Relative Movement...

[Euracil]

I was thinking: all "day to day" movement we think of is just movement relative to the Earth, as if the Earth was stationary as we move on it. If we saw a line "trail" drawn from where we've physically truly been, we see a line shoot up into the sky or into the ground, because of the movement of the Earth, Sun, and Galaxy. But what would that "true" movement be relative to? And light--it's top, unchangeable speed--what is that relative to?

[OtherDalfite]

This isn't really a question that can honestly be answered. The closest thing we have to a non-moving reference is the milky way I believe. Even though that rotates still, we really have nothing else to judge. This brings up another question, how will we ever be able to tell if something isn't moving anyways? To us, the object would seem to be whisking by at several kilometers a second. We would just dismiss it as something else moving very fast and move on. We really can't tell if something isn't moving and won't be able to for a very, very long time.

[Monkeh]

The Earth rotates and circles the sun. The sun rotates and circles the centre of the galaxy. The galaxy rotates and circles the centre of our local group, (I don't know this, just guessing!), and the local group probably rotates and circles the centre of the cluster or super cluster in which we find ourselves and then that probably rotates and circles around the very centre of the universe in turn.

So I guess you should reference all movement in relation to the centre of the universe. We don't actually know where that is though AFAIK, so that's a problem.

If you stood still on the Earth's surface then your actual physical path through actual physical space would be all spirally I suppose. Sort of like a flattened stretched out spring which is bent towards a very large circle.

Sort of a little bit like this:

The speed of light, I suppose, is relative to it's point of origin.

All of this should not be taken as fact. In fact, nothing I ever commit to forum should be taken as fact. In fact, nothing anyone ever posts to a forum should be taken blindly as fact.

You're welcome for the life lesson

[OtherDalfite]

The Earth rotates and circles the sun. The sun rotates and circles the centre of the galaxy. The galaxy rotates and circles the centre of our local group, (I don't know this, just guessing!), and the local group probably rotates and circles the centre of the cluster or super cluster in which we find ourselves and then that probably rotates and circles around the very centre of the universe in turn.

So I guess you should reference all movement in relation to the centre of the universe. We don't actually know where that is though AFAIK, so that's a problem.

If you stood still on the Earth's surface then your actual physical path through actual physical space would be all spirally I suppose. Sort of like a flattened stretched out spring which is bent towards a very large circle.

Sort of a little bit like this:

-snip-

The speed of light, I suppose, is relative to it's point of origin.

All of this should not be taken as fact. In fact, nothing I ever commit to forum should be taken as fact. In fact, nothing anyone ever posts to a forum should be taken blindly as fact.

You're welcome for the life lesson

Actually, your guess was almost perfect about the orbital track we take. If you like OP, there is a very easy to use game that simulates N-Body physics, and can show you what path an object will take while on a spinning object moving through space.

http://dan-ball.jp/en/javagame/planet/

It may take a bit, but try and put a small moon around the blue object. Watch the orbital path that it leaves behind. This is basically the same as if you were standing on the rotating Earth as it orbited the Sun, only you would make larger "loops".

[gloowa]

The speed of light, I suppose, is relative to it's point of origin.

False.

Source: http://en.wikipedia.org/wiki/Theory_of_relativity

--------------------------------------------------------------------------

Concepts introduced by the theories of relativity include:

Measurements of various quantities are relative to the velocities of observers. In particular, space and time can dilate.

Spacetime: space and time should be considered together and in relation to each other.

The speed of light is nonetheless invariant, the same for all observers.

--------------------------------------------------------------------------

Speed of light is the same regardless of frame of reference.

That means if we had a rocket @ 99% of speed of light, and there was a flashlite aiming back of that rocket, light from that flashlight would still travel @ speed of light, not 1% of speed of light. Moreso, if we had another rocket travelling @ 99% of speed of light in opposite direction, light flashlight from the first rocket would still recrod as being @ speed of light on the second rocket.

[EDIT]

On original question. That's one of the questions i would like some physicist to answer.

I have trouble with following situation:

Let's say we have a torus in Earth orbit. The torus is rotating, so there is an outward force applied to object on outer surface inside torus (assuming object is stationary relative to torus surface).

