Does time have a speed?

[elfmotat]

Also, I thought I provided a fairly convincing argument that there can't be any "mechanisms," as you describe, which "account for motion." Place a ball on the ground, and then start driving. The ball, in your rest frame, has velocity/kinetic energy. In its own rest frame the ball has zero velocity/KE. How can any mechanism both cause something to move and not cause something to move, depending on what frame you analyze things from?

[Thorham]

Your question about chemistry just shows that when you start to strip it down, you eventually reach a point where the answer isn't chemistry, it's physics. When you strip physics down, you reach a point where you are asking questions that physics does not answer, but there's no other field down there that scientifically answers the questions.

Or you could say that chemistry is just a subset of physics, and that physics may very well end up answering these questions up to a certain point (the only problem is that you can keep asking).

 

You're simultaneously saying that you're not asking philosophical questions, while at the same time asking philosophical questions. It's quite maddening.

No, I'm not asking philosophical questions, I'm just asking what causes certain phenomena. How is 'What causes motion?' philosophical, and 'What causes birds to be able to fly?' not a philosophical question? They're exactly the same kind of questions.

 

Also, congrats! You're officially the first person I've ever met who doesn't believe in Newton's first law of motion.

Why would I not believe this to be true? Really, when did I say that things will stop moving after a while, even when no forces are acting on them?

 

Newton answered this for simple cases involving slow-moving objects: force causes [change in] movement.

Right. Now I'll get back to my motionless clock. Elfmotat asked 'Motionless according to what?', right? I answered 'Absolute motionlessness'. This was apparently a problem. But couldn't you say that something is motionless if no force ever acted upon it? Or if the effect of all forces that ever acted on something was countered by exactly the same amount of opposite force?

 

The notion of absolute velocity also seems to be a problem. But isn't an amount of force absolute?

 

You would think the notion of inertia was completely obvious.

Perhaps it's obvious. Some amount of force acted on a body, and the effect of this force is somehow not lost. How that works is of course another question.

 

Also, I thought I provided a fairly convincing argument that there can't be any "mechanisms," as you describe, which "account for motion." Place a ball on the ground, and then start driving. The ball, in your rest frame, has velocity/kinetic energy. In its own rest frame the ball has zero velocity/KE. How can any mechanism both cause something to move and not cause something to move, depending on what frame you analyze things from?

You just said that force causes movement. There's nothing relative about that. If an amount of force acted on something, then it moves, if no force ever acted on something, then it doesn't.

[swansont]

 

You just said that force causes movement. There's nothing relative about that. If an amount of force acted on something, then it moves, if no force ever acted on something, then it doesn't.

 

But you can't conclude that. The absence of an acceleration only tells you the velocity of something is constant. It does not tell you it is zero. Zero velocity is a chosen convention (or frame) but there is no physics that will tell you that it is the correct choice.

[elfmotat]

No, I'm not asking philosophical questions, I'm just asking what causes certain phenomena. How is 'What causes motion?' philosophical, and 'What causes birds to be able to fly?' not a philosophical question? They're exactly the same kind of questions.

 

You asked, "why are particles able to move?" From there, at the classical level, I can point you to Newton's laws. If you ask why Newton's laws are true, you're in the realm of metaphysics (philosophy).

 

Why would I not believe this to be true? Really, when did I say that things will stop moving after a while, even when no forces are acting on them?

 

Stop moving according to who? The problem here is that you're still thinking in terms of something either having velocity or no velocity. When you ask a question like, "what causes motion," and we point out that there's no need for any causes by citing Newton's first law, you refuse to accept it!

 

 

Right. Now I'll get back to my motionless clock. Elfmotat asked 'Motionless according to what?', right? I answered 'Absolute motionlessness'. This was apparently a problem. But couldn't you say that something is motionless if no force ever acted upon it? Or if the effect of all forces that ever acted on something was countered by exactly the same amount of opposite force?

 

No. Again, Newton's first law. If an object is moving at 12 m/s in some reference frame, and I know it's never been acted on by any forces, then I know that the speed of the object has always been 12 m/s in this reference frame. There is also an equally valid frame where the object has always been moving at 5 m/s, and 10⁸ m/s, etc.

 

 

The notion of absolute velocity also seems to be a problem. But isn't an amount of force absolute?

 

In Newtonian physics, yes, force is "absolute" in the sense that a force vector will be the same in all inertial frames.

 

 

You just said that force causes movement. There's nothing relative about that. If an amount of force acted on something, then it moves, if no force ever acted on something, then it doesn't.

 

YOU said that, not me! I never said anything of the sort. I don't appreciate when people put words in my mouth.

 

A force which, in one reference frame, will "cause movement," will also cause the object to stop moving in another frame. So the same force is both causing and stopping "movement," depending on which frame you decide to use when you analyze the problem.

