The Speed of Light is Not Constant

[paddoboy]

“When forced to summarize the general theory of relativity in one sentence: Time and Space and Graviton have no separate existence from matter.”
―Albert Einstein

Doesn't that support the concept of the reality of time and space?
I mean we certainly know matter is real.


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Experiments continue to show that there is no 'space' that stands apart from space-time itself...no arena in which matter, energy and gravity operate which is not affected by matter, energy and gravity. General relativity tells us that what we call space is just another feature of the gravitational field of the universe, so space and space-time can and do not exist apart from the matter and energy that creates the gravitational field. This is not speculation, but sound observation."
Sten Odenwald:
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[forrest noble]

Doesn't that support the concept of the reality of time and space?
I mean we certainly know matter is real.

Concepts and perspectives are not reality themselves as philosophers explain, but they are the basis of what science is comprised of. I consider time an interval of change, but it takes an intelligence of some kind to consider this concept. I think space was rightly explained by Spinoza as being an extension of matter. My preferred definition of space is the distance between matter and the volume which it encompasses, and nothing more. By this definition space does not exist outside the confines of matter, so like time it is also defined by the existence of matter, and not something separate from it. Of course many also would disagree with this definition since there are many different definitions and understandings of what space is also. I would agree that space can be perceived or considered as a separate entity from matter, but I think the connection between them should not be severed to enable the best understanding of space, as in Einstein's quote.

 

[Write4U]

Write4U

That is simply wrong, the curved path means it takes the photon more time to cover that same coordinate distance. The coordinate distance is that between the hole and the wall in a straight line, the curved spacetime is longer(because it is curved)but the photon must cover the additional distance at exactly the same speed, it takes more time to travel a longer distance at the same speed and this is illustrative of time's dilation in an accelerating frame. The observer moving with the clock sees the photon at the same speed because his time is dilated too. But any outside observer will see the photon, traveling all the while at c, follow a bent path in a longer time than the coordinate distance would lead you to expect. That is time dilation and spacetime curvature. Photons never exceed lightspeed and bent paths are longer and mass causes spacetime to bend thus light takes longer to go the coordinate distance in a gravity field. It's coordinate speed is slower, it's actual speed through spacetime remains c.

Sorry, I still disagree. To an outside observer the light shines in a straight line (from the hole to the opposite wall), it's the box that is moving without affecting the light source (which is also located outside the box), but to the observer inside the box the movement of the box creates an illusion of curvature to the observer inside the box. But if the box is 386,000 miles across it takes the photon 1 second to cross that distance, regardless if the box is moving or not. As long as that distance between the two walls is maintained, it will take the light 1 second to cross the room and hit the other wall (in a vacuum).

Part of your misunderstanding is the position of the observer. In frame no difference would be seen, from a stationary frame the comoving observer's time is seen to go slower(dilated), light follows a bent path and it takes longer to "tick". Frame of reference causes lots of confusion in Realativity, but it is critical to understanding. You need to designate all of your statements with the frame of reference of the observer you are talking about.
Grumpy

I am afraid we are talking past each other, although I am trying to answer your "frame of reference". To the observer inside, the curved or diagonal line "appears longer", but the light ALWAY ARRIVES AT THE OPPOSITE WALL at the same time regardless of the speed of the box.

And that is my point, when measuring light (which always travels @"c", in a straight line). If the line is not straight it is never due to the photon, it is always the external environment which gives an appearance of changing behavior.

A photon always moves @ "c" and in a straight line . This is not controversial (?) No matter what happens to a photon it always behaves the same way. It is the conditions that change the apparent results (such as introducing an observer) never the photon. It IS the constant "c".

 

[brucep]

Hey bruce. Yeah it does get monotonous. I would say that they are experiencing the delusions of Russell Crowe's character in A Beautiful Mind, only without the "beautiful". Homely maybe, sometimes dog-ugly. But definitely twisted. Am I right? Are they simply not capable of understanding what a reference frame is? I keep thinking I've diagnosed the syndrome. At least that's my guess today.

