Does velocity really dilate time?
- Thread starter Uclock
- Start date
Physical things like gravity and acceleration can't dilate time because time is just a concept.
Physical things can only affect other physical things (like clocks).
Mental things like time can be affected by thoughts (like emotions).
For example if you're bored time goes slow, and if you're having fun time goes fast.
Physical things can only affect other physical things (like clocks).
Mental things like time can be affected by thoughts (like emotions).
For example if you're bored time goes slow, and if you're having fun time goes fast.
Having watched a programme on the failures of GR about four years ago it was said that the GPS had an accuracy drift which becomes worse after each adjustment although I have not been able to find out if this is true or not. Even so surely the GPS receivers have an element of acceleration involved in the form of their position inside the gravity field and there centripetal acceleration due to the rotation of the Earth.
Tony
Tony
What program, what failures?
GPS takes into account relativistic effects from both velocity and gravity. It is literally a relativity laboratory in space.
Janus58
Valued Senior Member
It hard to do an experiment where no accelertion is involved, But experiments have been done that show that accleration in of itself does not affect Time dilation.
A simple one is the centrifuge experiment, where you place a radioactive sample in a centrifuge, spin it up to a high speed, hold it there for a while, and then compare its decay to a control sample.
The advantage of this is that you can use it to determine what, if any effect acceleration has on time dilation. You can do this by changing the radius of the centrifuge between experiments. Thus you you can give two samples the same radial velocity but different centripetal acelerations, or the same centripetal acceleration and different radial velocities.
What these experiments have shown is that the decay rate of the sample is a function of the radial velocity of the sample alone, and that varying the acceleration has no effect.
Yorda
So you are saying that Einstein is wrong when stating that gravity is a distortion of spacetime, is that correct?
I know he believed the arrow of time was a psychological phenomenon in the sense of the mind creating order but I think he was correct when viewing gravity as a distortion of space and time.
Tony
So you are saying that Einstein is wrong when stating that gravity is a distortion of spacetime, is that correct?
I know he believed the arrow of time was a psychological phenomenon in the sense of the mind creating order but I think he was correct when viewing gravity as a distortion of space and time.
Tony
Janus58
Valued Senior Member
No, because, gravitational time dilation is related to a difference in gravitational potential not gravitational force.
Thus, if you put an observer on the centrifuge, and through the equivalence principle, he concluded that the centripetal acceleration was due to an outward acting gravitational field,( to do this he would have to assume that the centrfuge was not spinning.) he would determine that the center of the disk was higher in the field and at a higher gravitational potential. How much of a difference depends on two factors, the distance to the center and the gravitational gradient. (One way to think about it is as how much work it it would take to lift a given weight from the observer's position to the center. Lifting a mass a long distance against a weaker gravitational force can take the same work as lifting it against a stronger force for a shorter distance. In these two cases the gravitational potential are equal.)
Thus you could have two observers on two different centrifuges spinning with different rpms, one far from the center and with a shallow gravitational gradient and one closer to the center with a steeper gradient, and they would measure the same gravitational potential between observer and center and both would measure the same gravitational time dilation even though they feel different gravitational forces.
To an outside observer not spinning with the centrifuges, each of these observers would have the same radial velocity and thus the same time dilation even though they undergo different accelerations.
Janus58
But the equivalence principle states that all accelerated reference frames possess a gravitational field then this must mean the more acceleration the deeper in the gravitational field for the equivalence principle to hold true.
Gravity itself is not a force it is a distortion of spacetime so according to the EP any object under acceleration will posses a distortion of spacetime and the greater the acceleration the greater the distortion. Any kind of g-load will create gravitational time dilation.
The equivalence principle has nothing to do with velocity other than angular velocity which is everything to do with acceleration and I’m still waiting for you to point me in the direction of these experiments so I can confirm your view of the EP.
Tony
But the equivalence principle states that all accelerated reference frames possess a gravitational field then this must mean the more acceleration the deeper in the gravitational field for the equivalence principle to hold true.
