The Naked Scientists

The Naked Scientists Forum

Author Topic: Is the speed of light the same to all observers?  (Read 12334 times)

Johann Mahne

  • Guest
Is the speed of light the same to all observers?
« on: 23/05/2011 17:01:02 »
Johann Mahne  asked the Naked Scientists:
   
Hi Chris,

If the "metric expansion" of space exeeds the speed of light itself, then does the statement "The speed of light is the same to all observers" still hold true?

What do you think?
« Last Edit: 23/05/2011 17:01:02 by _system »


 

Offline Phractality

  • Hero Member
  • *****
  • Posts: 523
  • Thanked: 1 times
    • View Profile
Is the speed of light the same to all observers?
« Reply #1 on: 23/05/2011 20:27:23 »
Most cosmologists think in terms of "comoving coordinates", in which the increasing distance of distant galaxies is not considered to be a "velocity". Velocity is measured relative to the coordinates, and the coordinate, themselves, are expanding.

The coordinates are like a grid of measuring chains, with new chain links being added all the time. For every 4 x 10^17 links, one new link is added every second. Observers who are comoving with eachother are stationary relative to the chain links near them. Light has the same speed everywhere relative to the chain links, so all observers perceive light moving at the same speed.

You could define a different kind of coordinate system, consisting of a grid of ideal, massless, unstretchable chain links, with no new links being added. In such a coordinates system, only one point (the origin) would be stationary relative to a set of comoving objects. Links far from the origin would be accelerating relative to comoving space; if they had mass, they would pull away from the origin. The expansion of space, in such a system, would be equivalent to a gravity hill centered on the origin, wherever the origin happens to be. The speed of light would still be the same everywhere by definition. But an observer stationary relative to the coordinates would see comoving meter sticks near him length contracted, while a comoving observer would see the chain links near him lenght contracted. Each observer would see light moving faster in terms of the other observer's meter sticks, but at the same constant speed in terms of his own meter sticks.
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
Is the speed of light the same to all observers?
« Reply #2 on: 24/05/2011 08:19:15 »
Yes.

In simple terms, speed is distance divided by time.  Both distance and time (the 'length' of a meter and a second) are variable and they vary in such manner that the speed of light always remains constant.
 

Offline simplified

  • Sr. Member
  • ****
  • Posts: 428
    • View Profile
Is the speed of light the same to all observers?
« Reply #3 on: 24/05/2011 14:41:58 »
waitedavid137   Posted: May 6 2011, 06:14 AM
Report this post · Quote


Member


Group: Power Member
Posts: 106
Joined: 17-June 10

Positive Feedback: 100%
Feedback Score: 5
View/Add Feedback New
Warn: (0%) 

QUOTE (dimazin @ May 5 2011, 07:12 PM)
What is "slowing of light"? Is it slowing of light speed in your understanding?

It means that with respect to the coordinates appropriate for an observer far from any gravitational sources the speed of light near a mass like a star for example as calculated by those coordinates is less than c."
         see link: http://www.physforum.com/index.php?showtopic=29063&st=15
         
« Last Edit: 01/06/2011 19:12:10 by simplified »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #4 on: 25/05/2011 09:07:07 »
Johan, you are asking one of the most important questions I know. Why is the speed of light a constant. When I see people answer this question using relativity 'proving' that it has to be a constant exemplifying it by 'frames of reference' counting on the differences, I see people that stared themselves blind on their professors explanations. The truth is both simpler, and more confusing. When Einstein created the theory of relativity he built it on Maxwell's electromagnetism, well not really, he really built it on his imagination, but he anchored it in Maxwell.

What I think he did was to look at light, and the experiments we already had, and from that draw one simple conclusion. That light to its nature is invariant, of one same 'speed', no matter if its source was moving or standing 'still', as relative some arbitrary point. And furthermore the same would be true for the 'sink' (eye). Motion had nothing to do with that 'relative constant speed'. From that simple conclusion you will get 'time dilations' and 'Lorentz contractions' when you start to introduce 'frames of reference'. And I think that he must have used the experiments proving that light didn't care for earths relative motion to prove it to himself.

It's a question that cuts to the marrow of physics, which hasn't been answered by any 'theory' yet. We know that light is a constant, we can see that the room it 'propagates' in deforms and distorts depending on observer. We know that there are no exact same 'frames of reference', even though people labor under the apprehension that we can use such definitions, rigidly speaking they just don't exist. Einstein left us a fantastic beautiful build, but it's time to look at the structure I think, and try to answer the real question.