[Strange]

Some amount of force acted on a body, and the effect of this force is somehow not lost. How that works is of course another question.

 

"How it works" is a philosophical question: why is the universe like it is. I guess you could develop a set of theories based in a universe where inertia didn't exist. It would end up being very, very different from this one. Why don't we live in that universe? Ask a philosopher.

 

And, again, what does this have to do with the fact that velocity is relative?

 

You just said that force causes movement. There's nothing relative about that. If an amount of force acted on something, then it moves, if no force ever acted on something, then it doesn't.

Acceleration is not relative. Consider the earlier example of being in space with nothing visible except another space craft. If the relative speed between you and the other craft is changing then you can determine whether it is you or her (or both) that is accelerating. But you still can't determine anyhting other than your relative velocity.

[Thorham]

You asked, "why are particles able to move?" From there, at the classical level, I can point you to Newton's laws. If you ask why Newton's laws are true, you're in the realm of metaphysics (philosophy).

I don't understand why asking 'what causes something' is such a problem. You can ask it about all kinds of things and get a concrete answer, but when you ask it about motion it becomes a problem. Doesn't make sense to me.

 

Stop moving according to who? The problem here is that you're still thinking in terms of something either having velocity or no velocity. When you ask a question like, "what causes motion," and we point out that there's no need for any causes by citing Newton's first law, you refuse to accept it!

Of course I don't accept it. It implies science knows everything there is to know about motion. Why would that be the case? How could you possibly know that? Because there's no need? According to what? Equations that describe some behavior that we see?

 

No. Again, Newton's first law. If an object is moving at 12 m/s in some reference frame, and I know it's never been acted on by any forces, then I know that the speed of the object has always been 12 m/s in this reference frame.

But why would it be moving if no force has ever acted on it? It just does out of nowhere?

 

YOU said that, not me!

Sorry, got the quotes mixed up:

 

Newton answered this for simple cases involving slow-moving objects: force causes [change in] movement.

A force which, in one reference frame, will "cause movement," will also cause the object to stop moving in another frame. So the same force is both causing and stopping "movement," depending on which frame you decide to use when you analyze the problem.

Yes, that's relative movement. But what about absolute movement? What's so strange about the concept of absolute movement? Motion causes an object to gain mass, right? I assume this mass increase doesn't get undone because something appears to be motionless. Which means that that which causes the mass increase is still there.

[Strange]

What's so strange about the concept of absolute movement?

 

What would cause that?

 

Motion causes an object to gain mass, right? I assume this mass increase doesn't get undone because something appears to be motionless.

 

It does. The so-called "mass increase" is relative.

 

Which means that that which causes the mass increase is still there

 

What causes the "mass increase" (apart from pop-sci articles) is known as "energy". And, as we have already seen, that is relative.

[elfmotat]

I don't understand why asking 'what causes something' is such a problem. You can ask it about all kinds of things and get a concrete answer, but when you ask it about motion it becomes a problem. Doesn't make sense to me.

 

When you ask "what causes X" in everyday circumstances, you're working under some framework in which you allow something to be true. Otherwise, you're perpetually asking "what causes the thing that causes X," "what causes the thing that causes the thing that causes X," etc. And eventually you run into the same kind of boundary you've encountered here: you're asking questions to which there are no testable answers. And if something isn't testable, it's not science - it's philosophy. You should watch the video Strange posted again, if you haven't already: https://www.youtube.com/watch?v=wMFPe-DwULM .

 

 

Of course I don't accept it. It implies science knows everything there is to know about motion. Why would that be the case? How could you possibly know that? Because there's no need? According to what? Equations that describe some behavior that we see?

 

I don't understand how you're coming to the conclusion that "science knows everything there is to know about motion." Of course that's not true. What we do know is that Newton's laws work, the principle of relativity works, special relativity works. "Why" they work is metaphysics. You either accept that they work (until experiment shows otherwise) and move on, or you get bogged down in untestable "reasons" for why they might work.

 

 

But why would it be moving if no force has ever acted on it? It just does out of nowhere?

 

MOVING IN WHICH REFERENCE FRAME!?!?

 

This is what you're not getting. If there is some frame in which an object is at rest, then there are an infinite number of other equally valid frames in which it is NOT at rest. They are all valid descriptions of the same thing.

 

Yes, that's relative movement. But what about absolute movement? What's so strange about the concept of absolute movement?

 

There is no such thing as absolute movement! That's the problem! There is absolutely no test you can design to measure what your absolute velocity is. None at all. Because it doesn't exist. It's not defined. There's no such thing. I don't know how many more ways I can say it.

 

 

Motion causes an object to gain mass, right? I assume this mass increase doesn't get undone because something appears to be motionless. Which means that that which causes the mass increase is still there.

