# c

Discussion in 'Physics & Math' started by ajanta, Mar 29, 2017.

1. ### ajantaRegistered Senior Member

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611

The Postulates of Special Relativity. The laws of physics are the same in all inertial frames of reference. The speed of light in vacuum has the same value c in all inertial frames of reference.

"" The Postulates of Special Relativity. The laws of physics are the same in all inertial frames of reference. The speed of light in vacuum has the same value c in all inertial frames of reference.

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299 792 458 metres per second (approximately 3.00 × 10 8 m/s, approximately 186,282 mi/s); it is exact because the unit of length, the metre, is defined from this constant and the international standard for time.

According to special relativity, c is the maximum speed at which all matter and hence information in the universe can travel"".(From wiki)

We know that a clock at strong gravity ticks slower than a clock at weak gravity.

Now I had a concentration to c.
Suppose, PV cell of point B is at powerful gravity than the PV cell of point C. So when the clock of point B ticks 1/2 second then the clock of point C (At weak gravity) ticks 1 second.
Here I'm explaining about a trap....
So simply when the clock of point C will tick 1 second then photon of point A will certainly reach at the point B(Because the distance between the point A and B is 3.00 × 10 ^8 m), but then the clock of point B ticks 1/2 second(when the clock of point C will tick 1 second

) ...

Now my question is...why the PV cell of point B can receive photon of point A as TACHYON in 1/2 second ? Because the distance between A and B is 3.00 × 10^8 m and photon can travel the distance in 1 second only, but not in less than it.

So, Is the postulates of special theory of relativity going against its own ???

3. ### originIn a democracy you deserve the leaders you elect.Valued Senior Member

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A person at clock B would see the light takes 1 seccond to go the 3 x 10^8 m by their clock. A person at clock B would see the light takes 1 second to travel 3 x 10^8 m by their clock. The person obseverving from a distance would see light travel 3 x 10^8m in 1 sec by their clock.

SR wins again.

Last edited: Mar 29, 2017

5. ### The GodValued Senior Member

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But SR does not say that c will be same in different gravity zones.

7. ### ajantaRegistered Senior Member

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611
sorry.. Sorry..

Then the time duration at B point is certainly 1/2 second. Because then the clock of point C ticks 1 second and photon travels from point A to B in this time duration.

8. ### ajantaRegistered Senior Member

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611
If it is, then the clock on point C would tick 2 second and how photon travels 3 x 10^8 m in 2 seconds ? Is the time duration of point C is wrong ?

Last edited: Mar 30, 2017
9. ### ajantaRegistered Senior Member

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611
But I don't think the variable speed of photon rather than another kind of something.

10. ### originIn a democracy you deserve the leaders you elect.Valued Senior Member

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Ok, I live in the US where there no longer is any objective reality so your idea is as good as any other.

11. ### DaveC426913Valued Senior Member

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Are you taking into account distance contraction along the direction of the gravity well?

The distances will not be measured to be 3.00 × 10^8 m in all observations. They will be observed to be shorter than that.

For example, the distance between B and A will be observed to be only 1.50 × 10^8 m. And a photon would be correctly observed to traverse that distance in 0.5s.

12. ### Q-reeusValued Senior Member

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It's trivially true the proper speed of light in vacuo is fixed at c. It's equally true the coordinate speed of light in vacuo is a function of gravitational potential - and, in say standard Schwarzschild coordinates, additionally a function of direction. A lot of folks get hung up by insisting there is one and only one correct pov/definition.

13. ### ajantaRegistered Senior Member

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611
Actually sir, I'm thinking about another trap in about vacuum. I will post later, thanks.

14. ### ajantaRegistered Senior Member

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611
If the 0.5s is of clock at B point then the time duration of the clock at C point is 1s so how the observer of point C will measure the distance 1.50 × 10^8 m (A between B) in 1s ?

15. ### ajantaRegistered Senior Member

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611
what will be your explanation when gravitational force will
be tiny(ignored) and difference of time duration is enough between B and C point ?

16. ### Michael 345Home 2 days still jet lag sleepyValued Senior Member

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I sort of understand your reasoning and the problem you are seeing

I am short on truly offering a full explanation

But as I understand you are saying

clock B is in strong gravity and

clock C in weak gravity correct?

I would ask what is the gravity at point A?

Is it the same as clock B strong?