Now.

How do the laws of physics "know" that it is rotating. Rotating relative to what?

Same situation, now the entire universe is just this torus. How do the physics "know" if it's rotating, if the only frame of reference is it's own?

Edited August 12, 2013 by gloowa

[OtherDalfite]

I have trouble with following situation:

Let's say we have a torus in Earth orbit. The torus is rotating, so there is an outward force applied to object on outer surface inside torus (assuming object is stationary relative to torus surface).

Now.

How do the laws of physics "know" that it is rotating. Rotating relative to what?

Same situation, now the entire universe is just this torus. How do the physics "know" if it's rotating, if the only frame of reference is it's own?

I'm by no means a physicist, but I can try and answer that to the best of my abilities.

We know it's rotating because it's easily visible. That, and you can feel the effects imparted by the rotation of the torus. According to our current knowledge of the laws of physics, it has to be rotating, because everything rotating around it wouldn't make sense, as it would basically make that torus the non-moving reference frame we need to decide. We take the guess it is rotating by outside view and comparison of it to it's parent body or the stars.

If you happen to mean that it isn't rotating, and that it matches the non-rotating reference frame, that wouldn't really follow the law of centripetal force.

[andrewas]

Motion is relative, but rotation is absolute. Every part of the structure is constantly accelerated as the rest of the structure haul it round. This is the case even if you put the torus in an empty spacetime and spin it.

[Monkeh]

If a torus was in an empty space time then there would be no force to act on it which could set it rotating and nothing to use as reference to decide if it was rotating or not. Would you still feel centripetal force sat on the edge of it...debatable, apparently.

If you time lapse the night sky you see the whole universe rotating around you. You appear to be the centre of everything. As does anybody anywhere in the universe doing the same thing.

A person floating in interplanetary space isn't moving anywhere. Someone comes floating out of the black and whizzes past waving. "They were moving fast" you think, "just as well I'm not moving or we might have collided". The other guy though, he's thinking THE EXACT SAME THING.

Not entirely sure where I'm going with this to be honest...I've managed to de-rail myself. Good job me.

[ecat]

Disclaimer: What I am about to say will not help at all, not just because I don't know what I'm talking about.

The speed of light is not relative to anything, the speed of light is a constant.

Two particles each travelling at the same near light speed. One is approaching from the east the other from the west. If you are equidistant between them then both will reach you at exactly the same time. This is allowed. The closing velocity of the two particles is greater than the speed of light, this is allowed as neither is travailing faster than the speed of light. Particle one does not 'see' particle two closing at faster than the speed of light because for that to happen 'something' would need to be travelling faster than the speed of light which is not allowed - kind of.

Pick one of the following two statements:

1) The universe has no centre.

2) You are the centre of the universe.

It doesn't matter which one you chose as both are true.

Two galaxies or clusters or super clusters, you can pick your own scale. Neither travelling at anywhere near the speed of light yet they may be diverging from each other at a speed greater than the speed of light. This is allowed. Since galaxy one cannot 'see' galaxy two there is no violation of relativity and since the divergence is caused by the compounded effect of the expansion of space, with no single volume of space expanding at a rate greater than light speed, no laws are broken.

Tehe. Science! It makes everything so clear

Edited August 12, 2013 by ecat

[gloowa]

I'm by no means a physicist, but I can try and answer that to the best of my abilities.

We know it's rotating because it's easily visible. That, and you can feel the effects imparted by the rotation of the torus. According to our current knowledge of the laws of physics, it has to be rotating, because everything rotating around it wouldn't make sense, as it would basically make that torus the non-moving reference frame we need to decide. We take the guess it is rotating by outside view and comparison of it to it's parent body or the stars.

If you happen to mean that it isn't rotating, and that it matches the non-rotating reference frame, that wouldn't really follow the law of centripetal force.

Yeah, that doen't work... you explain the cause (rotation) by using effect (outward force). But there has to be a cause first, then the effect can take place. So first, laws of physics need to "realize" that torus is rotating, then "cause" the outward force.