 

Under an outdated definition of "mass" (called relativistic mass), this is true. But its gain in mass is only relative to some other observer. Relativistic mass is really just the total energy, and we've already established that energy is frame-dependent.

Edited November 6, 2014 by elfmotat

[Thorham]

When you ask "what causes X" in everyday circumstances, you're working under some framework in which you allow something to be true. Otherwise, you're perpetually asking "what causes the thing that causes X," "what causes the thing that causes the thing that causes X," etc.

Yes, but when do you stop asking?

 

And eventually you run into the same kind of boundary you've encountered here: you're asking questions to which there are no testable answers.

Is it really not testable, or do we simply not know how to test it yet? If it's truly and absolutely untestable, then there is indeed no point, but can you be sure that these things really are untestable? How do you know what is truly untestable?

[elfmotat]

Yes, but when do you stop asking?

 

You can stop whenever you like. Just know that once you've left the realm of what's testable you're no longer doing science.

 

 

Is it really not testable, or do we simply not know how to test it yet? If it's truly and absolutely untestable, then there is indeed no point, but can you be sure that these things really are untestable? How do you know what is truly untestable?

 

Your question is about "why" the laws of physics are what they are. That's untestable, by every conceivable definition of the word. You can ask "how is it we know that there's no such thing as absolute velocity." The answer, of course, is that we've done a bunch of tests and there is zero evidence of any preferred frame! But when you ask "why" it should be that way, there's no way to answer.

Edited November 6, 2014 by elfmotat

[MigL]

Please don't make elfmotat yell again .

Nobody likes it when he's angry !

 

Are you moving as you read this question, Thorham ?

If you can ( intelligently ) answer that question without reference to another object or location then you have finally found absolute motion. Nobody else ever has because it doesn't exist.

If you can't, you only have relative motion, so suck it up and move on.

 

Almost two pages of this drivel is making my teeth hurt.

Edited November 6, 2014 by MigL

[davidivad]

My question is, does time have a speed? could events be going along faster in different places in the universe? can it be speed up or slowed down?

time happens at the speed of light.

it is a field.

the angle of motion so to say...

Edited November 7, 2014 by davidivad

[michel123456]

Yes relativity is baffling.

In this case, Galilean Relativity. Not even Einsteinian.

 

 

 

 

MOVING IN WHICH REFERENCE FRAME!?!?

 

This is what you're not getting. If there is some frame in which an object is at rest, then there are an infinite number of other equally valid frames in which it is NOT at rest. They are all valid descriptions of the same thing.

There is no need to become angry.

The same people who say that velocity is relative are the ones who say that the velocity of light is absolute.

Don't be surprised that people don't get it just like that.

 

What is motion is a very good question.

To me, motion is a way to harvest energy.

Edited November 7, 2014 by michel123456

[swansont]

The same people who say that velocity is relative are the ones who say that the velocity of light is absolute.

Velocity is relative in Galilean systems, too.

[elfmotat]

There is no need to become angry.

Using caps lock and big font does not imply I was angry. It implies I was trying to drill home a point that I've been repeating for two pages now, without much effect.

[phyti]

Yes, but when do you stop asking?

 

 

Is it really not testable, or do we simply not know how to test it yet? If it's truly and absolutely untestable, then there is indeed no point, but can you be sure that these things really are untestable? How do you know what is truly untestable?

Motion is the behavior of multiple objects. It’s observing the change of positions relative to one of the objects selected as a reference. Obviously it is not an object property but a group property.

If an object wanders into the vicinity of Earth, it acquired its velocity at some time in the past, if we accept cause and effect. It could be a relic from planetary formation thousands of light years distant, but we have no way of knowing its history.

Yes, the propagation speed of light in space (ideal vacuum) is constant and independent of its source. It serves as an absolute reference for speed, as in the expression v/c used in SR. If we could set a marker at the spatial location of emission, we would have a fixed point of reference for subsequent calculations. Imagine finding a productive fishing spot and leaving a buoy (no anchor) at the site. The next day you return to the buoy. How do you know it’s the same spot? That’s the problem since light emission leaves no residue for the CSI.

If you analyze the physical phenomena in a moving test frame relative to a theoretical absolute static frame of reference, you discover the phenomena occur as if the test frame is not moving. Fascinating to discover but greatly simplifying analysis and application of rules of science. Eg., NASA can calculate an orbit without knowing the center of mass of our galaxy.

[Strange]

Is it really not testable, or do we simply not know how to test it yet? If it's truly and absolutely untestable, then there is indeed no point, but can you be sure that these things really are untestable? How do you know what is truly untestable?

 

You are the one making the claim: it is up to you to show that it is testable and then that there are tests that support your claim.

 

All the tests that have been done so far show that you are wrong.

[Thorham]

I'm still going to say that absolute speed does exist. The speed of light is absolute, so, what about the speed of a body relative to a photon from the photon's perspective?

 

I'm also not convinced that there can't be a system that causes motion to be possible, and that this is not measurable at all if it does in fact exists. That we can't measure it today means nothing, and that there's no reason to believe it does exist today also means nothing.

Edited November 10, 2014 by Thorham

[Strange]

I'm still going to say that absolute speed does exist. The speed of light is absolute, so, what about the speed of a body relative to a photon from the photon's perspective?

 

It doesn't really make sense to talk about speed relative to a photon but if you do then, because the speed of light is the same for all observers, everything is travelling at the speed of light relative to a photon. So not very useful, either.

 

 

I'm also not convinced that there can't be a system that causes motion to be possible

 

I still don't understand what the connection between a possible "system/mechanism for motion" and absolute motion is.

Edited November 10, 2014 by Strange

[elfmotat]

I'm still going to say that absolute speed does exist. The speed of light is absolute, so, what about the speed of a body relative to a photon from the photon's perspective?

 

I'm also not convinced that there can't be a system that causes motion to be possible, and that this is not measurable at all if it does in fact exists. That we can't measure it today means nothing, and that there's no reason to believe it does exist today also means nothing.

 

If you want to be a crank, fine, that's your decision. There is no "photon's perspective." Photons do not have rest frames.

[Thorham]

It doesn't really make sense to talk about speed relative to a photon but if you do then, because the speed of light is the same for all observers, everything is travelling at the speed of light relative to a photon. So not very useful, either.

But not from the photon's own perspective. It 'sees' everything else moving, but not itself. Things that are moving at different speeds as seen from some ordinary perspective, should also appear to be moving at different speeds from the photon's perspective. Because the photon can only move at one speed, you should see the absolute speed of everything else if you were the photon.

 

I still don't understand what the connection between a possible "system/mechanism for motion" and absolute motion is.

The connection is that if such a system exists, it may be possible to do direct measurements instead of relative ones, because that seems to be the problem: How do you measure things like this in an absolute way?

 

Photons do not have rest frames.

Eactly. They always move, and always at the same speed. That means that there is an absolute frame of reference. Of course we can't use that, so it currently remains unmeasurable by means that we know of. Doesn't mean it's not there.

[elfmotat]

Eactly. They always move, and always at the same speed. That means that there is an absolute frame of reference. Of course we can't use that, so it currently remains unmeasurable by means that we know of. Doesn't mean it's not there.

 

But it's not a frame of reference. Like I said, photons do not have rest frames.

[Strange]

But not from the photon's own perspective. It 'sees' everything else moving, but not itself. .

 

As noted, that perspective does not exist; it requires division by zero.

 

Things that are moving at different speeds as seen from some ordinary perspective, should also appear to be moving at different speeds from the photon's perspective.

 

The photon travels at the speed of light for every observer, whatever their relative speed (or direction). Therefore their speed relative to a photon is undefined (division by zero, remember).

 

Because the photon can only move at one speed, you should see the absolute speed of everything else if you were the photon.

 

Nope.

 

How do you measure things like this in an absolute way?

 

You can't.

 

They always move, and always at the same speed.

 

But not at any absolute speed. If you are heading east at half the speed of light (relative to Earth) and I am heading west at half the speed of light (relative to Earth) then we will both observe the same photon travelling at the speed of light. Therefore no absolute reference.

 

 

Doesn't mean it's not there.

 

If it is unmeasurable then it might as well not be there. Which is all that science cares about.

[Thorham]

But it's not a frame of reference. Like I said, photons do not have rest frames.

Aren't they at rest from their own perspective?

 

As noted, that perspective does not exist; it requires division by zero.

Is that relevant? It seems so simple: If something appears to be moving at the speed of light from the photon's perspective, then it's not moving at all. If it appears to be moving at a quarter of the speed of light according to the photon, then it's moving at three quarters of the speed of light. Seems to make sense.

 

The photon travels at the speed of light for every observer

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?

 

Nope.

So, what would you see then?

 

You can't.

How do you know this?

 

But not at any absolute speed. If you are heading east at half the speed of light (relative to Earth) and I am heading west at half the speed of light (relative to Earth) then we will both observe the same photon travelling at the speed of light. Therefore no absolute reference.

It's not about what we see, it's about what the photon would see.

 

If it is unmeasurable then it might as well not be there. Which is all that science cares about.

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

[elfmotat]

Aren't they at rest from their own perspective?

 

Photons do not have a perspective because there is no valid reference frame in which they are at rest. Why do you always make me repeat myself? Am I going to have to say this 4-5 more times? I'll do it in advance, just to get it out of the way: they don't have perspectives. They don't have rest frames. You can't talk about the experience of a photon. Time does not pass for anything moving at c. There is no photon perspective. End of story.