajb]

The key point is that in special relativity by observer, inertial frame, 'point of view' we mean the same thing. That is a choice of inertial reference frame; a way of setting up some coordinates. For all massive particles it is possible to find an inertial frames for which that particle is considered at rest. You may then further insist that this particle is at the origin of the coordinate system you set-up. Anyway, 'point of view' in special relativity then means 'as measured in a frame for which the object is at rest'.

 

You cannot do this for photons. There are no inertial frames for which the photon can be considered at rest. Thus what one could mean by 'the photon's point of view' is obscure. It cannot correspond to what one would usually mean in special relativity. Thus statements like 'photons not experiencing time' and so on need to be taken carefully. Usually these statements come from looking at the limit that the mass tends to zero, and this can give some insight. However, great care need to be taken and one must not take these statements too seriously.

[Thorham]

Imagine you are sitting on a rock in the empty vacuum of space with absolutely nothing around you. You see a rock in the distance getting bigger with time. Are you moving towards the rock or is the rock moving towards you? Because you feel stationary but you may actually be moving uniformly - it seems the rock is moving towards you. You will have the same experience if you sat on the other rock looking where you are now. This is why velocity is always relative to something because you have to choose what your reference point is.

While I understand that, what I want to know is why motion would always be relative just because we see motion as relative?

 

No. Photons travel at the speed of light from every frame of reference.

Yes, but isn't it impossible for us to observe anything while moving at the speed of light (we can't get there)? Seems to me that the speed of light while moving at the speed of light is unknown then.

 

So now you want to invent so new (also undetectable) physics to try and make your erroneous idea work?

No, I'm just asking.

 

If they determine what we see then they should be detectable.

First of all, who says that it isn't detectable? Just because it's not detectable now, means nothing. A thousand years ago we couldn't detect a whole range of phenomena, because we didn't have the means and lacked all the necessary theories.

 

Second, why would you assume that everything that exists can be detected by us?

 

If you can't detect them or their effects, then it is indistinguishable from not existing.

Or it's just unknown.

 

Relative to nothing? How would you measure that?

Space isn't nothing, otherwise it wouldn't be able to expand and curve.

 

The key point is that in special relativity by observer, inertial frame, 'point of view' we mean the same thing. That is a choice of inertial reference frame; a way of setting up some coordinates. For all massive particles it is possible to find an inertial frames for which that particle is considered at rest. You may then further insist that this particle is at the origin of the coordinate system you set-up. Anyway, 'point of view' in special relativity then means 'as measured in a frame for which the object is at rest'.

What about a hypothetical fixed point in space?

 

You cannot do this for photons. There are no inertial frames for which the photon can be considered at rest. Thus what one could mean by 'the photon's point of view' is obscure. It cannot correspond to what one would usually mean in special relativity. Thus statements like 'photons not experiencing time' and so on need to be taken carefully. Usually these statements come from looking at the limit that the mass tends to zero, and this can give some insight. However, great care need to be taken and one must not take these statements too seriously.

Got it.

[Strange]

While I understand that, what I want to know is why motion would always be relative just because we see motion as relative?

 

It is not just an observation. It is also based on the idea that the "laws of physics" are the same regardless of your state of motion:

http://en.wikipedia.org/wiki/Galilean_invariance

 

Yes, but isn't it impossible for us to observe anything while moving at the speed of light (we can't get there)? Seems to me that the speed of light while moving at the speed of light is unknown then.

 

Yes, the speed of light at the speed of light is not defined because moving at the speed of light is not a valid frame of reference.

 

Space isn't nothing, otherwise it wouldn't be able to expand and curve.

 

But there is nothing in space to measure your position or velocity against.

 

What about a hypothetical fixed point in space?

 

How would you define that? How do you know it is fixed?

 

Can you come up with a way, even in principle, to measure a fixed point or an absolute velocity?

 

[ajb]

What about a hypothetical fixed point in space?

This is mathematically what you do. You pick some point to the origin of your coordinate system. How do you pick this point or mark it? What you could do is place a massive particle there and along as that particle was not experiencing any acceleration you are okay.

Edited November 11, 2014 by ajb

[elfmotat]

While I understand that, what I want to know is why motion would always be relative just because we see motion as relative?

 

You aren't listening. Try to come up with your own definition of "absolute velocity." $20 says the way you'll do it is by referencing something you claim has a preferred frame. Except we know for sure (we've done a buttload of tests) that such a preferred frame does not exist.

