Time is not an absolute?

[Dory]

Dory, yes, time slows down (and distance decreases, V = D/T (and light speed is constant) relative to the speed you're traveling.

But this wouldn't make you age slower. You'd still age one year for every year that you lived. It's just that if someone leaves your frame of reference and come back, they might end up with a different calender than you - different day, different year, different clock.

To examine your super-spinny planet, lets give it a second frame of reference, another planet that is spinning at a normal pace that is nearby. Yes, the people on super-spin would age slower than the people on slow spin.

However, both of them would agree that super-spin was undergoing acceleration, so they'd both agree on what the time dilation should be.

P.S. Light doesn't get to have a point of view, for the same reason that it doesn't get to have a mass.

I think that whether photons have a mass in an issue of controversy, but I'll drop it.

I will say that physics has certainly become my chosen scientific field. I really, really, love it. I hope to see a lot of physics as I move through the mechatronics (practical engineer) degree.

Keep up the good fight...and thanks for the feedback, Grey, mistermack, that totally cleared it for me.

[mistermack]

Everything would change if there's a real frame of reference! The speed of light would have to be measured next to the universal frame of reference, not your personal frame of reference!

I don't agree. If there were a real frame of reference, you would not be able to detect any difference. Why would it affect time dilation?
If you can convert from every possible frame, to every other, then you can convert from every frame to the one real one. You would have no way of knowing it was the real one. So I don't think it would have the consequences you said.

[GreyICE]

Photons have a rest mass. That is to say, E = m*c^2, and since photons have energy, well, they have mass This does not act like matter, really:

http://www.springerlink.com/content/b87v628331668g2r/

It's ODD. And that's for my very HIGH tolerance for odd. However, due to mass increases, if they had a mass while moving, it would be infinite.

P.S. That one comes about because F = m*a. Since force is energy, and energy can be measured and agreed upon in all frames, constant force with constant mass would produce constant acceleration. However, constant acceleration would allow one to exceed the speed of light (just by gaining 1 m/s/s for more than 300 million seconds).

I don't agree. If there were a real frame of reference, you would not be able to detect any difference. Why would it affect time dilation?
If you can convert from every possible frame, to every other, then you can convert from every frame to the one real one. You would have no way of knowing it was the real one. So I don't think it would have the consequences you said.

Uh, are we in agreement on what a universal frame of reference is? A universal frame of reference is a frame of reference where we could make the statement "that frame of reference is not moving" in any other frame of reference. That's why it's universal - everyone agrees that it's not moving.

If it's so well hidden that no one can measure it, it's not a universal frame of reference, it's just a nonsense idea. "Prove there is no invisible pink unicorn," really.

[mistermack]

Uh, are we in agreement on what a universal frame of reference is? A universal frame of reference is a frame of reference where we could make the statement "that frame of reference is not moving" in any other frame of reference. That's why it's universal - everyone agrees that it's not moving.

If it's so well hidden that no one can measure it, it's not a universal frame of reference, it's just a nonsense idea. "Prove there is no invisible pink unicorn," really.

No, we're not in agreement. I mean a "real" frame of reference, in which everything ACTUALLY moves. How could everybody agree it's not moving? If you are moving relative to it, you would percieve it to be moving.
You work it out. If there was only one real frame of reference, that everything actually moved relative to, how could you know? Every frame would appear equally valid, because time dilation would correct exactly for the motion of that frame.

[GreyICE]

Everything does actually move. Every non-accelerating frame of reference is motionless. There is no 'actually motionless' frame of reference.

As for the universal frame of reference, it would work simply, and it was assumed to exist. All observers would agree there is some inherent property to being 'actually moving,' and that the universal frame did not possess that property. It was originally assumed to be that moving objects slowed down. They observed that things that moved tended to move slower and eventually stop. That which was not slowing down was 'actually stopped.'

But there are no properties that define if an object is moving, there is no such thing as 'actually moving,' and 'actually stopped.'

[mistermack]

Everything does actually move. Every non-accelerating frame of reference is motionless. There is no 'actually motionless' frame of reference.

As for the universal frame of reference, it would work simply, and it was assumed to exist. All observers would agree there is some inherent property to being 'actually moving,' and that the universal frame did not possess that property. It was originally assumed to be that moving objects slowed down. They observed that things that moved tended to move slower and eventually stop. That which was not slowing down was 'actually stopped.'

But there are no properties that define if an object is moving, there is no such thing as 'actually moving,' and 'actually stopped.'

