Does time have a speed?

[ajb]

I've heard that length has a flavour.

Is that a double entendre?

 

 

I am sure it has been mentioned somewhere here already, but theclosest to a speed of time would be something like

 

[math]\frac{d \tau}{dt}[/math],

 

which relates coordinate time and the proper time of an observer.

Edited November 6, 2014 by ajb

[elfmotat]

If what I mean by 'has no velocity' or 'has no kinetic energy' still isn't clear, then sorry, but I can't explain it any more clearly.

 

I know exactly what you're saying. All of my questions are driving at the same point: there are no special frames of reference. That's the central principle of relativity (it's actually called the principle of relativity). There is no absolute velocity, or kinetic energy, or time dilation. These things are only defined relative to a particular frame of reference. When you say "it has no velocity," you also need to specify with respect to what it has no velocity. Saying "it has no velocity" by itself is a meaningless statement.

I am sure it has been mentioned somewhere here already

 

Yes, I believe somebody did mention something like that:

 

I agree with Atheist's first post.

 

What you can do for massive particles is use the proper time to parametrise the paths of the particles. Thus you get the speed of proper time with respect to proper time is one!

 

Same thing for velocity really, "speed" depends on how you parametrise things. Only for massive particles can you do an affine transformation and bring this parameter to the proper time.

 

So, this also answers the question about photons experiencing time.

[Thorham]

I know exactly what you're saying. All of my questions are driving at the same point: there are no special frames of reference. That's the central principle of relativity (it's actually called the principle of relativity). There is no absolute velocity, or kinetic energy, or time dilation. These things are only defined relative to a particular frame of reference. When you say "it has no velocity," you also need to specify with respect to what it has no velocity. Saying "it has no velocity" by itself is a meaningless statement.

Then where does motion come from? What is it if it doesn't exists by itself?

Edited November 6, 2014 by Thorham

[elfmotat]

Then where does motion come from? What is it if it doesn't exists by itself?

 

I don't understand your question. Could you try rephrasing it?

[Thorham]

I don't understand your question. Could you try rephrasing it?

If motion if relative, then does it exist by itself as a property of mass?

[elfmotat]

If motion if relative, then does it exist by itself as a property of mass?

 

I don't know what this means either. It would probably be better if you asked more physical or mathematical questions. Questions about "existence" and "reality" tend to be very imprecise.

[Strange]

If motion if relative, then does it exist by itself as a property of mass?

 

Motion is not a property of mass. It is a measurement of change of position of one object relative to another. If there is a single thing, then there is no concept of motion or speed. If there are two things, then you can say that A is moving relative to B or that B is moving relative to A. There is not way in which you can say, in an absolute sense, that A is stationary and B is moving.

 

All motion, and therefore all velocity, is measured relative to something else. We measure the speed of cars relative to the road, ignoring the rotation of the Earth. We can measure the speed of the Earth around the Sun while ignoring the movement of the Sun through the galaxy. There is not such thing as the "real" speed of the car or the Earth; just what we choose to measure.

 

And, therefore the same is true of kinetic energy. The kinetic energy of an object purely depends on who measures it and how they define the velocity of the object.

Edited November 6, 2014 by Strange

[Thorham]

Motion is not a property of mass. It is a measurement of change of position of one object relative to another.

If it's not a property of mass, then what is it? There has to be something that causes it, right? You can't say that when only two objects exist and they're moving, that when one disappears, the other one stops moving just because it has become the only frame of reference. If things only move relative to other reference frames, then what is motion?

[Strange]

There has to be something that causes it, right?

 

Does there?

 

You can't say that when only two objects exist and they're moving, that when one disappears, the other one stops moving just because it has become the only frame of reference.

 

Although that is not a physically realistic scenario, I would say exactly that.

 

If things only move relative to other reference frames, then what is motion?

 

I don't think I can explain it any more clearly. Imagine you are in empty space with nothing else visible anywhere.

 

- Can you determine if you are moving or not? No.

 

Then another spaceship goes flying by. Your sensors tell you that it passed by at 500 mph.

 

- Can you tell if you are stationary and it flew by at 500mph? No.

- Can you tell if it was stationary and you flew past it at 500 mph? No.

- Can you tell if you both passed each other at 250 mph? No.

 

All you can measure is your relative speed.

 

Now that other spacecraft is gone.

 

- Can you determine if you are moving or not? No.

[elfmotat]

If it's not a property of mass, then what is it?

 

I thought his definition was rather clear.

