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Post by abacus9900 on Oct 5, 2010 13:14:43 GMT 1
It's quite simple. Clocks run faster the further away they are from a massive body such as the earth, which is why the clocks on-board GPS satellites have to be adjusted to 'align' with clocks on earth. If it's all an invention of the human mind then so is gravity and mass, etc.
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Post by carnyx on Oct 5, 2010 14:20:22 GMT 1
abacus9900
You will find the definition of a clock in Post 1.
I suspect you are geting tangled up with the idea that time-as-a-flow exists independently as a physical thing, whereas it is a metaphysical construct. Rather, the time 't' in physics is a relative measurement between two physical processes, and involves the detection of the movement of mass, which is as we know is affected by the force of gravity.
In other words, ask yourself what your clock is actually measuring, and how is it doing it? And how would you test and calibrate it? (i.e. how do you know that the intervals between ticks are equal, and of the correct length?)
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Post by speakertoanimals on Oct 5, 2010 15:28:59 GMT 1
Rather, the time 't' in physics is a relative measurement between two physical processes, and involves the detection of the movement of mass, which is as we know is affected by the force of gravity. Except you have still mixed up the effect of gravity on a mass (an additional force), with the actual effects of gravity on time and distance. The whole point being, the observed effects DON'T depend on gravitational strength per se, but on gravitational potential, and you still get an effect between clocks even when the gravitational force on each is EXACTLY the same. Granted, before we had done the experiments, it was a question -- what effects clocks/all physical processes, differences in gravitational field strength, or differences in gravitational potential. It turned out to be the later, according to experiment. And actually there are perfectly good reasons why it should be potential, related to conservation of energy, and it applies in a very general way, not just to einsteins theory of gravity. [/quote] |
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Post by abacus9900 on Oct 5, 2010 15:56:45 GMT 1
abacus9900 You will find the definition of a clock in Post 1. I suspect you are geting tangled up with the idea that time-as-a-flow exists independently as a physical thing, whereas it is a metaphysical construct. Rather, the time 't' in physics is a relative measurement between two physical processes, and involves the detection of the movement of mass, which is as we know is affected by the force of gravity. In other words, ask yourself what your clock is actually measuring, and how is it doing it? And how would you test and calibrate it? (i.e. how do you know that the intervals between ticks are equal, and of the correct length?) Well, we could have a philosophical discussion about the fundamental nature of time but wouldn't that be rather inappropriate on a science board? The problem is, once you start questioning the philosophical foundations of measurement you encounter difficult paradoxes. |
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Post by abacus9900 on Oct 5, 2010 16:18:41 GMT 1
What she's referring to is the gravitational potential, which is a measure of the stored enegy in an object which is a direct measure of the amount of energy required to place an object in a given position above the earth. The original energy required had to oppose the gravitation force, therefore, gets stored in an object and when released, such an object falls towards the earth by expending kinetic energy.
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Post by carnyx on Oct 5, 2010 16:38:12 GMT 1
@sta
"and you still get an effect between clocks even when the gravitational force on each is EXACTLY the same."
This is a fantastic statement! Do you mean that the clocks themselves have a mutual gravitational attraction to each other? If so, you'd be right. But you'd be wrong if you thought that they were both at places where they weighed the same.
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Post by olmy on Oct 5, 2010 16:55:33 GMT 1
No, Newton's laws do not explain time dilation. Don't you think some of the many people who have studied this might of noticed, if they did?Well. Einstein, for one. What!? Einstein introduced a different theory - that's what we are talking about! Newton's laws do not explain time dilation. In any event, I already gave you a simple counterexample, in which the measurement of time is not affected by the strength of gravity, according to Newton's laws.Now firstly I hope you agree that Newton's idea of the force of gravity as a function of the inverse of the square of distance ( F= 1/D-squared) between masses ... is central to his theories? Your link took me to a very nice picture of a weight on a spring. Now, we need to find out the interval 't' of the vibration, so we have to use a fixed point to measure when the weight is at a certain point, so we can measure the time interval when it cycles back to that point. Then, we can see if 't' changes with changes in the local gravitational field. As gravitational changes can be simulated by putting the oscillating bob in a box, and accelerating it. We could do this simply by attaching it to the rim of a wheel, and rotating the wheel at a fixed speed. We will see a delay in the interval 't', as the bobweight appears to have become heavier. And as you say, the 'starting point' would have shifted. With our measuring system this corresponds to a change of 't' ... of an amount proportional to the change in local 'g'. We would have detected a slowing of our clock by a certain amount. And, if we bring the wheel to a halt, the clock would regain that lost time. If we accelerated the wheel, thereby increasing the local gravity field, then we should see that change in 't' repeated at every cycle, which is in effect a steady rate of phase-change, which is a de-facto a change in frequency, and so, our measured time. Our clock would then appear to be running slower and slower, in proportion to the rate of change of the local gravitational field. Good grief, you haven't got a clue how to do this simple calculation, have you? You can't even do this and you expect people to listen to your pet notions about time that disagree with all the evidence!? You need to apply Newton's second law and solve the differential equation (or just note that it is in a standard form). The period (using the same simplifications that gave you the one for the pendulum) is given by 2 pi times root m/k - where m is the mass and k is the spring stiffness. It does not include the acceleration due to gravity - so the whole basis of your 'argument' is gone. Sorry. |
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Post by Progenitor A on Oct 5, 2010 16:56:40 GMT 1
Well STA's insitence that it is the difference in gravitational potential rather rather than the difference in gravitaional field strength that causes gravitaional time dilation is contradicted by a couple of University Cosmology departments:
Toronto University
Einstein's General Theory of Relativity predicts that clocks in a gravitational fields run slow compared to clocks not in gravitational field, and that the stronger the gravitational field the slower the clock runs.