That's the theory. And of course it works perfectly. But like I said, if there was a real frame, and things either moved, or were stationary relative to that, nothing would look any different, and it would be impossible to detect.

Relativity and time dilation are a result of the fact that we and our measuring tools are made of what we are trying to measure.
Imagine the speed of light was constantly changing. How could we detect the change? The time and distances we perceive would constantly change with it.
That's why, as far as we are concerned, the speed of light can NEVER change.

[Don't Panic]

Ever sit through a sermon? Felt like 20 years instead one hour? Time slowed down for you. (Now replace "subjective" with "relativistic" and you're as close as you'll get without exotic maffs.)

Einstein said it best:

Sit next to a pretty girl for an hour, it seems like a minute. Sit on a red-hot stove for a minute, it seems like an hour. That's relativity.

[eXcommunicate]

Relativity is something that seems unintuitive first, but once you "get it" then it clicks and it pretty much sticks with you (like riding a bike).

[GreyICE]

That's the theory. And of course it works perfectly. But like I said, if there was a real frame, and things either moved, or were stationary relative to that, nothing would look any different, and it would be impossible to detect.

Relativity and time dilation are a result of the fact that we and our measuring tools are made of what we are trying to measure.
Imagine the speed of light was constantly changing. How could we detect the change? The time and distances we perceive would constantly change with it.
That's why, as far as we are concerned, the speed of light can NEVER change.

That's a belief, like the Invisible Pink Unicorn. I can't comment, it's the wrong forum for that stuff.

[mistermack]

That's the theory. And of course it works perfectly. But like I said, if there was a real frame, and things either moved, or were stationary relative to that, nothing would look any different, and it would be impossible to detect.

Relativity and time dilation are a result of the fact that we and our measuring tools are made of what we are trying to measure.
Imagine the speed of light was constantly changing. How could we detect the change? The time and distances we perceive would constantly change with it.
That's why, as far as we are concerned, the speed of light can NEVER change.

That's a belief, like the Invisible Pink Unicorn. I can't comment, it's the wrong forum for that stuff.

I'm not surprised. It seems you've read a bit about relativity, but actually understood very little. Being able to repeat what you've read doesn't count for much.

[Ulven]

Imagine the speed of light was constantly changing. How could we detect the change? The time and distances we perceive would constantly change with it.

If you have two mirrors a given distance apart moving very fast relative to your absolute frame of reference and you have two light beams bouncing back and forth between the mirrors, parallel to the motion of the mirrors and out of phase in such a manner that when one beam hits one mirror, the second beam hits the other.

According to your theory, the two beams would have different velocities. Which of the two velocities would govern the time and distance that we perceive?

[mistermack]

If you have two mirrors a given distance apart moving very fast relative to your absolute frame of reference and you have two light beams bouncing back and forth between the mirrors, parallel to the motion of the mirrors and out of phase in such a manner that when one beam hits one mirror, the second beam hits the other.

According to your theory, the two beams would have different velocities. Which of the two velocities would govern the time and distance that we perceive?

I don't think I follow what you're getting at.
The speed of light applies to everything in the Universe. If it WERE to vary, that change would apply to everything in the universe. Of course I don't have a theory, I was just saying if.

[Ulven]

I don't think I follow what you're getting at.
The speed of light applies to everything in the Universe. If it WERE to vary, that change would apply to everything in the universe. Of course I don't have a theory, I was just saying if.

That's OK. I didn't follow what you were trying to get at either.

But, since you don't have a theory and you're just lightly tossing thoughts around, I'm not going to worry about it any more.

[hackenslash]

Relativity and time dilation are a result of the fact that we and our measuring tools are made of what we are trying to measure.
Imagine the speed of light was constantly changing. How could we detect the change? The time and distances we perceive would constantly change with it.
That's why, as far as we are concerned, the speed of light can NEVER change.

No. Relativity and time dilation are a result of the fact that there is an invariant quantity in play, namely s, which is the momentum four-vector. This is also why light always travels at the same speed, regardless of frame. Light is a bit misleading here, because it isn't light that is special, it's the speed itself.

s=t2+(x2+y2+z2), where t is time and where x,y and z are spatial vectors. s is always the same, meaning that travel through space reduces travel through time, and this quantity is something that all observers must agree on, regardless of inertial frame. Since light uses all of its momentum in the spatial dimensions, it doesn't experience time, hence it is the same speed in all inertial frames.

[hackenslash]

I meant to add to that that time is not an absolute, and nor is space, but spacetime is. That's the point of relativity.