It's the source of all the confusion. For the cranks it's a complete 'lack of will' to understand. Understanding would 'shoot a hole' into the delusion. A perfect example would be the recent threads where RJBerry and Farsight conclude the Schwarzschild coordinates are preferred.
Then tell us they understand the theoretical model enough to change it in the way RJBerry proposed. LOL. The 'logic escapes them' permanently. Irrevocably.

 

[Grumpy]

forrest noble

From my own opinion and related hypothesis time is a man-made concept. It is not part of the universe. It is simply a definition, understanding, hypothesis, etc. of intelligent beings.

So you think that time did not exist before there was a consciousness to perceive it? Time is certainly part of the Universe. As spacetime. The theory didn't come first, the study of how our Universe behaves came first. And what was observed dictated the structure of the theory. Einstein had two postulates, one of them was an observed fact, the other is an explanation of why that fact is a fact. The fact was that after hundreds of years of study it was determined that light is always measured to travel at exactly c in a vacuum with no variance due to the direction of travel or motion of source or observer. Relativity(the other postulate)is where the real genius of Einstein was applied to that fact, working out the ramifications of it being a constant, mathematically and conceptually. And every prediction of those ramifications, one of which is spacetime, have proven to be true except for gravity waves, and we already have indirect evidence of that last prediction. The Universe does seem to be real and Relativity is an excruciatingly precise map of it. So, time is a real dimension, you can see it in any good telescope, the further out you look, the further back in time what you are seeing is/was. And after looking at things more than about 8 million lys away it all happened before we even existed. So, no, time is not a human invention, it is a real feature of the Universe. You are confusing the map for the territory it describes.

Concepts and perspectives are not reality themselves as philosophers explain, but they are the basis of what science is comprised of. I consider time an interval of change, but it takes an intelligence of some kind to consider this concept. I think space was rightly explained by Spinoza as being an extension of matter. My preferred definition of space is the distance between matter and the volume which it encompasses, and nothing more. By this definition space does not exist outside the confines of matter, so like time it is also defined by the existence of matter, and not something separate from it. Of course many also would disagree with this definition since there are many different definitions and understandings of what space is also. I would agree that space can be perceived or considered as a separate entity from matter, but the connection between them cannot be severed, as in Einstein's quote.

Now you are confusing the glass for the water it contains. Spacetime is a framework, a field(Einstein called it the 4D spacetime manifold), a stage upon which the play of energy, matter and gravity occurs. The Universe would still be the Universe if there were no matter or energy, a dull Universe, but matter is only a very minor contaminate in our Universe, it's mostly yawning gulfs of empty space. Our nearest neighbor is more than four light years away(it takes light eight minutes to reach Earth from the Sun)and we live in an extremely crowded neighborhood compared to the spaces between galaxies. Yes, there is a connection, mass tells spacetime how to bend and spacetime tells matter how to move. Mass causes time to dilate, as does movement. The connection cannot be severed, it's all relative and it's all part of the same system, so is time.

Grumpy

 

[forrest noble]

Grumpy,

Lots of good content to your posting. Below are the few things that I differ concerning my views from yours.

"So you think that time did not exist before there was a consciousness to perceive it?"

The same things were going on before their perception, there was just no intelligence to conceive of time or give a name to it. What I believe is that a change of some kind must occur for the passage of time to proceed -- not that it ever could stop -- but local time can slow down under certain conditions.

".... The Universe would still be the Universe if there were no matter or energy, a dull Universe, but matter is only a very minor contaminate in our Universe."

Of course your statement is just a matter of different possibilities of theory. In my view there is, and only ever could be just one universe: the one we live in -- with no reason to expect variations of it, or that it could have developed otherwise. Again there are many different views, hypothesis, theories, on this.

".....Mass causes time to dilate, as does movement."

The influence of gravity causes time to dilate within matter, as does the motion of matter relative to the center of gravity in its location.

 

[paddoboy]

Concepts and perspectives are not reality themselves as philosophers explain, but they are the basis of what science is comprised of..

Sometimes "concepts" can in time be thought of as realities. I see this the case with space/time.
I still see the Einstein quote as supporting the reality space/time, if they have no separate existence from matter.