Cambridge University
T’=T(1 + F/c2)
where T' = dilated time
T= reference time
F= gravitational field strength
c= speed of light
Thus if F is a weak field, little time dilation occurs
If F is a strong field then more dilation occurs
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Post by eamonnshute on Oct 5, 2010 17:26:44 GMT 1
Wiki gives the formula for gravitational time dilation outside a non-rotating sphere here: en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphereThe amount is approximately proportional to M/r. Saturn is 95 Earth masses, and its diameter is 9.5 times that of Earth (conveniently). So the time dilation is greater by a factor of 95/9.5 = 10, despite the similar surface gravity. So the time dilation does not depend on the acceleration due to gravity. |
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Post by carnyx on Oct 5, 2010 17:47:11 GMT 1
abacus9900"Well, we could have a philosophical discussion about the fundamental nature of time but wouldn't that be rather inappropriate on a science board?" Actually, Einstein didn't think so. His relativity refers to the essential relativity of physical time. The 't' in physics can ONLY be a count of successive events in process A, relative to the counts of successive events in process B. And as an event involves the displacement of mass in some way, and as all mass is affected by gravity (there being no shield from it), then all events must be affected by gravity. So, if we change 'g' for ONE of our processes, we will see a change in 't'. Note that if we change 'g' for both processes (or clocks) there will be no change to measured 't' And, as Newton worked out that g changes as the inverse square of distance, we can work out the relative differences in g, and so the relative changes in 't'. However in practical terms they are negligible, and people got to the moon without bothering to correct for them
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Post by abacus9900 on Oct 5, 2010 18:23:46 GMT 1
abacus9900"Well, we could have a philosophical discussion about the fundamental nature of time but wouldn't that be rather inappropriate on a science board?" Actually, Einstein didn't think so. His relativity refers to the essential relativity of physical time. The 't' in physics can ONLY be a count of successive events in process A, relative to the counts of successive events in process B. And as an event involves the displacement of mass in some way, and as all mass is affected by gravity (there being no shield from it), then all events must be affected by gravity. So, if we change 'g' for ONE of our processes, we will see a change in 't'. Note that if we change 'g' for both processes (or clocks) there will be no change to measured 't' And, as Newton worked out that g changes as the inverse square of distance, we can work out the relative differences in g, and so the relative changes in 't'. However in practical terms they are negligible, and people got to the moon without bothering to correct for them I'm not sure if you are referring to 'quantized' events in the context of this discussion, are you? What I mean is that time or gravity, etc. can be considered as separate events, rather than a continuous process, as proposed in classical physics. This would bring in quantum theory which has found to be correct but, so far, poorly understood. It does appear that for future progress in physics to take place, quantum mechanics needs to be developed much more, but is this what you are really alluding to? |
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Post by Progenitor A on Oct 5, 2010 18:28:06 GMT 1
Wiki gives the formula for gravitational time dilation outside a non-rotating sphere here: en.wikipedia.org/wiki/Gravitational_time_dilation#Outside_a_non-rotating_sphereThe amount is approximately proportional to M/r. Saturn is 95 Earth masses, and its diameter is 9.5 times that of Earth (conveniently). So the time dilation is greater by a factor of 95/9.5 = 10, despite the similar surface gravity. So the time dilation does not depend on the acceleration due to gravity. You are simplifying things here somewhat. The instantaneous acceleration due to gravity on the surface of Saturn and the earth are approximately equal, but the local strength of the gravity fields vary enormously, the rate of change of acceleration on Saturn is greater than on Earth -remember that a gravitational field is characteriused by the rate of change of acceleration - so indeed the time dilation does depend on the gravitational field strength and how it varies. Who would you believe Wilkipedia of Cambridge University Department of Cosmology? |
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Post by eamonnshute on Oct 5, 2010 18:44:45 GMT 1
You are simplifying things here somewhat..... Who would you believe Wilkipedia of Cambridge University Department of Cosmology? If the formula on Wiki is oversimplified then please give us the correct formula. Ask Cambridge, if they use a different one. Or a physicist at Oxford University, such as SpeakerToAnimals. |
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Post by Progenitor A on Oct 5, 2010 18:58:21 GMT 1
You are simplifying things here somewhat..... Who would you believe Wilkipedia of Cambridge University Department of Cosmology? If the formula on Wiki is oversimplified then please give us the correct formula. Ask Cambridge, if they use a different one. Or a physicist at Oxford University, such as SpeakerToAnimals. But I have given you the Cambridge provided formula I suppose interpretation comes into play Personally I specificaly avoid Wiki. |
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Post by eamonnshute on Oct 5, 2010 19:08:01 GMT 1
But I have given you the Cambridge formula No you haven't. You have not said how F is calculated. And it is odd that you call it "field strength", not "acceleration due to gravity". Please provide a link to the website where you got your formula from. |
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