Interesting Theory

[ThePhoenix]

Saying that "Time" is a mirage is like saying that "Distance" is a mirage. Time is a measurable thing. All we've done is come up with our own measurements.

Well yes, it is. Relatively. But it's a yardstick that refuses to stay the same length. All our temporal measurements are based on our speed. If our galaxy, solar system, planet, etc. was moving faster or slower they would be different. Not much of a yardstick.

 

[Bushido216]

But there is still a governing rule for Time, the point is that we have to figure out what that is.

 

[ThePhoenix]

But there is still a governing rule for Time, the point is that we have to figure out what that is.

No there isn't. The theory of relativity says so. There is no absolute yardstick we have access to. We CANNOT measure our absolute velocity by any means, or the theory is toast. Since we cannot measure our absolute velocity we cannot measure absolute time.

 

[Bushido216]

What you're saying is that two experiments under the same exact circumstances will produce two separate results?

There must be a rule for determining the differences in velocity measured.

 

[ThePhoenix]

What you're saying is that two experiments under the same exact circumstances will produce two separate results?

There must be a rule for determining the differences in velocity measured.

Nope, that's the beauty of the theory of relativity. You see if light speed was constant, according to newtonian mechanics you'd have a universal yardstick. You could just say "Oh, look, the light heading at me is traveling 1.5. I must be traveling at .5 c. But this does not occur. Even if the spaceship is traveling at .5c (relative to earth) they will still measure the speed of light as c. That's the beauty of it.

Here's an illustration. Take diagram 1 at the bottom. That's the diagram of what an observer inside a train moving at .5c (half the speed of light sees). He measures the speed of that light from the time it takes to hit the mirror, and travel back. He gets c as the result for the speed of light.

Now take an observer standing outside the train (diagram 2). For him the light does NOT go straight. It goes in a roughly triangular shape thanks to the fact that the train moves as the light is moving. Therefore to him the light travels farther. He measures its speed and gets c.

Now here's where the fun comes in. The observers disagree on the distance, and agree on the speed. The equation for distance is d=vt. if velocity is constant, the t CANNOT be constant. Therefore time goes slower as you move faster. Both observers can state, with perfect correctness that they are at rest, and the other one is moving at .5 c, and BOTH are right. Both also get the same speed for light.

This is why the theory is the theory of relativity. There is no absolute except time.

 

[lucaspa]

Nope, that's the beauty of the theory of relativity. You see if light speed was constant, according to newtonian mechanics you'd have a universal yardstick. You could just say "Oh, look, the light heading at me is traveling 1.5. I must be traveling at .5 c. But this does not occur. Even if the spaceship is traveling at .5c (relative to earth) they will still measure the speed of light as c. That's the beauty of it.

Light speed is constant. That is the yardstick. As you say, you are traveling at 0.5c. No matter what your frame of reference, the speed of light in a vacuum is constant. What happens is that time slows for you relative to someone traveling 0.1c or 0.01c.

Now here's where the fun comes in. The observers disagree on the distance, and agree on the speed. The equation for distance is d=vt. if velocity is constant, the t CANNOT be constant. Therefore time goes slower as you move faster. Both observers can state, with perfect correctness that they are at rest, and the other one is moving at .5 c, and BOTH are right. Both also get the same speed for light.

Which is what makes the speed of light constant. v is constant but t changes.

There is no absolute except time.

What you just showed was that time wasn't absolute, but the velocity of light is absolute.

 

[ThePhoenix]

Light speed is constant. That is the yardstick. As you say, you are traveling at 0.5c. No matter what your frame of reference, the speed of light in a vacuum is constant. What happens is that time slows for you relative to someone traveling 0.1c or 0.01c.

I thought that was what I said. While lightspeed is a yardstick it's a yardstick that can't measure anything, since the length of the object it's measuring is relative to the observer. That part of the theory directly contradicts Newtonian mechanics, and overturns it by being correct

Which is what makes the speed of light constant. v is constant but t changes.

Yup

What you just showed was that time wasn't absolute, but the velocity of light is absolute.

GAH! I wrote that. My bad, that's what I get for writing at 1 AM.

 

[lucaspa]

I thought that was what I said. While lightspeed is a yardstick it's a yardstick that can't measure anything, since the length of the object it's measuring is relative to the observer. That part of the theory directly contradicts Newtonian mechanics, and overturns it by being correct

I know it's what you thought you said, but look at the first paragraph again. That "if light speed were constant" says the opposite. The velocity of light in a vacuum is constant. But as you say, length or time is not.

GAH! I wrote that. My bad, that's what I get for writing at 1 AM.

So it goes!

 

[ThePhoenix]

I know it's what you thought you said, but look at the first paragraph again. That "if light speed were constant" says the opposite. The velocity of light in a vacuum is constant. But as you say, length or time is not.


So it goes!

Oops, I have to second my "That's what I get for writing at 1 AM." What I meant was that under Newtonian mechanics, if the speed of light was constant it would provide a universal yardstick, which is how people often come to think of the speed of light as some yardstick that you can measure speed by. It's kind of a conflation of newtonian mechanics and the theory of relativity.