Gravity itself is not a force it is a distortion of spacetime so according to the EP any object under acceleration will posses a distortion of spacetime and the greater the acceleration the greater the distortion. Any kind of g-load will create gravitational time dilation.
The equivalence principle has nothing to do with velocity other than angular velocity which is everything to do with acceleration and I’m still waiting for you to point me in the direction of these experiments so I can confirm your view of the EP.
Tony
James R
But there is an element of acceleration involved here. Muon decay is caused be high energy cosmic rays impacting air molecules producing pions which decay into muons. The point here is they have been accelerated by the impact and experience deceleration through the atmosphere so not only velocity is involved.
Tony
But there is an element of acceleration involved here. Muon decay is caused be high energy cosmic rays impacting air molecules producing pions which decay into muons. The point here is they have been accelerated by the impact and experience deceleration through the atmosphere so not only velocity is involved.
Tony
i doubt he seriously thought that things have weight because "spacetime" is distorted. space can't be distorted because it doesn't consist of anything. magnetism doesn't distort space+time, so why would gravity. they're the same thing.
Uclock: acceleration doesn't cause time dilation. Really. You can understand this if you run the Twin's Paradox thought-experiment twice over. On the first run twin A travels for one light year before he turns back. On the second run twin A travels for two light years before he turns back. In both cases the acceleration is the same, the only difference is the duration of the coasting phase. And this is what determines the differential ages of the twins.
What actually causes this time dilation is a change in c. We can never measure c to be anything other than 300,000km/s. Hence we tend to think of c as a rock-solid constant. But when you understand relativity to the full, and realise how light defines our distance and our time, you will understand that c is not in truth an absolute constant at all. The twin who aged less aged less because his c was lower than that of his twin, but he didn't notice it. See TIME EXPLAINED and GRAVITY EXPLAINED for details.
Others here may beg to differ. They can assert that I'm wrong, but they cannot prove me wrong. I dare say that at some point in the future some of them will be teaching this in schools. I imagine it will be called Relativity++. And that's what you call a challenge.
What actually causes this time dilation is a change in c. We can never measure c to be anything other than 300,000km/s. Hence we tend to think of c as a rock-solid constant. But when you understand relativity to the full, and realise how light defines our distance and our time, you will understand that c is not in truth an absolute constant at all. The twin who aged less aged less because his c was lower than that of his twin, but he didn't notice it. See TIME EXPLAINED and GRAVITY EXPLAINED for details.
Others here may beg to differ. They can assert that I'm wrong, but they cannot prove me wrong. I dare say that at some point in the future some of them will be teaching this in schools. I imagine it will be called Relativity++. And that's what you call a challenge.
Yet, one of the primary postulates of Special Relativity is that c IS a constant. Seems like you need to revisit your understandings.
Michelson and Morley.
Visions of grandeur?
No, you need to revisit your understanding. Really. Yes the constant c is a postulate for Special Relativity, and that's fine because c is always measured to be constant. But if you undergo time dilation, your seconds are different so your c, the c that defines your seconds, must be different too. It's crushingly simple. There's no conflict here with Michelson/Morley. They got a negative result for aether flow, but that's not the same thing as the beautiful subtlety of a constant c that actually isn't constant. See this quote:
"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)." Albert Einstein (The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity)
I thought Relativity++ was rather a nice name, akin to the programming language c++. The point is that c changes. LOL, it isn't spacetime that's curved, it's c that's curved, c isn't flat.
"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)." Albert Einstein (The General Theory of Relativity: Chapter 22 - A Few Inferences from the General Principle of Relativity)
I thought Relativity++ was rather a nice name, akin to the programming language c++. The point is that c changes. LOL, it isn't spacetime that's curved, it's c that's curved, c isn't flat.
"We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity ; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)."
:shrug:
Thanks dav. I think we can be fairly sure I've got something wrong. But I don't think I've got it all wrong. What I really need is some considered intelligent feedback instead of simplistic axioms and a refusal to consider the issues seriously. Then we'll have a better idea. Meanwhile it exercises our curiosity and it's fun, and I guess that's why we're all here.