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Author Topic: If the gravity constant G varies by 0.1%, will this effect the speed of light?  (Read 4477 times)

Offline acsinuk

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The attached physics.org article http://phys.org/news/2015-04-gravitational-constant-vary.html  indicates that even physical constants are inexact if the body measuring them is rotated at a different speed.
If our length of day changes; then our time changes. So radio active decay time changes but so will the speed of light but we can't measure it! or can we?
« Last Edit: 26/08/2015 09:25:18 by chris »


 

Offline Colin2B

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The attached physics.org article http://phys.org/news/2015-04-gravitational-constant-vary.html  indicates that even physical constants are inexact if the body measuring them is rotated at a different speed.
No, the article indicates a correlation, but not a cause. There is a suggestion that shifting core density affects the rotation rate, not the other way round.
If our length of day changes; then our time changes.
No, we no longer measure time using length of day.
So radio active decay time changes but so will the speed of light but we can't measure it! or can we?
Length of day cannot affect radioactive decay or speed of light.
A change of gravitational constant would affect relative speed of light, but the change would be the same throughout the gravity field so it shouldn't affect, say, the GPS system.

The effect mentioned is far, far less than the 0.1% you suggest.
 

Offline Bored chemist

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If G varied that much then a good pendulum clock would be all it took to show the effect.
they don't.
 

Offline acsinuk

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Sorry, Yes, article says percent fluctuation 10^-4 which is less.  However, Essens Caesium clock is claimed to be accurate to one second in 300 years and latest Caesium fountain at NPL one second in 158 million  years.
But if the speed of rotation of our planet or suns velocity to the magnetic centre of the galaxy is varying in time; then so are our atomic clocks
 

Offline Colin2B

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... if the speed of rotation of our planet or suns velocity to the magnetic centre of the galaxy is varying in time; then so are our atomic clocks
Could you please explain the mechanism by which this occurs, using standard physics.
 

Offline PmbPhy

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Quote from: acsinuk
The attached physics.org article http://phys.org/news/2015-04-gravitational-constant-vary.html  indicates that even physical constants are inexact if the body measuring them is rotated at a different speed.
It doesn't say that. It says that the value obtained in the measurement varies. It doesn't say that the value of G is inexact due to the rotation of the body. If current theory is correct then that'd be impossible because the value of G is independent of the particular body that one is taking measurements near. The article notes that it's probably a problem with the measurement process because it appears to correlate with the 5.9-year oscillatory period of Earth's rotation rate.

Quote from: acsinuk
If our length of day changes; then our time changes.
Not at all. Just because the length of the day changes it doesn't mean that "our time" changes. However I'm not 100% clear on what you mean by "our time." Can you please clarify that for me please? Thank you.

Quote from: acsinuk
So radio active decay time changes but so will the speed of light but we can't measure it! or can we?
Decay rates don't change nor will the speed of light. Don't forget that this same phenomena should also occur with the other planets but you shouldn't expect to get the same value if G because they all have separate seasons and rotation rates etc. The speed of light and decay rates are independent on the planet on which one measures them.
 

Offline acsinuk

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We really need the measurement of G taken at several different labs at separate locations at exactly the same time daily. Then we can properly assess the variations.
Looking at our rotation from the centre of the galaxy our relative velocity changes as we rotate the sun which must surely effect our absolute time frame reference and probably G as well 
 

Offline Colin2B

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....... our relative velocity changes as we rotate the sun which must surely effect our absolute time frame reference and probably G as well
It does not affect atomic decay which is our time reference and there is no obvious mechanism by which it would affect our G.
 

Offline jeffreyH

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G is a constant as is the speed of light and has to be in all inertial frames. Light has a coordinate speed. Should then G not have a coordinate value?
 

Offline PmbPhy

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G is a constant as is the speed of light and has to be in all inertial frames. Light has a coordinate speed. Should then G not have a coordinate value?
No. Light is a fundamental constant in nature and so is G.
 

Offline acsinuk

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Yes, c velocity of light and big G are both constants but what if the magnetic linkage to centre of our galaxy is varying.  With units of  MKS [m^3kg^-1 and Sec^-2] only; there is no suitable or sensible way of referencing tiny changes in the magnetic link?
 

Offline jeffreyH

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Yes, c velocity of light and big G are both constants but what if the magnetic linkage to centre of our galaxy is varying.  With units of  MKS [m^3kg^-1 and Sec^-2] only; there is no suitable or sensible way of referencing tiny changes in the magnetic link?

I don't see why you constantly link magnetism and gravity together. They are two distinct forces.
 

Offline acsinuk

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The reason is time dilation.  If it is a fact that G is varying then the common factor is time and this is relativistic.
So looking from the centre of galaxy the sun has a relativistic velocity and time setting our solar reference frame. But we are rotating the sun so our relativistic velocity and time when viewed from the magnetic centre of the galaxy will vary as is evident from the G readings.
 

Offline Colin2B

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The reason is time dilation.  If it is a fact that G is varying then the common factor is time and this is relativistic.
So looking from the centre of galaxy the sun has a relativistic velocity and time setting our solar reference frame. But we are rotating the sun so our relativistic velocity and time when viewed from the magnetic centre of the galaxy will vary as is evident from the G readings.
1. You are using the wrong reference frame
2. Magnetic doesn't affect it as has already been pointed out.
 

Offline mathew_orman

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In my personal opinion, since time is derived from periodic motion of our planetary system the new reference time unit would have new value. So speed of light will have a different value either larger or smaller...
 

Offline Colin2B

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In my personal opinion, since time is derived from periodic motion of our planetary system the new reference time unit would have new value. So speed of light will have a different value either larger or smaller...
The rotation of our planetary system was ok historically, but contains too many variations to be a modern standard. By 1950s there were so many adjustments that it was abandoned in favour of more stable standards eg atomic vibrations.
Anyway, there is no logic to assuming that if the earth slows down - which it is - that the speed of light will change, any more than assuming that if your watch slows down the speed of your car will change!
 

Offline mathew_orman

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There is logic: if one not using reference winch one would alter it will have no effect of speed of light...
But I thing the question and answer he is looking for is: is gravity affecting speed of light...
In my personal opinion gravity does not affect the propagation of light or any other type of electromagnetic waves...
 

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