 

 

There has to be something that causes it, right?

 

No. Set a ball down on the ground. Now get in your car and start driving at a constant velocity. Relative to you, the ball now has some velocity. Just like magic!

 

 

You can't say that when only two objects exist and they're moving

 

Relative to what?

 

 

that when one disappears

 

That can't happen, it violates physics. You can't use physics to describe situations which violate physics.

 

 

the other one stops moving just because it has become the only frame of reference.

 

Relative to what?

 

"Object" is not the same as "reference frame." A reference frame is just a coordinate system. There are an infinite number of coordinate systems you can use to describe a system with one object.

 

 

If things only move relative to other reference frames, then what is motion?

 

Again, what's wrong with Strange's definition?

[Thorham]

Does there?

Well, yes? Otherwise, how do things move at all? If there are no mechanics for motion, and it's not a physical property, then what is it? It doesn't seem unreasonable to assume motion is caused by something or is a physical property of mass.

 

All you can measure is your relative speed.

Of course, but does that mean that motion is something that only exists relatively? Because that seems to be what you're saying. I think that the fact that we can only measure motion relatively means that we don't get the whole picture.

Edited November 6, 2014 by Thorham

[elfmotat]

Well, yes? Otherwise, how do things move at all? If there are no mechanics for motion, and it's not a physical property, then what is it? It doesn't seem unreasonable to assume motion is caused by something or is a physical property of mass.

 

 

Of course, but does that mean that motion is something that only exists relatively? Because that seems to be what you're saying. I think that the fact that we can only measure motion relatively means that we don't get the whole picture.

 

As I said, it is better to stick to physical and mathematical questions. The type you're asking can't be answered by science. "Does motion exist when we can't measure it(?)" is a bit silly. It's one of those "if a tree falls in the forest..." type questions.

 

The point to take home is in bold. That's exactly what we're saying.

 

As far as us "not getting the whole picture" because there is no way to measure any absolute velocity, that's just a deep prejudice you have. It's a prejudice that exists because some of the aspects of relativity seem a bit contrary to common sense. But that's the way it works, and if you get a chance to learn the math one day you'll come to appreciate just how much more beautiful nature is this way. Thinking about it now, the idea of absolute velocity is really very ugly.

Edited November 6, 2014 by elfmotat

[Strange]

Well, yes? Otherwise, how do things move at all?

 

Newton's 3 laws. If something is in uniform motion, it will continue unless acted on by a force.

 

Of course, but does that mean that motion is something that only exists relatively? Because that seems to be what you're saying.

 

Yes. That is exactly what I am saying.

 

I think that the fact that we can only measure motion relatively means that we don't get the whole picture.

 

Then you will need some evidence to support that. All experiments to detect some absolute frame of motion have not done so.

 

As always with science, no one just assumes relative motion to be a fact; it is constantly being tested. (Search for tests of Lorentz invariance.)

Edited November 6, 2014 by Strange

[Thorham]

As I said, it is better to stick to physical and mathematical questions.

I am asking a physical question, namely, what is motion.

 

As far as us "not getting the whole picture" because there is no way to measure any absolute velocity, that's just a deep prejudice you have. It's a prejudice that exists because some of the aspects of relativity seem a bit contrary to common sense.

Is it? Can we measure the mechanics that enable movement? If not, then we don't get the whole picture.

 

But that's the way it works, and if you get a chance to learn the math one day you'll come to appreciate just how much more beautiful nature is this way.

No, that's not the way it works, because the universe isn't made of math. Our math describes the universe, but it doesn't say what 'stuff' is. That also makes us not get the whole picture.

 

Thinking about it now, the idea of absolute velocity is really very ugly.

The idea of some mechanic causing motion to be possible is ugly? Ugly or not, it seems rather essential for something like that to exist, or nothing would move at all.

 

Newton's 3 laws. If something is in uniform motion, it will continue unless acted on by a force.

And why is that? It doesn't just happen out of nowhere.

 

Yes. That is exactly what I am saying.

Then you're saying that that which cause motion would cease to exist. How can that be?

 

Then you will need some evidence to support that. All experiments to detect some absolute frame of motion have not done so.

Seems to me that to detect this you'd have to get to the fundamental mechanics of motion, that which cause it, or you'll never measure it.

[Strange]

And why is that? It doesn't just happen out of nowhere.

 

Inertia. But that is just another way of saying the same thing in a different way.

 

But even if there were some absolute motion, that wouldn't change Newton's three laws, so the question doesn't seem very relevant.