Why is light always a constant 'c'.
It's worth thinking of.
« Last Edit: 25/05/2011 09:14:22 by yor_on »
 

Offline simplified

  • Sr. Member
  • ****
  • Posts: 428
    • View Profile
Is the speed of light the same to all observers?
« Reply #5 on: 25/05/2011 10:22:29 »
Speed of light is a constant to local observer.Speed of light is not a constant to external observer. :(
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #6 on: 25/05/2011 18:38:32 »
Simplified, that doesn't make sense to me?
Where do you get that notion from?
 

Offline simplified

  • Sr. Member
  • ****
  • Posts: 428
    • View Profile
Is the speed of light the same to all observers?
« Reply #7 on: 25/05/2011 19:49:56 »
Simplified, that doesn't make sense to me?
Where do you get that notion from?
The gravitational delay of light speaks about my concept. And you should understand  that far gravitation does not reduce my coordinates,but slows motion of that local light! [8D]
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #8 on: 26/05/2011 11:27:21 »
There is a distorted room time in a gravitational field that makes my head hurt if that is what you was thinking of? And as seen from outside that gravity you see one thing (spacecraft hanging at EV) and inside it you see something else (space 'growing') but none of the observer will see light getting a new 'speed', neither when they measure their own frame of reference, or as they measure the 'opposite' frame of reference.

The light always come at you at 'c'. If it didn't you could assume that light coming from a black holes EV should be 'slower' but it isn't. And that we should see on Earth measuring the incoming light from the rest of the universe. Only if you accept that light nowhere has a different speed will Einstein make sense to you :)

The physics we have make some assumptions.

Space is homogeneous and isotropic, meaning that it looks and behaves the same everywhere, also defining that Space is expected to give us the same 'physics outcomes' everywhere. SpaceTime is also expected to be symmetric under a time translation, meaning that the experiment you do today will be valid tomorrow, as well as having been valid yesterday. We also assume that the equations of physics still will work under a motion. All of those are reasonable ideas. If you succeed to prove it otherwise you would introduce a 'magic universe' where physics would differ depending on your position in some coordinate system relative some other point. That's also why light is expected to be a constant, having a unvarying speed in a vacuum.

the other way becomes the magical kingdom, where different areas is presumed to have different lightspeeds, also invalidating the fact that three observers uniformly moving can observe the same point in space, seeing three 'time dilations' there. In Einsteins universe this is possible, in a universe where all points is expected to be regulated by some 'magical lock down' aka, for example gravity, that shouldn't be possible.
 

Offline simplified

  • Sr. Member
  • ****
  • Posts: 428
    • View Profile
Is the speed of light the same to all observers?
« Reply #9 on: 26/05/2011 16:23:32 »

The light always come at you at 'c'. If it didn't you could assume that light coming from a black holes EV should be 'slower' but it isn't. And that we should see on Earth measuring the incoming light from the rest of the universe. Only if you accept that light nowhere has a different speed will Einstein make sense to you :)



[/quote] :DEven traveling light from Sun has delay about 53 microseconds!
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
Is the speed of light the same to all observers?
« Reply #10 on: 26/05/2011 17:54:19 »


Why is light always a constant 'c'.
It's worth thinking of.

Why does light have a very fast but finite speed?  We know that a gravity well does affect light.  If ‘time were a constant’ then it would slow the speed of light down but as time is variable, the speed of light remains constant and time dilates.

Everywhere within the universe there is a ‘gravitational field’ therefore time is being dilated everywhere.  In other words the local time dilation is due to the strength of gravity in that locale. Hypothetically, if you remove the gravitational field then a photon can travel at it’s natural speed which is instantaneous. 

I could elaborate on this but then it would be new physics.

See Time 1 http://www.thenakedscientists.com/forum/index.php?topic=39214.0;topicseen
Time 2 http://www.thenakedscientists.com/forum/index.php?topic=39218.0
Gravity and time http://www.thenakedscientists.com/forum/index.php?topic=39216.0
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
Is the speed of light the same to all observers?
« Reply #11 on: 26/05/2011 18:27:26 »
Mike - the way gravitational time dilation is calculated at present is that in a region with a low graviational potential time will pass more slowly - we measure this as a ratio of coordinate time (there are differences between this and gravitational field strength which you are relying upon).  Coordinate time is the measured time between events for a higher ticking clock observer at an arbitrarily high graviatational potential ie an arbitrarily large distance.  By definition light travels at c in this arbitrarily high-ticking region. 