 

[brucep]

Sorry, I still disagree. To an outside observer the light shines in a straight line (from the hole to the opposite wall), it's the box that is moving without affecting the light source (which is also located outside the box), but to the observer inside the box the movement of the box creates an illusion of curvature to the observer inside the box. But if the box is 386,000 miles across it takes the photon 1 second to cross that distance, regardless if the box is moving or not. As long as that distance between the two walls is maintained, it will take the light 1 second to cross the room and hit the other wall (in a vacuum).



I am afraid we are talking past each other, although I am trying to answer your "frame of reference". To the observer inside, the curved or diagonal line "appears longer", but the light ALWAY ARRIVES AT THE OPPOSITE WALL at the same time regardless of the speed of the box.

And that is my point, when measuring light (which always travels @"c", in a straight line). If the line is not straight it is never due to the photon, it is always the external environment which gives an appearance of changing behavior.

A photon always moves @ "c" and in a straight line . This is not controversial (?) No matter what happens to a photon it always behaves the same way. It is the conditions that change the apparent results (such as introducing an observer) never the photon. It IS the constant "c".

You might think about what Grumpy is saying. In local frames of reference the speed of light is an invariant c and travels in a straight line [since local coordinates are 'everywhere in the universe' light always travels in a straight line]. That's the natural path of light over flat spacetime. We can evaluate this path with the Minkowski metric [the metric of flat spacetime]. If we choose to evaluate a 'spacetime event' from remote coordinates the evaluation depends on those specific coordinates and the evaluation can change from remote coordinate frame to remote coordinate frame. IE the prediction, observation from remote coordinates are frame dependent. The remote coordinate evaluations are global in nature so they take into account the spacetime curvature over the entire path. So for the Minkowski coordinates the speed of light is

dr/dt=1 [c=1] [invariant 1].

And for the remote bookkeeper Schwarzschild coordinates

dr/dt=1-2M/r [when r=2M, the event horizon dr/dt = 0]. The remote coordinate speed of light is frame dependent and can vary.

An experimental test for this would be the Shapiro Delay experiments.

 

[Write4U]

You might think about what Grumpy is saying. In local frames of reference the speed of light is an invariant c and travels in a straight line [since local coordinates are 'everywhere in the universe' light always travels in a straight line]. That's the natural path of light over flat spacetime. We can evaluate this path with the Minkowski metric [the metric of flat spacetime].

That seems to agree with what I am saying.

If we choose to evaluate a 'spacetime event' from remote coordinates the evaluation depends on those specific coordinates and the evaluation can change from remote coordinate frame to remote coordinate frame. IE the prediction, observation from remote coordinates are frame dependent. The remote coordinate evaluations are global in nature so they take into account the spacetime curvature over the entire path. So for the Minkowski coordinates the speed of light is

dr/dt=1 [c=1] [invariant 1].

And for the remote bookkeeper Schwarzschild coordinates

dr/dt=1-2M/r [when r=2M, the event horizon dr/dt = 0]. The remote coordinate speed of light is frame dependent and can vary.An experimental test for this would be the Shapiro Delay experiments.

Yep exactly as I tried to describe it. The bolded section confirms my assertion that "c" is constant and invariant and any "apparent" variance is the result of external conditions and potentials, but cannot be part of the potential of a photon. ("c")

 

[Grumpy]

forrest noble

The same things were going on before their perception, there was just no intelligence to conceive of time or give a name to it.

But the thing we are describing with that name(time itself)is real, even if our name is a concept. That's my point about not conflating the map(our name)with the thing that made the name necessary(time itself). They are two different things, time is real, our name is a construct that describes that real thing.

Of course your statement is just a matter of different possibilities of theory. In my view there is, and only ever could be just one universe: the one we live in -- with no reason to expect variations of it, or that it could have developed otherwise. Again there are many different views, hypothesis, theories, on this.

We only know of one Universe, and it is exceedingly empty of matter, I've read estimates of several proton's mass per cubic yard on average and always falling further. But who really knows. We wouldn't see matter except for it's gravity and the resulting clumping and fusion.

The influence of gravity causes time to dilate within matter, as does the motion of matter relative to the center of gravity in its location.

Gravity is acceleration, both dilate gravity exactly the same way, but gravity is motionless acceleration. And relative motion through spacetime dilates light all by itself, no gravity needed.

Grumpy

 

[forrest noble]

Sometimes "concepts" can in time be thought of as realities. I see this the case with space/time.
I still see the Einstein quote as supporting the reality space/time, if they have no separate existence from matter.

Yes, that's true. Separate from both time and space spacetime is its own indispensable concept.

I believe my explanation of spacetime may be the simplest, but for this reason a minority opinion of it. My concepts of reality in general are that everything in it can be simply explained. Of course my explanations may be simple and understandable but only some would agree with them

As to reality, I agree with the philosophers when they say that there is no absolute reality. Everything is organized and viewed from different perspectives of it.

As to spacetime, below is the simplest explanation of it IMO: Spacetime:

To explain the location of points in space we use several present methods of doing so. The two best known are the Cartesian coordinate system, which explains locations according to analytic geometry using the X,Y,Z coordinate system. And the other system is a telescopic coordinate system using an X and Y arc-angle system with a Z depth coordinate. Both systems rely on a point of origin in space from which to make measurement. There are usually two objects in space needed. Sometimes two stars in our galaxy, or in the distant universe maybe two quasars. One often defines the point of origin and the other the X or Y axis. Using either system we can define any point in space using these three coordinates, But how about next year or in the next ten years? Can we rely on the same coordinates? After all the stars and quasars are moving relative to each other as well as the background of stars in general and the distant background of galaxies. For this reason we must include the coordinate of time into our equations. We can make predictions of the relative motions of stars over time and predictions of motions of quasars over time, as well as predictions of the objects we are observing. If we put all these predictions into equations vector quantities and include time, we might be able to consider a point in space and time years from now as being close to the same position as it was ten years earlier. To do this we introduce the simple concept of spacetime, the location in space at a selected point in time, such as a time in the past, present, or future. This system of measurement is called Minkowsky spacetime.

To me this concept of spacetime is a simple concept like both the concepts and definitions I provided of time and space separately, and again there is much disagreement concerning a consensus explanation of spacetime, as there are disagreements concerning definitions and explanations of either time and space separately. If you would ask me to explain something concerning physics, my opinion would often be that the simplest presently acceptable explanation of it is more likely to be correct.

Rutherford was my hero in this regard when he said: If you can't explain your physics to a barmaid it's probably not very good physics. "If you can't explain your physics to a bartender it's probably no damn good." "If you can't explain your research to the cleaning lady, it's not worth doing." and "if you can't explain your research in layman's terms, you probably don't understand it yourself."

Einstein had a funny related quote himself when he said:

"Make things as simple as possible, but not simpler." ... Dubbed 'Einstein's razor.

 

[brucep]

That seems to agree with what I am saying.


Yep exactly as I tried to describe it. The bolded section confirms my assertion that "c" is constant and invariant and any "apparent" variance is the result of external conditions and potentials, but cannot be part of the potential of a photon. ("c")

It's not your assertion it's fact of nature. There is no "apparent variance". It either varies or it doesn't. The measurements and observations made from local or remote coordinates are just as valid. There are no external conditions. The spacetime event is either evaluated from local coordinates or remote coordinates. So your explanation sounds good to you but not to me. The key is measurement and observation are 'real' regardless the coordinate system used to describe the spacetime event.

 

[forrest noble]

forrest noble

But the thing we are describing with that name (time itself) is real, even if our name is a concept. That's my point about not conflating the map (our name) with the thing that made the name necessary (time itself). They are two different things, time is real, our name is a construct that describes that real thing......

Your point is valid, that the actions which define time are a reality. The contention that time is a separate entity from either matter or field is debatable however. I choose the perspective that intelligence organizes time as an explanation for the rate that reality changes.

 

[PhysBang]

Rutherford was my hero in this regard when he said: If you can't explain your physics to a barmaid it's probably not very good physics. "If you can't explain your physics to a bartender it's probably no damn good." "If you can't explain your research to the cleaning lady, it's not worth doing." and "if you can't explain your research in layman's terms, you probably don't understand it yourself."

This is too high a bar to ask of someone is a very technical job.

 

[Write4U]

Your point is valid, that the actions which define time are a reality. The contention that time is a separate entity from either matter or field is debatable however. I choose the perspective that intelligence organizes time as an explanation for the rate that reality changes.

I maintain that time emerges (is created) with change. Without matter "time" would be a meaningless term and without time there would (could) be no matter. Both come into existence at the same "instance", i.e. a physical event (change) which becomes "historically fixed" at a spacetime coordinate.

 

[Grumpy]

Write4U

I maintain that time emerges (is created) with change. Without matter "time" would be a meaningless term and without time there would (could) be no matter. Both come into existence at the same "instance", i.e. a physical event (change) which becomes "historically fixed" at a spacetime coordinate.

Yet we have the observed fact that the more matter and energy in local spacetime the slower time goes(dilation), to the point that time stops at both the Event Horizon of a Black Hole and at lightspeed. From that extreme point time flows faster with LESS matter and energy. When you get to very low(but not zero)energy levels time flows it's fastest. So what mechanism then turns time off when at it's fastest just because that last little erg disappears? And what mechanism causes time to go from non-existence to full speed when a single Quantum of energy arrives? Your paradigm does not fit the facts. Rather than non-existence in empty space, time runs at it's fastest rate in the absence of dilating mass or energy. So it exists independent of whether mass does, even though it is affected when it does.

Time is a dimension every bit as valid as one of any other distance. You can see the past(in fact that is all you can see, simultaneity is an illusion cause by the very short distance in time of the things close to you, they too are in the past), it is a distance in this Universe. We do not see the Universe as it is in the present(even the sun is 8 minutes in your past), we see it as it was in increasing distances into the past. Time is very real and is a characteristic of spacetime, which is what our Universe is. Matter and energy affect spacetime, but like a water balloon, there is a container(spacetime)and a contained(energy and matter), and while the water inside the balloon distorts the balloon, it is not the same thing as the balloon. Nor does it create the wall of the balloon by needing to be contained.

Here's an exercise to show how spacetime is one thing. Describe how you would return to Earth's surface from a trip to Mars and back. You know the Earth's orbit, but if you guess wrong you could end up 186 million miles away from your target on the other side of that orbit. So how would you designate the position you need to reach? You must specify where the Earth will be at the position in it's orbit. In other words, it takes not only coordinates in the three dimensions of space, but also one of time. That's Earth's position in 4D spacetime. Time is measured by motion or change, but it is not created by motion or change, they only slow it down.

Without matter "time" would be a meaningless term

Are you laboring under the delusion that "meaning" is a concern of the Universe? Just because we cannot measure something does not mean it ceases to exist. Time is, whether you can extract meaning from it or not. Motion let's us extract meaning from time, just like a well let's you extract water from the depths. Do you think the water is not still there when you are not near a well? That's the logic you are trying to apply to time. Time is not a characteristic of matter, it is a characteristic of the Universe itself.

Grumpy

 

[PhysBang]

Yet we have the observed fact that the more matter and energy in local spacetime the slower time goes(dilation), to the point that time stops at both the Event Horizon of a Black Hole and at lightspeed.

Neither of these is an observation. Neither is true. Time never slows down to nothing, as far as we can tell and time certainly does not slow down to a stop for GR. There can be an ever increasing time dilation relative to a given system of coordinates, but there is always a system of coordinates in which there is no time dilation (though there are possible terminal paths). I'm not sure what it means for time to be stopped at lightspeed, since light does get from place to place.

 

[brucep]

Neither of these is an observation. Neither is true. Time never slows down to nothing, as far as we can tell and time certainly does not slow down to a stop for GR. There can be an ever increasing time dilation relative to a given system of coordinates, but there is always a system of coordinates in which there is no time dilation (though there are possible terminal paths). I'm not sure what it means for time to be stopped at lightspeed, since light does get from place to place.

You could review what the remote bookkeeper coordinates predict. To determine these predictions/reckonings/observations/measurements are just as valid 'physics' as the invariant predictions/reckonings/observations/measurements associated with local coordinates [where the spacetime event occurs]. One is invariant [true] and the other is frame dependent [true specifically to those coordinates]. The first part of your comment is equivalent to saying the 'only' valid physics is conducted in local frames of reference. I don't think that's what you had in mind. The following is an example of valid frame dependent physics. This is one of 'my' favorites.

Joe Dolan [via the remote HST coordinates] observes the first recorded 'dying pulse train' predicted by the Schwarzschild remote bookkeeper coordinates.

http://hubblesite.org/newscenter/archive/releases/exotic/black hole/2001/03/text/

Re-enactment of the observed dying pulse train predicted by the remote bookkeeper coordinates.

http://imgsrc.hubblesite.org/hu/db/videos/hs-2001-03-a-low_mpeg.mpg

 

[Grumpy]

PhysBang

Neither of these is an observation. Neither is true. Time never slows down to nothing, as far as we can tell and time certainly does not slow down to a stop for GR. There can be an ever increasing time dilation relative to a given system of coordinates, but there is always a system of coordinates in which there is no time dilation (though there are possible terminal paths). I'm not sure what it means for time to be stopped at lightspeed, since light does get from place to place.

So time is not more dilate(slower)on the surface of the Earth than it is far from mass(careful, both have been accurately measured, IE they have been observed)? Time slows to a stop for anything at lightspeed, it's been accurately measured in the LHC that at very close to lightspeed particles travel much further than their known lifetimes at non-relativistic speeds would allow and the closer to lightspeed the slower their time goes, the shower of particles from a Cosmic ray does reach the ground(it shouldn't). Time dilation due to speed is well evidenced. So is time dilation due to mass. So how is it you think those things aren't true? I don't know where you got the idea that physicists have just been sitting on their hands for the last one hundred years, but it is not true, we've been busy observing and confirming the things Einstein said and they are true, they describe the reality we see. And Relativity says time stops(for the frame in movement)at a certain level of acceleration/gravity, and at a certain speed. And that is what we see. That no mass can ever reach lightspeed means time can never completely stop for the speed of mass, but photons experience no time at all. But the event Horizon stops time completely, no event inside that horizon will ever experience a moment of time in this Universe. A traveler entering a BH will be seen to move slower and slower as they approach the horizon, never quite reaching it and disappearing into redshift, but the traveler would not notice any change in his time rate. So, yes, you can always find a frame that has no evident time dilation, we call that frame the local or comoving frame. It never varies in any obvious way as brucep pointed out. Every observer sees themselves as the "norm", it is only outside observers that see the dilations and distortions in a frame and even that is all relative. The slope of time dilation is clear, the more mass, energy, acceleration or speed the frame has, the slower time goes, so the corelary is that the less mass, energy, acceleration or speed the less time is dilated. THESE ARE OBSERVED FACTS. Extrapolating to the endpoints gives you speed or acceleration high/slow or stopped time to speed or acceleration low/fast time, yet you suggest the end point of empty space has no time at all. What causes time's rate to go from the maximum rate to full stop/non-existence when the last Quantum of energy leaves? How much energy does it take before time slams back to maximum, undilate rate from a dead stop?

And the propagation speed of electromagnetic phenomena through spacetime is c. It is built into the Universe and never moves at any other speed. That is just one of the properties of spacetime, I'm afraid.

Grumpy

 

[Aqueous Id]

I maintain that time emerges (is created) with change.

"Change" is not a very good word since we talk about gradients, which are changes in a parameter over any dimension in general, not just time. Thus the temperature of ocean water changes over depth rather than time, air pressure changes with altitude, or the strength of a field changes with distance between emitter and detector.


That being said, there is evidence that spacetime is perpetually being created, which begins with Hubble's observations of the expanding universe. That is, space and time are both being created, it would seem, without any other cause. This is consistent with the way we describe changes in any parameter q with respect to time: dq/dt, or with respect to space: dq/dx + dq/dy + dq/dz, or both. It's therefore more logical to say that any change in any parameter is always referenced to a change along the axis of some dimension.

Without matter "time" would be a meaningless term

Not necessarily, since energy can exist as light (photons) which literally illuminate space and time.

and without time there would (could) be no matter.

More to the point there could be no matter without space.

Both come into existence at the same "instance", i.e. a physical event (change) which becomes "historically fixed" at a spacetime coordinate.

That won't account for the perpetuation of time because matter can't be created anymore. Nor is there any observation to conclude other wise. What's observed is that space is being created. So the best answer is probably just to say space and time are being created out of the Big Bang itself, that we are still Banging, just in a highly condensed epoch already shaped by billions of years of cosmic evolution.