Also (sorry I'm not being picky here) gravity would not make an abrupt change from strong to weak over distance (I guess it can within a thought experiment)

Gravity varies with the square root of distance fading away the further away from mass

That being said I hope someone can give you a answer as I am very interested also

I suspect the explanation will lay in distance contraction but again I am far from able to decently explain it to you

17. ### ajantaRegistered Senior Member

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611
Thanks Michael ! Gravity of A
Point is neglected.
Sir, I'm not well educated but directly I'm gonna explain that I understand.

Suppose observer B is drunk a little bit and he observed the earth as little bit flat and observer C is drunk well so he observed the earth as enough flat. Both B and C observers affected by alcohol. So if the earth is "really" as sphere then it doesn't make sense about the different result of from B And C and if there are no observer then it does not make sense that earth will change into flat type.

So if the distance between A and B is "really" contracted(when light speed is constant) then the photon travels (3.00 × 10 ^8) /2 m when the time duration of point B is 0.5s but then(same moment) the time duration of C point is 1s so, Is there no distance (A to B)contraction(Because in 1s photon will travel 3.00 × 10 ^8 m) ? How can it possible ??

18. ### DaveC426913Valued Senior Member

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??
This is the default state.
If the gravitational gradient is small, then the distance between B and A will be 3×10^8m, and photons will take one second to traverse it.
Where's the problem?

(Perhaps I am misinterpreting your diagram.)
Where is the mass? At A? B? or at C?

19. ### Michael 345Home 2 days still jet lag sleepyValued Senior Member

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I did some looking up to try and increase my understanding of the idea you are putting forward

I am sure that I am not the best at giving you a definitive answer

It appears that the answer lies in time dilation

Not distance contraction

I take this to mean in the strong gravity

from A to B the time dilates to 1 second

In the weak gravity

from B to C it is 1 second

I am sure there more qualified persons out there with better explanations

This is a late post as it was written about 4 hours ago and due to doggy hotel WiFi didn't get sent

At 4am no one on line so here's hoping

ajanta likes this.
20. ### DaveC426913Valued Senior Member

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OK, hang on. Part of the problem here may be that you appear to be speaking about absolutes. B cannot "know" at what rate clock C is ticking at without making an observation.
You can only talk about what each observes happening at remote points. You cannot talk about what is happening unless you are at that location.

So, what you need to do is reframe the scenario to describe what each observer, A, B and C sees.
You should also label the mass's location.
And you can drop the 'PV cell'; we can take for granted that we can sense a photon.

21. ### ajantaRegistered Senior Member

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611
Yes Michael ! At the same moment distance(A to B) is not shorter/longer than the distance (A to B) but it can be true( scientific evidence for B and C when they observe) when something/someone is chaining space-time to show it to B and C observers separately

In my trap time dilation doesn't make sense instead of real distance contraction. (when speed of light is not variable)

22. ### Michael 345Home 2 days still jet lag sleepyValued Senior Member

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I am way outside my bubble of comfort with even my explanation

I will wait with you for someone to provide a definitive answer and hope my brain can understand

23. ### rpennerFully WiredValued Senior Member

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You two have both made the same mistake of using 1905 Special Relativity which deals with places where no force on an object means it moves with constant velocity but talking about situations were objects don't move with constant velocity because of gravity, so best dealt with in the framework of 1916 General Relativity.

Because in General Relativity, which deals with gravity, the local speed of light in a vacuum is always c, but since B is in strong gravity and C is not, it follows that most of the path light takes between B and C is not local to either.

So you have to use calculus and the description of space-time between B and C to calculated how long the light's trip takes in B's coordinates and in C's coordinates.
Likewise you can't just assume that B's rulers and C's rulers will agree on the distance between B and C.

We really do have an actual situation like this, because GPS satellites orbit the earth quickly very high, so GR is needed to correct for relative speed and differences in gravity so that clock rates can by synchronized very precisely between ground and orbit and light-speed signals are sent back and forth. The key to synchronizing real moving clocks is to use the best physics (General Relativity) and use that to model one coordinate system ( an idealized model where sea level on Earth is all at the same time ) and to tune clocks which aren't stationary relative to the Earth's surface or not at sea level to tick at the coordinate time rate, not the local rate of the SI definition of second.

Because c is much faster than GPS satellites and because the Earth's radius is much more than 1 cm, these changes are only noticed by precision engineering designed to perpetuate the Earth-based standards of distance and time. But those standards, as all coordinate systems are in General Relativity, are arbitrary human choices not relevant to the physics of the universe.