To postulate a background gravitational potential that is everywhere, needs more theory, testability, and reason than an extrapolation of gravitational time dilation. The reason you need to do more than extrapolate is that time dilation due to gravitational potential goes to a limit of coordinate time and arbitrarily high gravitational potential but not infinite speed of light. 
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #12 on: 26/05/2011 19:56:41 »
What are you quoting simplistic? Feel free to give me the link to what you mean there
Are you thinking of group and phase velocity, or is it something else you mean?

For you locally measuring the speed of light it will always be at 'c'. There are some tricks in where you by using clocks in a accelerating frame can define light as having different speeds depending on direction, but those are created by ignoring the way the space distorts and gravitates under a acceleration. And even there when measuring the lightspeed directly you will find it to be at 'c' as I understands it. So, ignoring conceptual frames of reference, going for what you actually measure firsthandedly there will be no measurement giving you any other speed than 'c'. That all speeds as such are arbitrarily defined doesn't change this. It is a constant.
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
Is the speed of light the same to all observers?
« Reply #13 on: 27/05/2011 08:03:03 »
Mike - the way gravitational time dilation is calculated at present is that in a region with a low graviational potential time will pass more slowly - we measure this as a ratio of coordinate time (there are differences between this and gravitational field strength which you are relying upon)Coordinate time is the measured time between events for a higher ticking clock observer at an arbitrarily high graviatational potential ie an arbitrarily large distance.  By definition light travels at c in this arbitrarily high-ticking region. 

To postulate a background gravitational potential that is everywhere, needs more theory, testability, and reason than an extrapolation of gravitational time dilation. The reason you need to do more than extrapolate is that time dilation due to gravitational potential goes to a limit of coordinate time and arbitrarily high gravitational potential but not infinite speed of light. 

Surely, it must follow if gravity from a massive object dilates time in its locality then the average background gravity within the universe must have an effect upon time.  This must be self evident.

This is just the average background gravity of the universe (far from a source of gravity).

The universe could be defined as a gravitationally bound system that contains the aggregate of all existing matter, energy, and space. I am not postulating anything new here the universe does have a background gravitational 'field' (for lack of a better word).  

I don't know as I understand this sentence correctly.  It may be that you are using 'dilation' in a confusing manner where 'contraction' would be more appropriate?  Ultimate time dilation is found at the event horizon of a black hole. And yes, this is a limit to coordinate time.  If this black hole was 'the black hole at the end of the universe' then time and space would have been 'squeezed' out of existence.  I don't see any of this as being 'new physics' and therefore, does not need more theory and testability.

That the universe has a background gravitational 'field' is self evident.
Gravitational time dilation has been experimentally proven.
Therefore it must follow (my quote)
"Everywhere within the universe there is a ‘gravitational field’ therefore time is being dilated everywhere.  In other words the local time dilation is due to the strength of gravity in that locale".
The only extrapolation that I have made is to add (my quote)
"Hypothetically, if you remove the gravitational field then a photon can travel at it’s natural speed which is instantaneous".
It must follow that if gravity dilates time then the lack of gravity must contract time.  The ultimate contraction of time being infinite contraction.  If that is so then it follows that the speed of light would in a 'sense' be infinite but still obeying the idea that the speed of light is constant.
I must just add this as it puts the above into context.  For a photon to travel instantaneous it would have to be outside of a gravitational 'field' which means outside the universe but that would also put it outside of time itself.

Can it be experimentally proven that a photon travels instantaneously outside of a gravitational field?  Probably not as we can not divorce the experiment from the all encompassing effects of gravity.
However, the opposite experiment can and has been done and proved that gravity does dilate time.
Is this not essentially the same experiment?
It is generally accepted (but not proven) that time stands still at the event horizon of a black hole.
It takes no more stretch of the imagination to accept that in a gravity free environment a photon travels instantaneous.
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
Is the speed of light the same to all observers?
« Reply #14 on: 27/05/2011 08:35:46 »
Quote from my last post
Can it be experimentally proven that a photon travels instantaneously outside of a gravitational field?  Probably not as we can not divorce the experiment from the all encompassing effects of gravity.

