I Why is there a universal speed limit, c, and why is it what it is?

[GrayGhost]

I am asking why there is a "universal velocity c."

Why is there a c? Why is there a speed limit to the universe? Why is there a limit to how quickly a cause can follow an effect at distance? Why is there a "causality constant"?

What is(are) the limiting factor(s) that make it what is? The speed limit is a consequence of what? Is what we know to be the speed limit the result of measurements? Or is it a logical problem that can be figured out in a thought experiment?

CosmicVoyager,

All very good questions :)

To be frank, no one (anywhere) has answered these questions to date in any satisfactory way. Nor have I. When one does, a nobel prize sits begging.

One fellow here brought up geometry as a fundamental root of this. That's a reasonable and fundamental statement I suppose, but it doesn't answer the question.

Here's my opinion on the matter ...

Relativity theory suggests we all travel thru the continuum at the equivalent of c. This suggests that what we measure as "the relative velocity between material entity" is the result of unparallel speed-c velocity vectors thru the continuum. If parallel, then they are at rest with each other.

The next question is this ... Why would we travel thru spacetime at c?

I would suggest that the answer here may relate to "spacetime expansion". It could be that light does not move at all, that it only appears to move, because we move thru spacetime at c. This is no different than each of 2 inertial starships assuming themself the stationary and the other in motion, and both being correct. It's all relative. Anywho, food for thought.

GrayGhost

 

[nitsuj]

DaleSpam RE: post 86.

I didn't recognized it as a question because it is not a...nvm.

I misunderstood you dalespam, seems you have clarity beyond understanding. :)

 

[nitsuj]

CosmicVoyager,

All very good questions :)

To be frank, no one (anywhere) has answered these questions to date in any satisfactory way. When you do, a nobel prize sits begging.

One fellow here brought up geometry as a fundamental root of this. That's a reasonable and fundamental statement I suppose, but it doesn't answer the question.

Here's my opinion on the matter ...

Relativity theory suggests we all travel thru the continuum at the equivalent of c. This suggests that what we measure as "the relative motion between material entity" is the result of unparallel speed-c vlocities thru the continuum. If parallel, then they are at rest with each other.

The next questions is this ... Why would we travel thru spacetime at c?

I would suggest that the answer here may relate to "spacetime expansion". It could be that light does not move at all, that it only appears to move, because we move thru spacetime at c. This is no different than each of 2 inertial starships assuming themself the stationary and the other in motion, and both being correct. It's all relative. Anywho, food for thought.

GrayGhost

I kinda agree,
If time stops at C, and space is time, then is it not true at C you are in the same space as you were previously so nothing changes, ie no time? RETORICAL.

It makes sense to me. Objects cannot exist in the same space another object occupies, if it could wouldn't that mean there is no time between them? RETORICAL.

 

[Huttate]

Keep thinking. Remember this spacetime malarky very nearly sent Albert over the edge, and they never Nobel'd him coz they thought it wacky.

It takes a new pair of eyes - and probably a young pair if history is any guide - to see it from a different angle.

But do keep thinking, otherwise you are just repeating the words of the wise and we all know they are not fundamentally right in all aspects of the universe in which we live.

 

[GrayGhost]

If time stops at C, and space is time, then is it not true at C you are in the same space as you were previously so nothing changes, ie no time?

It makes sense to me. Objects cannot exist in the same space another object occupies, if it could wouldn't that mean there is no time between them?.

I'm not quite sure how this applies to what I stated, however no 2 material entities can occupy the same space. Even if an observer could magically accelerate to relative c, he would not co-occupy space with other-normal-speed-heavenly-bodies. If he ever does, he collides, and that would be a huge mistake on his behalf (and the other's).

GrayGhost

 

[nitsuj]

Both your idea and mine share spacetime itself as moving, you didn't derive that from what I said, I'll try agian.

I didn't even remotely say that something traveling at C would "co-occupy" space with a slower moving object. In fact I feel poisoned having been associated with that remark.