 

Before relativity and after Maxwell, physicists thought that light propagated through a medium called "aether." The aether's rest frame was taken to be a preferred frame, i.e. absolute velocity would be measured relative to it. If you ever want to know how fast you're moving relative to the aether, all you need to do is measure the speed of light and compare it to what it would be if you were at rest. That's exactly what Michelson & Morley tried to do. So what went wrong? They figured out that no matter how they tried to do the experiment, it would always give a velocity of zero. In other words, it didn't matter how they oriented the experiment or moved it around, it seemed like we always remain stationary relative to the aether.

 

Special relativity was proposed as a solution to this puzzle. Einstein started with the principle, "there is no test an inertial observer can perform to determine whether or not he is moving or stationary." Another way to say this is, "the laws of physics are the same for all inertial observers." This was not a new idea (called the

principle of relativity), and was actually widely accepted up until Maxwell's equations, which implied that the speed of light should be independent of reference frame. That's when people tried to abandon it in favor of aether. Einstein said, "no, forget about aether, it doesn't exist. Let's keep the principle of relativity and Maxwell's equations and see what happens." And what happens is we get a theory that agrees wonderfully with experiment.

 

So, how do we know there are no preferred frames? We've done tests! You keep trying to drag this into the metaphysical, but it's really as simple as that. We're talking about physics after all - comparison with experiment is the end game.

 

 

First of all, who says that it isn't detectable? Just because it's not detectable now, means nothing. A thousand years ago we couldn't detect a whole range of phenomena, because we didn't have the means and lacked all the necessary theories.

 

It would be very easy to spot if a preferred frame existed. Particle accelerators, for example, should work differently depending on the time of the day or year due to Earth's rotation and motion around the Sun. But so far the laws of physics look identical for all inertial observers.

 

 

Second, why would you assume that everything that exists can be detected by us?

 

Why do you assume physicists would be interested in such things? If it can't be detected then it can't be corroborated, and so it belongs on the philosophy scrap pile. Can you prove that pink goblins don't inhabit the core of the Moon? Of course not, but to believe in such things when there is no evidence is ludicrous.

 

 

Space isn't nothing, otherwise it wouldn't be able to expand and curve.

 

However the coordinates you use to describe it are completely arbitrary. The universe doesn't care whether you call a particular point "A" or "B." It continues doing what it does regardless of your choice of coordinates.

 

 

What about a hypothetical fixed point in space?

 

Fixed in which reference frame?

[between3and26characterslon]

Obviously Thorham is struggling to understand some fundamental concepts and no-one has properly explained these, all that has come forward is the higher level results of these concepts which clearly aren't making sense to him so:

 

Gallileo was on a ship one day sailing in a constant breeze and therefore at a constant speed, the water he was sailing on was very flat. He was in the captains quarters and looked out of the porthole and saw the outside passing by, when he turned his gaze to a candle burning nearby he noticed the smoke from the candle rose straight up. He then took a small object and dropped it to the floor noticing it fell straight down and when he rolled a ball accross the floor it went in a straight line.

 

He surmised that travelling in a straight line at a constant speed was no different to being at rest and so the Principle of Relativity was born. In more modern language we are saying that a frame of reference that is moving in a straight line at a constant speed and one that is at rest are no different. These are called inertial frames.

 

More succinctly put, the laws of physics in one inertial frame are no less simple than in any other inertial frame. That means the laws of physics are the same and you don't have to take account of your movement - you are stationary

 

So you are in a plane flying in a straight line at a constant speed roughly East to West, the blinds are down and there is no turbulance. You are at rest in your frame of reference (the plane) and there is no experiment you can conduct within the plane to detect the speed you are traveling at. This is beacuse you and your apparatus are at rest in this frame. If you drop a ball it falls straight to the ground.

 

I am on a train travelling in a straight line at a constant speed roughly North to South, the blinds are down and the track is very smooth. I am at rest within my frame of reference (the train) and there is no experiment I can conduct within the train to detect the speed I am traveling at. This is beacuse I and my apparatus are at rest in this frame. If I drop a ball it falls straight to the ground.

 

From the outside we can measure your plane travelling at 500mph relative to the ground and my train travelling at 100mph relative to the ground but the speed of your plane relative to my train is in no way connected to the ground. If you were to magic the ground away you would be left with the speed of the plane relative to the train.