Yes, if there is an outward force, then it's safe to assume that torus is rotating, but taht force is relative to two variables - radius of torus (constant) and angular velocity. I have trouble with angular velocity, because even if we assume that torus is rotating around it's axis which is not rotating, then [the axis] is not rotating relative to what exactly? Aether?

[Diche Bach]

But actually it gets much worse

"...civilization is not something absolute, but ... is relative, and ... our ideas and conceptions are true only so far as our civilization goes."

F. Boas 1887

[gloowa]

But actually it gets much worse

F. Boas 1887

Well, it still can be even worse

[Diche Bach]

Well, it still can be even worse

Ah, true . . . true . . .

And yet, still worse yet . . . still

You literally couldn't make this stuff up . . .

Derrida's theories of Deconstruction first demonstrate that in a classical philosophical opposition readers are not confronted to the peaceful coexistence of a vis-à-vis, but rather with a violent hierarchy.[4] One of the two terms governs the other (axiologically, logically, etc.), or one of the two terms is dominant (signified over signifier; intelligible over sensible; speech over writing; activity over passivity; male over female; man over animal, etc). The deconstruction of the opposition, is to overturn the hierarchy at a given moment. To overlook this phase of overturning is to forget the conflictual and subordinating structure of opposition.[5]

[AngelLestat]

So I guess you should reference all movement in relation to the centre of the universe.

False, the universe has no center.

Each point of the universe is the center of the universe.. We are in the center of the universe from our view point.

There was another video that explain that a lot better, but i cant find it. You had a ballon, you paint some points on it. Then you put a paper on the surface so the tint mark the points, then you inflate the ballon and you repeat the process with a transparent paper.

Then you put the transparent over the first one and you make coincide any star that you choose, and no matter what is your choice, it will look like it is the center of the universe.

So, there is no center.

[K^2]

Motion is relative, but rotation is absolute. Every part of the structure is constantly accelerated as the rest of the structure haul it round. This is the case even if you put the torus in an empty spacetime and spin it.

It's more precise to say that acceleration is absolute.^* Rotation itself can be seen as relative due to symmetries, but because of accelerations involved you can always tell whether you are turning or not even without any references.

^* I really should mention Mach's Principle at this point. Mach's Principle states that all acceleration is relative to remote masses. So you couldn't tell the difference between you spinning or the universe being spun around you. Unfortunately, General Relativity, which is the best theory we have to explain anything to do with relative motion, violates Mach's Principle. According to General Relativity, acceleration is absolute and that's that.

I was thinking: all "day to day" movement we think of is just movement relative to the Earth, as if the Earth was stationary as we move on it. If we saw a line "trail" drawn from where we've physically truly been, we see a line shoot up into the sky or into the ground, because of the movement of the Earth, Sun, and Galaxy. But what would that "true" movement be relative to? And light--it's top, unchangeable speed--what is that relative to?

There is no "true" movement. All movement is relative. Even the speed of light limit is relative, which is why it's a local limit.

[Diche Bach]

False, the universe has no center.

Each point of the universe is the center of the universe.. We are in the center of the universe from our view point.

There was another video that explain that a lot better, but i cant find it. You had a ballon, you paint some points on it. Then you put a paper on the surface so the tint mark the points, then you inflate the ballon and you repeat the process with a transparent paper.

Then you put the transparent over the first one and you make coincide any star that you choose, and no matter what is your choice, it will look like it is the center of the universe.

So, there is no center.

Somehow this makes me imagine the scale of human perception as nothing more than a multiplication of that of a microorganism, aware through its simple chemo and light receptors of its immediate surroundings, but functionally incapable of actually comprehending any higher (or lower) scale of reality.

[GregoryNeal]

Gentlement, this is a very simple question to answer, based on Einsteins two postulates (which led to the development of Special Relativity: http://en.wikipedia.org/wiki/Postulates_of_special_relativity). There is no preferred frame of reference, there is no "non-moving" frame. We can only move relative to other frames, be it the Sun, Earth, or the can of Dr. Pepper sitting in front of me. As for the speed of light, it's speed is relative to everything, because in all frames light travels at c.