This does however, fit in with quantum mechanics idea of energy of the vacuum.

If energy can spontaneously appear from the vacuum it is doing so outside of time.  In which case it must be instantaneous.  Therefore, it follows that outside of a gravitational field a photon travels instantaneous.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #15 on: 27/05/2011 11:38:51 »
Mike, your ideas are not mainstream. Neither are they backed up by any evidence. Place them in New Theories, not here.
 

Offline JP

  • Neilep Level Member
  • ******
  • Posts: 3366
  • Thanked: 2 times
    • View Profile
Is the speed of light the same to all observers?
« Reply #16 on: 27/05/2011 12:52:23 »
This does however, fit in with quantum mechanics idea of energy of the vacuum.

If energy can spontaneously appear from the vacuum it is doing so outside of time.  In which case it must be instantaneous.  Therefore, it follows that outside of a gravitational field a photon travels instantaneous.

This does not fit with quantum mechanics or any other mainstream theory.  If it's your own theory, please state it as such and don't mislead people into thinking it's mainstream.  If it's your own theory, please keep it to the New Theories section, as yor_on suggested.
 

Offline MikeS

  • Neilep Level Member
  • ******
  • Posts: 1044
  • The Devils Advocate
    • View Profile
Is the speed of light the same to all observers?
« Reply #17 on: 29/05/2011 08:56:37 »
I have taken your advice and opened this in under new theories.  'What is the speed of light outside of a gravitational field?'
 

Offline Ken Hughes

  • Full Member
  • ***
  • Posts: 56
    • View Profile
Is the speed of light the same to all observers?
« Reply #18 on: 29/05/2011 15:17:50 »
Johann,

My understanding of "The metric expansion of space" is of an abstract mathematical phenomena and not necessarily of a real event. Certainly there is no velocity involved since all velocity in our universe is measured against space itself, or at least some reference frame within space or space-time. Space, may or may not "expand", although I don't see how "expansion" is an appropriate word or idea within our universe.
I guess this has been answered differently and more traditionally with the co moving reference frame argument.

What I wanted to ask was a basic question about relativity connected to this thread.
Is the "expansion" of space derived from GR or simply implied from our redshift observations and, do we believe it is a real effect or just an abstract mathematical tool which gives us the right answers when using relativity theory?
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #19 on: 30/05/2011 00:14:33 »
No Ken, relative motion is always defined relative objects moving, not relative space. Although it will be the 'space' metrics that change, when defining those objects moving relative each other. And the metric expansion of space is related to the way all those objects seems to be accelerating from everyone else, as confirmed through the red shift and brightness of distant supernovae. But it could be wrong of course, there might be some other explanation that we haven't realized yet. Still, it's no weirder than we existing at all :)
 

Offline Ken Hughes

  • Full Member
  • ***
  • Posts: 56
    • View Profile
Is the speed of light the same to all observers?
« Reply #20 on: 30/05/2011 09:09:51 »
Thankyou Yor_on,

Yes, I understand we normally deal with relative motion by considering motion between two bodies, then translate the effects by defining the metrics.
But, do we really have to do this?

Non mainstream questioning from now on
If a ship is passing through a gravitational field, why can we not consider the motion relative to some particular reference frame within the field? Perhaps you might argue that the field in question is directly related to the body producing it, but is the field any less real than the (planet)?
Would it not be possible to develop relativity based on relative motion between reference frames or is this already implicit within the theory?

I don't want to re create the Aether, but surely there are frames of reference within space-time that we could use as datums?


Regarding observed redshift, if we consider the possibility that time itself might be passing more rapidly now than in the past, then this could not only give us the same redshift observations, but it would do so without the necessity for an expanding space. Occams Razor would prefer this option and I certainly do as I have a problem accepting the expansion of nothing.
There is no scientific justification for assuming that time has always passed at the same relative rate throughout the eons. If we extrapolate in the same way as we have done to deduce expansion, then we get the slowing down of time to a standstill at the beginning. No Big Bang, just a Slow Temporal Eruption (STE).