The second RETORICAL question you replied to was to isolate the idea of C being the reason for time stopping.

(the glass of milk on my counter will go bad fairly soon, maybe by tommorow, my chocolate milk mix won't, it has a much longer shelf life. Now if I put this chocolate milk mix into the milk, time between them is now irrelevant, my chocolate milk mix that is in the milk will spoil lock step with the milk. that's another way to very loosley describe what i was saying about occupying the same space and there being no time between them. as far as the spacetime I can see those two items now occupy the same spacetime, if you notice the beverage is sweet and nutritious at the same time, miraculous, making healthy food pallatable by eliminating the time between the experience of it and tastey food lol, chocolate milk time traveling in action, okay I've gone too far now :)

 

[bobc2]

...In other words, there is a mechanism inside the ball, which we could develop a mathematical model for that would predict observations, but because a model already exists that predicts without a complete description of all structure, they have no interest in doing so. That is sufficient for practical applications, but people want to fully understand the structure of the universe.

CosmicVoyager, while I certainly appreciate the concept DaleSpam has communicated to us, I really seriously tried to present a picture of a mechanism ("inside the ball") resulting in a limiting value for the speed of an object. I really presented this picture as a serious candidate for answering the question, "Why does speed have a limiting speed, namely the speed of light?" I'll present the graphics again because I think it is a reasonable picture of the situation. I could explain this in more detail, but it would take an unreasonable amount of space here. The picture should not be dismissed as just graphics.

To appreciate the picture a person of course is going to have to develop some concept of a 4-dimensional universe and be able to interpret a spacetime diagram in that context. I can do a tutorial in a different thread if need be (or folks can google "spacetime diagram"). My diagrams are intended to be fairly literal picture models of observers moving at relativistic speeds and "living" in a squence of 3-D cross-sections of a 4-D universe. If one really wants to pursue your "why" question, they should first pursue an understanding of spacetime diagrams if they do not already have a grasp of special relativity.

First of all, just this one fact alone, namely that the X1 axis rotates symmetrically toward the X4 axis for increasing speeds, is adequate to explain why all observers measure the same speed for light. You should be able to see directly in all of the pictures below of different observers with different velocities that the ratio of X1 to X4 is the same for each one of those pictures. This is a definite answer to the question about same light speed for all observers. (It's as good a "Why" answer as you would get about the blue sky.)

Again, the sequence of 4-D pictures below (X2 and X3 supressed) are a serious attempt at demonstrating why there must be a limiting speed. Once understanding this, an even more burning question of physical reality arises: WHY does an observer's 3-D cross-section view (the X1 axis) of the 4-D universe continually rotate so as to eventually converge on the 4th dimension (X4 axis)? This seems to be the more fundamental question, because again, that magical rotation leads to the limiting value (X1 and X4 axes converging in the limit).

In other words, if the model below, as implied by special relativity, is accepted as a working model, we could then proceed to the next "why" question: "Why does the X1 axis rotate?" (Note that in Newton's model of the universe, the X1 axis never rotates--but then experiments have shown that Newton's model does not work at relativistic speeds).

 

[Dale]

I didn't recognized it as a question because it is not a...nvm.

D'oh! I quoted it a half-dozen times and never noticed that it wasn't actually a question.

 

[nitsuj]

At least it wasn't your point. And I retract my comment from the same post "I misunderstood you dalespam, seems you have clarity beyond understanding. :) " .

 

[Dale]

For example, if you were right, Newton's work on mechanics was a failure*.

Why on Earth would you say that? He came up with an amazingly simple mathematical model that is still in use more than 3 centuries later due to its simplicity and accuracy.

I don't think that it is "pessimistic" to understand the limitations of the scientific method. It is not a magical crystal ball, nor the mythical oracle, it has limitations and it is good to understand those limitations. There is nothing pessimistic nor optimistic in that understanding, it just is an understanding of the nature of a valuable tool.

 

[nitsuj]

bobc2 "WHY does an observer's 3-D cross-section view (the X1 axis) of the 4-D universe continually rotate so as to eventually converge on the 4th dimension (X4 axis)?"

That is some writing worthy of publishing. Just tickles my brain lol

Some annimation of that happening would be wicked.

 

[CosmicVoyager]

@bobc2

I should have replied the first time to say thanks and that I find it difficult to convert the graph into visualizing what is happening in 3D. What I would like to see is an animation of a photon in a 3D grid, or an illustration with 2D representing 3D and 3D representing time. You seem to be saying the universe is changing shape, which it obviously cannot be doing since it would require the universe to simultaneously have different shapes for every particle moving at a different speed. That is a direct contradiction.

 

[bobc2]

@bobc2

I should have replied the first time to say thanks and that I find it difficult to convert the graph into visualizing what is happening in 3D. What I would like to see is an animation of a photon in a 3D grid, or an illustration with 2D representing 3D and 3D representing time.

Let me think about that and see if I can figure out a way to do a better job of communicating.

You seem to be saying the universe is changing shape, which it obviously cannot be doing since it would require the universe to simultaneously have different shapes for every particle moving at a different speed. That is a direct contradiction.

I think I fully agree with you. But, I must be cardful that we are talking about the same universe. When I think of the universe not changing shape, I'm picturing the 4-dimensional universe. But, with the so-called "block universe" model the observers experience a continuous sequence of new cross-sections of the 4-dimensional universe. And this does mean that observers moving at different speeds would, at any instant of time, be "living" in different 3-D universes. And that would certainly be contradictory if it were not for a model that feature a 4-dimensional universe populated with 4-dimensional objects (including the 4-dimensional bodies of the observers). I really hesitate to carry the description much further for a number of reasons, but can if you wish. But the 4-D picture is pretty much as shown in the earlier sketches. After a while I'll throw up one more graphic to make the picture a little more complete.

 

[nitsuj]

Let me think about that and see if I can figure out a way to do a better job of communicating.

I think dalespam and bobc2 should become friends. :)

 

[CosmicVoyager]

I think I fully agree with you. But, I must be cardful that we are talking about the same universe. When I think of the universe not changing shape, I'm picturing the 4-dimensional universe. But, with the so-called "block universe" model the observers experience a continuous sequence of new cross-sections of the 4-dimensional universe. And this does mean that observers moving at different speeds would, at any instant of time, be "living" in different 3-D universes. And that would certainly be contradictory if it were not for a model that feature a 4-dimensional universe populated with 4-dimensional objects (including the 4-dimensional bodies of the observers)..

If time is one of those dimensions,and each particle is a cross section, wouldn't that require 5 dimensions? Because with only 4 the fourth has to be either the sequence of cross sections which would still require an additional dimension for time, or the fourth be time and no cross sections for each particle?

 

[bobc2]

If time is one of those dimensions,and each particle is a cross section, wouldn't that require 5 dimensions? Because with only 4 the fourth has to be either the sequence of cross sections which would still require an additional dimension for time, or the fourth be time and no cross sections for each particle?

In this model you don't need a dimension for time. I am considering only spatial dimensions as containing 4-dimensional objects. We refer to time as a parameter. Below is a sequence of sketches that attempts to clarify that idea. The toughest aspect of this model to wrap your mind around is the part that has an observer moving along the 4th spatial dimension at the speed of light. In lower left sketch, C, I've shown a solid curved bar object with two ends fixed in the ground. Perhaps it is night time (to make the illustration easier). A beam of light is focused on the bar, and the light source is moved in just the right way to make the light spot move along the length of the curved beam at a constant speed along the beam (speed tangent to the beam). Time is used as a parameter--we can tell what time it is at each point along the beam that the light spot passes. That is, we could actually mark off time values along the beam that records the time at which the light spot passed each point on the beam. The bar really extends along a 3-dimensional path, and we could obviously establish a spatial coordinate along the beam--we could use the regular X1, X2 coordinates (ground surface), but then use the path of the beam as the X3 coordinate. So, now we have three spatial coordinates, but we are using time as a parameter to keep track of where the light spot is along the beam, i.e., along the X3 coordinate. The reference to the 4th dimension as a time dimension, in my view, is a misnomer. I and many other physicists believe that the 4th dimension should be regarded as a purely spatial dimension (just like our curved bar X3 dimension in 3-D), but having a distance relation along the bar to parametric time.

So, the universe is actually 4-spatial dimensions, and time is something, associated somehow with consciousness. Just like the light spot moved along the 3-D curved beam, some aspect of observers (we don't know exactly what) moves like the light spot along the 4th dimension of the 4-D objects, and we use time as a parameter to locate our observational positions along the 4th dimension of observer body structures. Of course the body structures cannot move. They are static 4-dimensional objects--they don't move any more so than the 3-D curved bar anchored to the ground (just the light spot moves, and perhaps just some aspect of mind moves). (More later if you wish--but I'm afraid I am way too long winded.)

 

[CosmicVoyager]

IIn this model you don't need a dimension for time. I am considering only spatial dimensions as containing 4-dimensional objects. We refer to time as a parameter. Below is a sequence of sketches that attempts to clarify that idea.

Four spatial dimensions?! Now *that* changes everything! Someone was telling me something like this before but they were saying time was one one the dimensions. I knew it could not be done with just 3 spatial dimensions! Let me think about this.

 

[CosmicVoyager]

@bobc2

Figure d is showing the fourth dimension to be time. It shows the big bang in one direction and the big crunch in the other. I thought there were going o be four dimension plus time. I'm back to the problem of where are the cross sections. How is there one for every particle? A cross section is 3D, right? And a series of 3D cross sections is 4D. So I don't see how there is a cross section for every particle. Each particle would only exist at one point in time. One 3D cross section per moment throughout the history of the universe.

 

[OnlyMe]

The speed limit is a consequence of what? Is what we know to be the speed limit the result of measurements? Or is it a logical problem that can be figured out in a thought experiment?

I just dropped in on this forum today. It seems several of the posts I read kind of skated around a direct answer. Mostly because other than in theory or hypotheses, no one really knows why c is a velocity limit.

That said... The speed of light as a speed limit most likely is a consequence of Einstein's (AE) 1905 paper (On the electrodynamics of moving bodies) introducing special relativity. And was drawn from connecting a the work of a number of others.

Piece 1. Earlier that year AE published a paper on Brownian motion, an argument in support of the existence of atoms. The idea of atoms had been around for a long time but his paper essentially crystalized the concept. Aside from electrons, no other subatomic particles were known at the time.

Piece 2. In the first or second paragraph of his paper introducing special relativity, he mentioned failed experiments to discover the motion of the Earth relative to the light medium, an assumed reference to the Michelson & Morley experiments and then later essentially discarded the concept of the ether completely.

Piece 3. There had been experimental evidence establishing the velocity of light in a variety of mediums -- solid, liquid, gaseous and vacuum. The speed of light in vacuum was in close agreement with the work of Maxwell, on electrodynamics.

Piece 4. In the first section of that paper, Kinemetical Part, Part 1. Definition of Simultaneity, he asserts, "In agreement with experience we further assume the quantity 2AB/(t'-t)=c, to be a universal constant--the velocity of light in empty space."

conclusion: Empty space and a vacuum, the abscence of atoms, were assumed to be equivalent. No ether and with no knowledge of anything other than atoms, empty space was a vacuum. The speed of light in a vacuum is c. The speed of light in empty space is c.

Nothing has been observed to have a greater velocity than c. The speed limit aspect most likely came much later and probably from interpretations of the E=mc^2 formula, which suggest that it requires an infinite amount of energy to accelerate an object having mass to the speed of light.

The above give at least one answer to how c came to be accepted as a limiting velocity. It still does not say why.

 

[Dmitry67]

Relativity theory suggests we all travel thru the continuum at the equivalent of c. This suggests that what we measure as "the relative velocity between material entity" is the result of unparallel speed-c velocity vectors thru the continuum. If parallel, then they are at rest with each other.

It is a result of our spacetime being (locally)pseudoeuclidean (+++-)
So the original question falls into the same category as 'Why there are 3 (macroscopic) space dimesions?'

 

[bobc2]

@bobc2

Figure d is showing the fourth dimension to be time. It shows the big bang in one direction and the big crunch in the other. I thought there were going o be four dimension plus time. I'm back to the problem of where are the cross sections. How is there one for every particle? A cross section is 3D, right? And a series of 3D cross sections is 4D. So I don't see how there is a cross section for every particle. Each particle would only exist at one point in time. One 3D cross section per moment throughout the history of the universe.

No. Figure D is showing a 4-dimensional universe. The whole universe is all there, all four dimensions of it, frozen in time. You see the 4th dimension coordinate labled X4--that's the direction of the 4th spatial dimension. I label one instant of time as "NOW." But, remember time is just a parameter used to mark off points along the 4th dimension as the yellow spot on the diagram moves along the static 4-dimensional world line at the speed of light. Time is something perceived by that yellow dot as it moves along the 4th spatial dimension (just like the example of the light spot moving on the curved beam in the earlier sketch).

We use phrases like, "The big bang happened at the creation of the universe." That satisfies our stubbornly persistent subjective conscious feeling that things happen. That derives from our conscious experience--again associated with the yellow spot moving along our bundle of neuron fibers that are stretched out for billions of miles along the 4th dimension--as though the mind is watching a movie as it moves along the sequence of 3-D images presented by the 4-D neurons.

I hate to have to present things in this way, because there are some very unpleasant discussions that are evoked--and some even more unpleasant implications coming out of this kind of picture. But, once this picture is grasped, it hopefully helps crystallize some of the fundamental issues of special relativity. And it leads ultimately to "why" questions beyond the realm of physics. A great physicist who passed away a number of years ago, Bryce DeWitt (Univ of North Carolina and Univ Texas), made the statement in a "Physics Today" article that, "...there is much more to reality than physics."

 

[Dmitry67]

I know another great physicist, Max Tegmark, who is alive, and his famous MUH program. When I first read it I was shoked and for 2 weeks was not able to think about anything else.

He has an opposite view - that on the very fundamental level, there are just equations, and the size of how he calls it "word baggage" is exactly 0.

For me he was able to asnwer all "Why" questions here:
http://arxiv.org/abs/0704.0646

 

[Dale]

Nice reference. Particularly "if there is an isomorphism between a mathematical structure and another structure, then they are one and the same. If our external physical reality is isomorphic to a mathematical structure, it therefore fits the definition of being a mathematical structure."

The lack of word baggage would, of course, necessarily exclude word questions, which I like.

 

[Dmitry67]

There is a second interesting part in the same article.
Say, we have TOE equations with no "word baggage"
Max asks "But WHY these equations, not another?" or "What burns fire in these particular equations?" and answers them starting from p16.

 

[Calrid]

There is a second interesting part in the same article.
Say, we have TOE equations with no "word baggage"
Max asks "But WHY these equations, not another?" or "What burns fire in these particular equations?" and answers them starting from p16.

The debate about maths being the underlying structure of reality and reality being the underlying structure of maths is an interesting one, ie does maths have an existence in and of itself or is it an abstraction. But I'm not sure it is going to be resolved in physics or maths by this paper. I'll have to take a look later. I personally see mathematical models as an approximation of reality that has some lower bound where it is accepted as being close enough so that there is no distinction. But meh whatever floats your metaphysical boat.

The only baggage I can see is faulty assumptions, maths or English or Swahili is beside the point.

 

[bobc2]

I know another great physicist, Max Tegmark, who is alive, and his famous MUH program. When I first read it I was shoked and for 2 weeks was not able to think about anything else.

He has an opposite view - that on the very fundamental level, there are just equations, and the size of how he calls it "word baggage" is exactly 0.

For me he was able to asnwer all "Why" questions here:
http://arxiv.org/abs/0704.0646

Yes. I've studied his ideas. And he has developed a remarkable concept with solid rationale. I particularly admire him for his guts in laying it out there (MIT of all places) in an environment not suited for out-of-mainstream avant garde stuff. He has taken some heavy incoming from some in the physics community at times.

I'm personally still carrying the "baggage" but still very much admire his work. Thanks for calling attention to him, Dmitry67. I think your admiration and excitement over his ideas is well placed. Once you buy into his reality, then you've answered lots of "why" questions.

 

[nitsuj]

lol, you mean to say the Cohen brothers have it right?

Morpheus: Unfortunately, no one can be told what the Matrix is. You have to see it for yourself.

 

[Dmitry67]

bobc2, I am happy we are on the same page.

May be you have heard about... well, I even don't know what to google.

There are dimensionless parameters of the standard model. (and also density of Dark Matter and Energy). What happens if we change these parameters? Will life be possible or not? If not, what will be the weakest link in a chain (galaxy formation, stellar evolution, planet formation, chemistry, existence of self-replicating molecules etc)? That work of different scientists will help us to draw a ‘map’ of the ‘island of life-friendliness’ of the Universe. The questions I am interested are:

How big is that island?
Are we in the center or closer to the ‘seashore’?
Are the any other separate ‘islands of life-friendliness’? (may be based on another chemistry)?

 

[bobc2]

DaleSpam is right.
But just 2 cents.
Science is capable of answering "Why" questions (only to some extent) - using the Anthropic principle

http://en.wikipedia.org/wiki/Anthropic_principle

Remember your earlier Anthropic Principle link? There are so many examples of properties and conditions in the universe that defy expectations, but are absolutely necessary for life.

My favorite example is the highly unlikely circumstance of an obscure excited state of the Carbon 12 nucleus having just the magically correct resonance that provided a way to synthesis of the normal Carbon 12 configuration (there would be no way to synthesize the remaining periodic table without first synthesizing Carbon 12--it is the bridge from He and Be to the rest of the elements) . But Be-8 could only combine with He-4 if the resulting Carbon nucleus matched the combined energy--only possible if there existed an excited state of C12 (analagous to an isomer) that matched the Be-He combination.

The story told by Simon Singh in his book, "Big Bang" about how Fred Hoyle speculated that there had to be a special excited state with just the right energy is priceles! Hoyle calculated the required resonance and pestered William Fowler at Cal Tech mercilessly until he agreed to run an experiment in search of the resonance--Fowler couldn't believe it was right where Hoyle predicted it (7.65 MeV more energy than the normal C12 state). But what an enormous unlikely but fortunate outcome for life that nature prepared that special configuration of the Carbon nucleus.

 

[SeventhSigma]

Too lazy to read this thread so I am very sorry if I am repeating anyone.

I would assume c is what it is because of, partly, the anthropic principle. In our particular universe, everything is structured in such a way (composed of atoms/quarks/electrons/particles/etc) under certain laws with various constants such that c is a mathematical eventuality and necessary condition arising from relativistic symmetries of space and time.

For instance, E = mc^2 is really just a form of conversion. We write it this way because we've defined energy/mass/speeds in various metrics. Let's just hold the speed of light c to equal 1 in natural units (which is to say, instead of defining c as 300,000 of something else of value 1, let's just define c as our fundamental unit of 1 to begin with). Then we simply see that E = m only we're discussing both E and m in different units.

The real question isn't so much "why is c equal to 300 km per second" but why is E = m in the first place. Understanding this can help explain the relative ratios of how everything in our universe relates, which in turn helps to explain why c has the value it does relative to other things.

IMO, when it comes to our cosmos, it all comes down to the ratios and conversions inherent in our universal properties. Given certain ratios/conversations necessary to sustain a stable, functional universe with working laws, the mathematics and values/properties of other phenomena emerge as necessary conditions/eventualities.