 

I think I am stationary and you are moving and you think you are stationary and I am moving whereas we are actually both moving relative to each other.

 

If there was a frame of reference that was not moving, i.e. absolutely at rest, then all other frames would be in absolute motion and when you drop something in your plane it would not fall straight to the ground, you would have to take into account your absolute motion.

 

Hopefully you will now understand that to say something is not moving has no meaning.

 

Something that is not moving in your frame of reference (i.e the ball on the plane, you put it on the table and it stays there) is moving in my frame of reference. All motion is relative, we can both be at rest in the same frame of reference or we can both be moving relative to each other (even though we think we are at rest and the other one is moving) but you cannot have the condition where one is absolutley at rest and the other is absolutely moving.

Edited November 11, 2014 by between3and26characterslon

[Thorham]

It is not just an observation. It is also based on the idea that the "laws of physics" are the same regardless of your state of motion:

http://en.wikipedia.org/wiki/Galilean_invariance

Yes, why wouldn't they remain the same, but what does that have to do with it? Everything appears to be relative because we don't have, don't know of, and can't make an absolute reference frame. It seems to me that the problem isn't with absolute motion, but with the inabilities of the observers.

 

But there is nothing in space to measure your position or velocity against.

Sadly that's not the only problem. Space itself isn't absolute. It can be curved, and it's expanding. You'd literally have to be outside of what we call space, and if this space is everywhere, and not something local, then you can forget it.

 

You aren't listening.

Wrong. I'm simply not blindly accepting what people tell me is the truth, especially not when people don't know the truth because all they have are models. Models don't dictate reality, reality dictates the models, and in reality the idea of absolute motion not existing seems absurd.

 

Try to come up with your own definition of "absolute velocity."

I can't.

 

Except we know for sure (we've done a buttload of tests) that such a preferred frame does not exist.

No, we don't know that for sure. We don't know what the universe is, so we can't reasonably make such claims.

 

Special relativity was proposed as a solution to this puzzle. Einstein started with the principle, "there is no test an inertial observer can perform to determine whether or not he is moving or stationary."

You can't know that, because we don't know if there are directly measurable mechanics behind motion. Something that causes motion to be possible. Or the mechanics that cause particles to have mass, etc. As long as we don't know these things, we can't reasonably make these claims.

 

You keep trying to drag this into the metaphysical, but it's really as simple as that. We're talking about physics after all - comparison with experiment is the end game.

That implies that you'll never look for anything more if your theories don't give you any reason to look for more. I'm not sure I like that, because you might have found things that none of the models predicted would exist. Things you're only going to find if you look for them.

 

The problem is that there may be a set of mechanics which create the laws of physics we're measuring and modeling. If these laws of physics can be described by themselves, without needing to know of these mechanics that are behind them, then you'll never look for them, because your now complete model doesn't give you any reason to. If those mechanics are measurable somehow, then you're missing things simply because you didn't think looking for anything more was necessary.

 

There is no end game.

 

It would be very easy to spot if a preferred frame existed. Particle accelerators, for example, should work differently depending on the time of the day or year due to Earth's rotation and motion around the Sun. But so far the laws of physics look identical for all inertial observers.

Oh really? How on earth does absolute motion cause the laws of physics to change? I say that all motion is ultimately absolute even if relative motion is all that ordinary observers can see, regardless of what any models tell you. These models are created after reality, and they only describe what we see.

 

Obviously Thorham is struggling to understand some fundamental concepts and no-one has properly explained these, all that has come forward is the higher level results of these concepts which clearly aren't making sense to him so:

I understand perfectly fine what you just explained. I just don't agree that all motion is relative just because we see all motion as relative.

[Strange]

Yes, why wouldn't they remain the same...

Because, if they were not the same, you could detect your abolute motion. If everything is identical, regardless of your state of motion, then any one state of motion is the same as any other.

 

 

I just don't agree that all motion is relative just because we see all motion as relative.

 

So it is a religious view. You don't care about the evidence, you are just going to believe it anyway.

[Thorham]

Because, if they were not the same, you could detect your abolute motion. If everything is identical, regardless of your state of motion, then any one state of motion is the same as any other.

Yes, but why does that matter? The physics remain the same, so you can't use differences in the laws of physics to detect absolute motion. Big deal.

 

So it is a religious view. You don't care about the evidence, you are just going to believe it anyway.

No, it's not a religious view. I simply don't agree with absolute motion not existing, and would certainly like to see this evidence.

[Strange]

Yes, but why does that matter? The physics remain the same, so you can't use differences in the laws of physics to detect absolute motion. Big deal.

 

No, it's not a religious view. I simply don't agree with absolute motion not existing, and would certainly like to see this evidence.

 

Well, it is up to you to provide some evidence for this undetectable thing. Until you do, there is no reason for anyone to consider it. You might as well say that invisible pink unicorns are what cause motion.

[Thorham]

Well, it is up to you to provide some evidence for this undetectable thing. Until you do, there is no reason for anyone to consider it.

I really couldn't care less.

[Strange]

I really couldn't care less.

 

I doubt anyone else does, either.

[elfmotat]

Wrong. I'm simply not blindly accepting what people tell me is the truth, especially not when people don't know the truth because all they have are models. Models don't dictate reality, reality dictates the models, and in reality the idea of absolute motion not existing seems absurd.

 

Hey, it looks like somebody is finally figuring out what physics is! It generally goes like this: step 1) guess model, step 2) compare model predictions to experiment. Physics cannot and does not give you anything more than a testable model, and nobody has ever claimed otherwise. It's your misconception if you think that science answers meaningless metaphysical questions. It's your problem if you can't wrap your brain around the idea of there being no absolute velocity.

 

 

I can't.

 

So then what the hell are you arguing about?! If you can't even define the thing you're so adamant must exist, then why in the world should I be wasting my time with this nonsense?

 

 

No, we don't know that for sure. We don't know what the universe is, so we can't reasonably make such claims.

 

I don't know how to argue with such a non-argument.

 

 

You can't know that, because we don't know if there are directly measurable mechanics behind motion. Something that causes motion to be possible. Or the mechanics that cause particles to have mass, etc. As long as we don't know these things, we can't reasonably make these claims.

 

Just stop with the metaphysical bunk already. This is a science forum. If you're not interested in science then you can move to the philosophy section.

 

 

That implies that you'll never look for anything more if your theories don't give you any reason to look for more. I'm not sure I like that, because you might have found things that none of the models predicted would exist. Things you're only going to find if you look for them.

 

The problem is that there may be a set of mechanics which create the laws of physics we're measuring and modeling. If these laws of physics can be described by themselves, without needing to know of these mechanics that are behind them, then you'll never look for them, because your now complete model doesn't give you any reason to. If those mechanics are measurable somehow, then you're missing things simply because you didn't think looking for anything more was necessary.

 

There is no end game.

 

Nobody cares if you disagree with the scientific method. That's the way science works. If you want to propose an alternative to the scientific method then go propose it in the philosophy section.

 

 

Oh really? How on earth does absolute motion cause the laws of physics to change?

 

Because that's what "absolute velocity" means, by any standard definition of the word! In the example with aether, Maxwell's equations were expected to be different depending on your speed through the aether. But no laws of physics are changed depending on your velocity, as discovered by experiment. If some preferred frame existed then we should be able to see it, because it means by definition that some laws are velocity-dependent.

 

 

I say that all motion is ultimately absolute even if relative motion is all that ordinary observers can see, regardless of what any models tell you. These models are created after reality, and they only describe what we see.

 

These are just meaningless metaphysical assertions.

 

 

I understand perfectly fine what you just explained. I just don't agree that all motion is relative just because we see all motion as relative.

 

Strange said it already, but this is basically the definition of a religious view. You have some preconceived notion of how the world should behave, and you ignore all evidence to the contrary. Since you've demonstrated a lack of willingness to argue in an intellectually honest manner, I don't think I'll be participating in these shenanigans any longer. Your attitude and style of debate are incredibly tiresome.

 

 

I really couldn't care less.

 

In regard to any further posts: ditto.

[MigL]

I told you not to get him mad.

Now you really went and did it.

[Thorham]

In regard to any further posts: ditto.

Well, at least it's over

[Phi for All]

Well, at least it's over

 

And you didn't have to learn anything.

[swansont]

Yes, but why does that matter? The physics remain the same, so you can't use differences in the laws of physics to detect absolute motion. Big deal.

 

 

One could say the same thing about unicorns. Is it reasonable to insist that unicorns exist, while admitting that there is no way to detect them? Is that science?