 

You are asking "why is the universe the way it is?" That is not a scientific question, it is a philosophical or religious question. There is no answer.

Edited November 6, 2014 by Strange

[elfmotat]

I am asking a physical question, namely, what is motion.

 

The fact that I addressed (or, rather, redirected) that question twice, specifically, in my previous reply should be a good hint that I wasn't referring to that one.

 

 

Is it? Can we measure the mechanics that enable movement? If not, then we don't get the whole picture.

 

Your question is nonsensical. I get the feeling you're just arguing for its own sake now.

 

 

No, that's not the way it works, because the universe isn't made of math. Our math describes the universe, but it doesn't say what 'stuff' is. That also makes us not get the whole picture.

 

That is indeed how relativity works, and it has passed every experimental test with flying colors for over a century.

 

 

The idea of some mechanic causing motion to be possible is ugly?

 

"Mechanic causing motion" makes no sense to me. The idea of picking out a preferred reference frame instead of having the symmetry we do is a very ugly thought indeed. Plus, it ruins everything based on relativity and its symmetries.

[Thorham]

You are asking "why is the universe the way it is?"

No, I'm not, I'm asking about the mechanics of movement. Yes, it's a 'why' question, but you can ask the same thing about chemistry. Why do two hydrogen atoms and one oxygen atom react to form a water molecule? They do that because of the way the building blocks of atoms work. These building blocks cause atoms to behave in that way. It's the same with motion.

 

That is not a scientific question, it is a philosophical or religious question. There is no answer.

There is indeed no answer to the question 'What is the true nature of reality?', and I'm not going to ask it, because it pointless.

 

I get the feeling you're just arguing for its own sake now.

Really, I'm not. I hate that.

 

That is indeed how relativity works, and it has passed every experimental test with flying colors for over a century.

Yes, it's how relativity works, but that only describes the behavior of the things we see in the universe.

 

"Mechanic causing motion" makes no sense to me. The idea of picking out a preferred reference frame instead of having the symmetry we do is a very ugly thought indeed. Plus, it ruins everything based on relativity and its symmetries.

So, then nothing causes motion? It just is? Like I asked before, if it's not a property of matter, and there are no mechanics that cause motion, then what is it? Why does it even exist at all? What's so ugly about that?

 

I push against a wall, and my hand doesn't go through it because the wall pushes back. Now how do we extend this line of thought to motion?

[swansont]

If motion if relative, then does it exist by itself as a property of mass?

 

Mass is a property, not a thing unto itself. Similarly, velocity is a property, which is always measured with respect to something else (an object or an abstraction such as a frame of reference).

 

I push against a wall, and my hand doesn't go through it because the wall pushes back. Now how do we extend this line of thought to motion?

 

Classically speaking, you will get an acceleration if you exert a net force on an object, such that a = F/m. If the object was at rest, it will begin moving. If it was already moving, some aspect of its motion will change. However, there is no distinction physics can draw between uniform motion and rest for a situation where relative motion exists— there is no experiment you can do to tell if you are moving or not, rather than something else moving.

[Strange]

No, I'm not, I'm asking about the mechanics of movement.

 

Then I have no idea what you are asking. What do you mean by "mechanics"? Do you imagine that when you throw a ball there must be little cogs and gears that keep it moving?

 

From Galilean relativity, basic dynamics and Newton's laws (v = ds/dt, s = ut + 1/2 at², f=ma, etc) through to general relativity, the concept and mathematics of motion are very well understood. What is puzzling you?

 

I push against a wall, and my hand doesn't go through it because the wall pushes back. Now how do we extend this line of thought to motion?

 

If you push and there is no wall, then the thing you push will move. And ... ?

[Thorham]

Then I have no idea what you are asking. What do you mean by "mechanics"? Do you imagine that when you throw a ball there must be little cogs and gears that keep it moving?

Not literally, but there must be something that enables 'stuff' to move, or can 'stuff' simply move?

 

Chemicals reacting -> caused by the arrangement and behavior of protons, neutrons and electrons.

'Stuff' moving -> caused by ???

 

You can ask the same question about fundamental particles. What makes them behave in the way that they do? For 'composite particles' like atoms it's easy. They behave that way because of how they're built up, and the behavior of what they're made of. For fundamental particles which aren't made of smaller particles, this isn't so straightforward.

 

You can ask it about other things as well. What causes a particle to have mass? What causes mass to curve space? Similarly, you can ask what cause particles to be able to move?