« Last Edit: 30/05/2011 09:21:02 by Ken Hughes »
 

Offline imatfaal

  • Neilep Level Member
  • ******
  • Posts: 2787
  • rouge moderator
    • View Profile
Is the speed of light the same to all observers?
« Reply #21 on: 30/05/2011 09:29:05 »
Ken would you mind if I moved the above post to New Theories? - as you acknowledged it really has moved away from the OP and from mainstream knowledge.
 

Offline Ken Hughes

  • Full Member
  • ***
  • Posts: 56
    • View Profile
Is the speed of light the same to all observers?
« Reply #22 on: 30/05/2011 09:57:36 »
That's fine thanks, but I was asking for a mainstream response to the non mainstrean idea.
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Is the speed of light the same to all observers?
« Reply #23 on: 30/05/2011 14:17:04 »
There are several difficulties, some of them directly related to how we define motion from a relativistic perspective. But the uppermost is that space is what you find everywhere. Without space nothing can exist, it's in your cup of coffee, it's in your molecules, it's whats make up 99 ~ of a atom. And there are no distinguishing signs to space. It's the same in outer space as in that atom. If we found a way to distinguish one point of space from another we would have a new theory.

And you can't use gravity as that is a dynamic phenomena, coupled to energy, invariant mass and motion. Actually space confuses me, if I would define from a QM perspective I could mumble something about 'zero energy' and a sea of 'virtual particles' but that is nothing we can measure. That's a theory explaining some really strange properties at a minuscule plane, not anything we can hold up and say. "This is a virtual particle".

Space is without friction, Space is empty, there is none proven it to be otherwise macroscopically yet. And being so there is nowhere space will differ from any other point of space. You could assume, as I do, that 'space' is 'gravity'. To me 'space' has two qualities, it has a distance and it contain 'gravity' even when unmeasurable.
==

Gravity is in fact a 'resistance' of sorts, and what any object will do when moving in a space is to adapt to least energy expended, meaning that it will follow a geodesic (free fall/ weightless). As the universe prefers it that way you could say that for a universe in equilibrium all motion will be 'uniform' .

Electro magnetic energy is 'everywhere' if you like. But it does not leave itself to be observed in the same manner as macroscopic objects. A football will be observed as it comes, a photon will only be observed as it annihilates/interacts. That leaves you two ways to define EM. From a point of 'propagating' or just from a point of 'interacting'. Most theories today treat it as 'propagating' and so we find ourselves in a quagmire of definitions when it comes to its duality waves/particles containing a plethora of extremely confusing and clever theories. If you define EM as it actually is then it is 'everywhere' but there is 'nothing' propagating as such, instead you have something directly coupled to 'times arrow' that will present you with a effect that you directly can translate into 'propagation'.

A football is in some ways also a bundle of 'photons' as it is those that will define the football to your eyes, as it moves in the air. But invariant mass and energy/photons is not the absolute same, and that you prove each time you lift your cup looking down at the 'light' dancing on its surfaces.
« Last Edit: 30/05/2011 14:31:06 by yor_on »
 

Offline Ken Hughes

  • Full Member
  • ***
  • Posts: 56
    • View Profile
Is the speed of light the same to all observers?
« Reply #24 on: 30/05/2011 14:29:26 »
Hi Yor_on,

It seems we completely agree on space being totally............. NOTHING!

That's great because it is the first assumption in my new theory which I cannot discuss here. (Yeah, I know, everyone's got a theory, but one may be true!)(Yeah, I know everyone thinks their theory is true, but that still doesn't mean that one (or more) of them can't be)

I do not agree with you that gravity is the only thing in space, although we very nearly do agree.

It is TIME that is the only reality in space, not gravity, but then, since Newtonian gravitation can be regarded as the curvature of time,(this is mainstream), I think it could be said that we agree on this also.

Oh, and by the way, we do have a way of distinguishing one point in space from another and that is by comparing the passage of time between each frame. (ie, the time rate in one frame of reference compared to the time rate in another. Mainstream scince agrees they are different)

In other words, space-time is the time rate field within the void.

I don't think I've strayed from the mainstream.

Oh, and another thing, space cannot exist on its own, not without the passage of time. Therefore we have our space-time continuum.
« Last Edit: 30/05/2011 14:37:20 by Ken Hughes »
 

The Naked Scientists Forum

Is the speed of light the same to all observers?
« Reply #24 on: 30/05/2011 14:29:26 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums