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Post by carnyx on Oct 3, 2010 22:31:35 GMT 1
Time is relative, in the sense that it can only be measured as a number of successive events in a sequence, that are counted between two successive events in a separate sequence. And, as any device for the physical determination of an event involves the movement of mass, then all such 'clock' devices are ineluctably affected by gravity .. i.e. changes in the local gravitational field. A basic example is that of a pendulum. If you look at the equation for the time period between swings of a pendulum, ( T = root Length /g ) you can see that if the term for gravity is changed, then the time period of the pendulum is changed. As we know that gravity gets weaker the higher you go, then the pendulum at the top of a mountain will be slower than when it is at the bottom of a mine. And this effect of the local gravitational field on mass can be expanded to include ALL sensible processes of any description; physical, chemical and biological. The rates of all processes ( aka sequences of events) are affected by changes in the local gravitational field; for example from the single cell to the human brain, and so human thought itself. And so 'measured time' is a human artifact that is affected by local gravitational field, and so the whole idea of time-as-a-flow that exists independently, is metaphysics, and is not physically true. In other words 'time' in those physics and mathematical formulae, is an invention of the human mind, and does not actually exist other than as computational artefact. Maybe the invention of this kind of 'time' must rank as one of the major intellectual achievements of all time Comments please.
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Post by Progenitor A on Oct 4, 2010 7:41:08 GMT 1
As we know that gravity gets weaker the higher you go, then the pendulum at the top of a mountain will be slower than when it is at the bottom of a mine. Interesting, but shouldn't this be the other way around? Surely time slows down under the influence of gravity so that in black holes where gravity is very high , time slows right down (some consider gravity 'infinite' at a black hole so that time actually stops, but as usual infinity raises a few problems), and the clocks on the satellites for GPS are running faster than earth clocks, so adjustments must be made to the time difference in calculating position? Ah! Now I see (as usual your postings require careful reading) - your (t) is based upon the ratio (k/g) and as g gets smaller so (t) becomes larger and the clock runs slower. Hmmm....very interesting - perhaps the GPS satellites should have pendulum clocks with the length of the pendulum adjusted to compensate for the speeding up of non-pendulum time!
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Post by olmy on Oct 4, 2010 8:54:45 GMT 1
Why, oh why, are so many people so determined to think time was invented? We have a very, very, very well tested theory of space-time. Time is as real (or unreal) as space. Your simple hypothesis about gravity and the measurement of time breaks down even in mechanical systems. Take a spring oscillator.... upload.wikimedia.org/wikipedia/commons/9/9d/Simple_harmonic_oscillator.gifIt's period depends only on the spring stiffness. The strength of gravity only affects the equilibrium position... Time is affected by gravity and motion, we know exactly how it is (that theory again) and we use it in technology... www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.htmlThat is not to say that our current theory is the last word - it isn't. However, any new theory will need to duplicate the results of Relativity.
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Post by StuartG on Oct 4, 2010 10:49:04 GMT 1
As a lead off the gps page there was 'Consequences of Relativity Observers moving relative to each other: * Do not measure the same times. * Disagree on what events occur simultaneously. * Do not measure the same lengths of objects. * Do not measure the same masses for objects. ' If the gps sattelites were set up in exactly the same way at: The edge of our Solar System, say on the heliosphere Another star system would they work the same [with corrections]?
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Post by carnyx on Oct 4, 2010 11:11:21 GMT 1
Olmy, you are right to say that the sense is inverted; T being inversely proportional to g. A careless mistake on my part.
I will reiterate that it is only possible to measure the interval we call 't' between successive events of Process A, by counting up the intervening successive events of Process B. In other words, we have to have a 'Process B' and the means to detect its events, to start with.
And, as any device for the physical determination of an event involves the movement of mass, then all such devices are ineluctably affected by gravity .. and changes in the local gravitational field.
This goes for the detection (or observation) of any event, includting spring clocks, quartz clocks, and even biological clocks of all kinds. For example, GPS satellite clocks have to be corrected because they run more slowly in a weaker gravitational field.
And, as electromagnetic radiation is the highest reference process 'B' that we can detect events in, then our measurement of 'time' has a limit ...
As does our abilty to detect an event ....
And so our measurement of time, and length, and mass, share this limit. We cannot measure a smaller interval of time that photons let us; which determines the smallest distance, and the smallest mass we can measure, and indeed the fasted velocity we can measure.
And for our probings beyond these doors, quantum physics lives, as a set of ingenious inferences.
But it should be noted that our perceptual limits, those quantifcation ( e.g. quantum) limits, do NOT inhibit smaller particles, intervals, faster-than-light velocities, and smaller masses from existing. It is just that we can't measure (aka detect) them.
I repeat;
It is only possible to measure the interval between successive events of Process A, by counting up the intervening successive events of Process B. And, as any device for the physical determination of an event involves the movement of mass, then all such devices are ineluctably affected by gravity .. and changes in the local gravitational field.
This set of statements can be derived directly from contemplation of Newton's laws, including the idea of 'time dilation' as an artefact of the measurement process.
But in everyday life, it is handy to operate on the belief that the metaphysical idea of time-as-a-flow is physically true, as humans generally all live in gravitational fields of the same strength and so our watches and clocks tick at the same rate.
And I suspect there has been money made from the exploitation of the apparent paradox that can be created by conflating the physical, and the metaphysical concepts of 'time'.
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Post by olmy on Oct 4, 2010 11:27:07 GMT 1
Oh dear, we are dealing with blind faith again! This set of statements can be derived directly from contemplation of Newton's laws, which explains 'time dilation' as an artefact of the measurement process. 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? 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. Look, do you seriously think you are some sort of genius who has seen something, despite an obvious lack of basic knowledge, that has been missed by the best minds of the twentieth and twenty first centuries? Seriously? Grow up. I just don't understand the mentality of people who think that they can overturn modern science with no actual knowledge or understanding of it whatsoever.....
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Post by olmy on Oct 4, 2010 11:29:57 GMT 1
If the gps sattelites were set up in exactly the same way at: The edge of our Solar System, say on the heliosphere Another star system would they work the same [with corrections]? I'm struggling to understand the question here. Do the corrections work anywhere? Yes - if you take into account the local gravity and relative motion. There are very obvious practical problems with trying to locate a GPS system in the places you suggest.
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Post by StuartG on Oct 4, 2010 12:25:52 GMT 1
'I'm struggling to understand the question here.' Instead of aircraft, space craft were thought of [in the future] they might need the same - set the Tom-Tom for Mars or Pluto. That was all it was. Thanks
mod: to expand, a Solar Positioning System [SPS]. Problems, problems, there's always problems. Two craft are out the way [heliosphere] Voyager 10&11, Ibex is due. So it's possible to get there.
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Post by carnyx on Oct 4, 2010 12:44:57 GMT 1
olmyYou say; 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. Then you say; 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. So, Olmy, you said it in your phrase; The strength of gravity only affects the equilibrium position... Which is equivalent to a phase change, and so represents a change of time, even in a Newtonian world.
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Post by speakertoanimals on Oct 4, 2010 12:50:06 GMT 1
Just to point out, the original post repeats a misconception, that time is affected by the local strength of the gravitational field. This is totally wrong. In relativity, what effects time is not the gravitational field strength, but differing heights in a gravitational field -- hence we have a gravitational time dilation even in a totally UNIFORM gravitational field. And given that gravitational time dilation/gravitational redshift has been tested over GPS altitudes, over the height of a tower, and now over a height of 33cm: www.sciencenews.org/view/generic/id/63657/title/Everything_really_is_relativeWhich blows the first post right out of the water. Moral -- try to learn the BASICS of a subject, before trying to build some supposed alternative theory of time on it. Else you end up looking like a right idiot.
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Post by Progenitor A on Oct 4, 2010 13:16:31 GMT 1
Just to point out, the original post repeats a misconception, that time is affected by the local strength of the gravitational field. You're talking gibberish. The earth's gravitational field is local to the earth. As the GPS system demonstrates, that local field will determine the 'speed' of time dependent upon the position of a clock in that field. Where the field is weaker (at a greater distance from the centre) clocks run at a different speed compared to clocks nearer the centre where the field is stronger. GPS orbiting clocks run faster than earth-bound clocks.
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Post by carnyx on Oct 4, 2010 14:51:39 GMT 1
speakertoanimalsCan you explain what you mean here; ".....what effects time is not the gravitational field strength, but differing heights in a gravitational field -- hence we have a gravitational time dilation even in a totally UNIFORM gravitational field. And given that gravitational time dilation/gravitational redshift has been tested over GPS altitudes, over the height of a tower, and now over a height of 33cm:..." You seem to me to be contradicting yourself; and in your second statement you are in fact agreeing with Post 1. It is precisely because the local gravitational strength affects all types of time-measurement systems, that such results are obtained. I really need to understand what you mean by a uniform gravitational field strength, and its relationship with the gravitational strength measured at any point in that field.
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Post by speakertoanimals on Oct 4, 2010 14:55:39 GMT 1
You'd better go tell Einstein then ,because he said the same! What matter is differing height in a grvitational field (varying in intensity or not), NOT difference in the strength of the gravitational field per se. So, for stuff in orbit, have gravitational field itself varying with height, as well as height difference, but it isn't the variation in the field strength per se that does the job.
To see this, let's go back to einsteins original thought experiment. Suppose we have a lift in space, which someone pulls along by the rope and causes it to accelerate at a fixed rate. This is localy equivalent to a gravitational field, and in fact equivalent to a UNIFORM gravitational field, since acceleration is the same however klong we wait, by definition.
Now imagine a light signal leaving the bottom of the lift. When it reaches the top (which depends on the height of the lift), the top of the lift is now moving faster than the bottom was went the signal was sent (since the lift is accelerating in a direction the inhabitants would call up). Hence we have a velocity difference between the source and receiver, hence Doppler shift.
THe size of the shift depends on the amount of acceleration (the strength of the gravitational field), and the distance, hence in Newtonian term it depends on the difference in gravitational potential, NOT on the difference in the strength of the gravitational field itself. That is why we get GPS effects in orbit -- they are much higher, it isn't the fact that the strength of the gravitational field has decreased over that height, and indeed the Einstein gedanken experiment shows specifically that we would still predict an effect even if there were NO variation in gravitational field strength between the two clocks.
Height not strength, a common misconception, you should have checked your facts before trying to accuse me of talking gibberish yet again..............
Of course, for physical objects, being higher means the gravitational field is also that bit weaker as well, but it isn't this weakening of the gravitational field that has the effect, although you have to include it in your calculations for the difference in gravitational potential if it is significant over the height considered.
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Post by carnyx on Oct 4, 2010 15:28:57 GMT 1
speakertoanimalsThe attractive force g felt by a satellite is porportional to the inverse square of the distance from the earth. So, the earth's gravitational field is a 3d map if you like, of the gravitational force exerted by the earth at any point in space. It is sometimes desctibed by the 2D analogy of a ball bearing on a rubber sheet. So, if you put two clocks in this gravitational field, they will measure the same time only when they are at places of equal gravitational potential ... or 'g'. If they are positioned at places with different local values of 'g', they will read differently. This is what the experiment showed, in your link.
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Post by eamonnshute on Oct 4, 2010 15:37:18 GMT 1
So, if you put two clocks in this gravitational field, they will measure the same time only when they are at places of equal gravitational potential ... or 'g'. If they are positioned at places with different local values of 'g', they will read differently. Gravitational potential is not the same as the acceleration due to gravity. Saturn's equatorial gravity is 1.065 g, but the time dilation on Saturn is much more than on Earth, because Saturn is more massive, so the gravitational potential is much greater, despite similar surface gravity.
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