 

[lucaspa]

Oops, I have to second my "That's what I get for writing at 1 AM." What I meant was that under Newtonian mechanics, if the speed of light was constant it would provide a universal yardstick, which is how people often come to think of the speed of light as some yardstick that you can measure speed by. It's kind of a conflation of newtonian mechanics and the theory of relativity.

There you go. And it's what killed the aether. If light were being transmitted thru a medium, then the speed of light would be slightly different if you were measuring it in the direction the earth moves or away from the earth moves. These were the Michelson-Morely experiments.

Instead, the velocity stays constant but the wavelength changes. Doppler effect.

OTOH, can't we all measure our speed by a fraction of c? And you can get your fraction by watching the shift of the hydrogen emission bands, for instance? After all, isn't that how we calculate the recession of distant galaxies?

 

[ThePhoenix]

There you go. And it's what killed the aether. If light were being transmitted thru a medium, then the speed of light would be slightly different if you were measuring it in the direction the earth moves or away from the earth moves. These were the Michelson-Morely experiments.

Instead, the velocity stays constant but the wavelength changes. Doppler effect.

OTOH, can't we all measure our speed by a fraction of c? And you can get your fraction by watching the shift of the hydrogen emission bands, for instance? After all, isn't that how we calculate the recession of distant galaxies?

Well sure, you can, but that only gives you your speed relative to some star. Some star moving in a different direction would give you a different redshift. If you assume the stars to be stationary, then you can calculate your speed, but the expanding universe suggests rather strongly that they are not. Therefore, once again, all you have is a measure of your speed relative to some other object. The theory of relativity is named because of this. You can't measure your speed without some object that is non-moving in relation to you. For instance with a car that object is the earth. To get your speed you simply use the earth as a fixed point. It's not of course. Thus you get your speed relative to the earth.

 

[lucaspa]

Well sure, you can, but that only gives you your speed relative to some star. Some star moving in a different direction would give you a different redshift.

Yeah. You're right. It won't give you an absolute speed relative to light. Just the speeds of both of you relative to light.

However, there seems something wrong with this, somehow. Well, maybe not. Say I get up to 0.9 relative to earth and am overtaking a galaxy at 0.89c relative to earth. Time dilation would have me aging very slowly relative to earth ... but not to the inhabitants of the galaxy.

OK. You're right.

 

[ThePhoenix]

The much uglier problem is that a spaceship that passes the earth at .5c would be completely in the right when they thought that the earth was traveling past them at .5c - and both would agree on what age the travelers in the spaceship would be if they turned around and came back to earth. That one's a real puzzler took me days to figure out what path to take, and a good while to run the math behind it to see that I was right. My teacher was occasionally a real pain with his interesting questions.

 

[lucaspa]

I was thinking of Poul Anderson's book Tau Zero. It's a nice story built on a thought experiment. A spaceship has an accident and can't slow down. They are at a good fraction of c and thus their tau -- relative time dilation -- is very high. By the time they get it fixed the universe is so old that they decide to accelerate and ride out the Big Crunch (the book was written when the Crunch was still a viable idea; now we know it's false) and go thru the next Bang. That meant that they were going at .9999c relative to all the matter in the universe. But that would be due to the Crunch, not any absolute measurement.

 

[ThePhoenix]

I was thinking of Poul Anderson's book Tau Zero. It's a nice story built on a thought experiment. A spaceship has an accident and can't slow down. They are at a good fraction of c and thus their tau -- relative time dilation -- is very high. By the time they get it fixed the universe is so old that they decide to accelerate and ride out the Big Crunch (the book was written when the Crunch was still a viable idea; now we know it's false) and go thru the next Bang. That meant that they were going at .9999c relative to all the matter in the universe. But that would be due to the Crunch, not any absolute measurement.

Tau Zero eh? I'll add that to my reading list. That would be a lot of fun. Though there is the eventual problem with the spaceship: How do you slow down?

 

[lucaspa]

Tau Zero eh? I'll add that to my reading list. That would be a lot of fun. Though there is the eventual problem with the spaceship: How do you slow down?

Ramscoop and let the impacts of the interstellar hydrogen molecules do it. Also then use the hydrogen as fuel for the rockets for thrust.

 

[ThePhoenix]

Ramscoop and let the impacts of the interstellar hydrogen molecules do it. Also then use the hydrogen as fuel for the rockets for thrust.

What do they do about micrometeorites? An impact with a dime at .9999 c is probably the equivelent of a Hiroshima or two. Do they just outrun the meteorites? Hmm, a definate must-read.

 

[lucaspa]

What do they do about micrometeorites? An impact with a dime at .9999 c is probably the equivelent of a Hiroshima or two. Do they just outrun the meteorites? Hmm, a definate must-read.

The ramscoop shunts them aside if they want it to. I'm not sure Anderson dealt with all those details; he wrote this in the 1960s or so. He also didn't deal with the problem that when the universe rebounded there was going to be a small problem since the mass (and entropy) of the spaceship and crew were not included in the new Bang. Also, if spacetime contracted, where did the ship fly around during the singularity?