 

These seem like legitimate questions that may be perfectly answerable, even if we can't answer them today.

[Strange]

Not literally, but there must be something that enables 'stuff' to move

 

What "enables" it is the existence of space and time, I suppose. things can change their position in space over time. We label this phenomenon "movement" and quantify it as "speed".

 

I fail to see what is so baffling about that.

 

or can 'stuff' simply move?

 

Yes. Why not?

 

You can ask it about other things as well. What causes a particle to have mass?

 

For some particles, that is the Higgs mechanism.

 

What causes mass to curve space?

 

Now you are back to philosophical, why is the universe like it is, questions.

 

Similarly, you can ask what cause particles to be able to move?

 

The result of a force, or moving along geodesics in space time.

 

 

These seem like legitimate questions that may be perfectly answerable, even if we can't answer them today

 

They seem like ill-formed questions that have no answer.

 

http://www.youtube.com/watch?v=qjmtJpzoW0o

[Thorham]

What "enables" it is the existence of space and time, I suppose. things can change their position in space over time. We label this phenomenon "movement" and quantify it as "speed".

Yes, obviously. But has no one has asked what causes this movement? We have asked the same kind of question about other things, and over time we have been able to work out answers. What's different about motion?

 

Yes. Why not?

I don't know, but I do know that you don't get anywhere if you answer this kind of question with this answer for all known phenomena.

 

Before we knew how flight worked, you could just say that birds fly because they simply can. It's the easy answer that doesn't get you anywhere. We know why birds can fly now, so we know that such an answer is ridiculous in this case. That's why I keep hammering on the same question about motion. 'It just does' is simply not good enough.

 

At some point you're going to hit a wall. One example is existence itself. At some point things just existed. They didn't come from anywhere, they just were. But you just can't assume you've arrived at that point with the workings of what we see in the universe, or you may miss answers to answerable questions, and that's obviously unacceptable. The moment you stop asking questions, and assume it's just the way it is, is the moment scientific progress stops.

 

For some particles, that is the Higgs mechanism.

Right. Now why assume that there isn't something like that for motion, the curvature of space, or what causes magnetism to do what it does?

 

Now you are back to philosophical, why is the universe like it is, questions.

No, I'm not. At some point we may get stuck and just have to accept that something works they way it does just because it does. But is it wise to actually ever accept this? How do we know we have arrived at such a point? The moment you accept this, is the moment you stop investigating, because you're assuming that there isn't anything more to find.

[swansont]

Not literally, but there must be something that enables 'stuff' to move, or can 'stuff' simply move?

 

Chemicals reacting -> caused by the arrangement and behavior of protons, neutrons and electrons.

'Stuff' moving -> caused by ???

 

You can ask the same question about fundamental particles. What makes them behave in the way that they do? For 'composite particles' like atoms it's easy. They behave that way because of how they're built up, and the behavior of what they're made of. For fundamental particles which aren't made of smaller particles, this isn't so straightforward.

 

You can ask it about other things as well. What causes a particle to have mass? What causes mass to curve space? Similarly, you can ask what cause particles to be able to move?

 

These seem like legitimate questions that may be perfectly answerable, even if we can't answer them today.

 

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. (You have philosophy, i.e. metaphysics, if you find that helpful)

 

If you want a bit of something that sounds like philosophy, things can move because there is more than one frame of reference in the universe.

[elfmotat]

Not literally, but there must be something that enables 'stuff' to move, or can 'stuff' simply move?Chemicals reacting -> caused by the arrangement and behavior of protons, neutrons and electrons.'Stuff' moving -> caused by ???You can ask the same question about fundamental particles. What makes them behave in the way that they do? For 'composite particles' like atoms it's easy. They behave that way because of how they're built up, and the behavior of what they're made of. For fundamental particles which aren't made of smaller particles, this isn't so straightforward.You can ask it about other things as well. What causes a particle to have mass? What causes mass to curve space? Similarly, you can ask what cause particles to be able to move?These seem like legitimate questions that may be perfectly answerable, even if we can't answer them today.

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

 

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

[Strange]

 

But has no one has asked what causes this movement?

 

Yes.

 

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

 

GR answers it for more complex cases such as gravity; this is how we understand why gravity is not a force, things in free fall are not accelerating and the universe is expanding.

 

But I suspect that is not what you are asking. I don't know what you are asking.

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

 

You would think the notion of inertia was completely obvious.

 

But some ancient philosophers did think that there had to be a continuous application of force to make something continue in motion.

Edited November 6, 2014 by Strange