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Author Topic: Speculation on the value of c?  (Read 8205 times)

Offline Dick1038

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Speculation on the value of c?
« on: 01/12/2007 01:55:30 »
Is there any speculation or theory on why c=300,000 km/sec(approx) and not some other value, like, 150,000 km/sec or 600,000 km/sec?  What determines this cosmic speed limit anyway?

The age of the universe is about 14 by.  The farthest distance that astronomers have detected galaxies is about 14 bly.  Is there any explanation for this numerical coincidence?

Just wondering.


 

another_someone

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Speculation on the value of c?
« Reply #1 on: 01/12/2007 02:42:09 »
Is there any speculation or theory on why c=300,000 km/sec(approx) and not some other value, like, 150,000 km/sec or 600,000 km/sec?  What determines this cosmic speed limit anyway?

It used to be possible to speculate on why the speed of light is exactly 299 792 458 m/s; but no more - they have defined the metre as being 1299 792 458 of a light-second, so the speed of light is now written into stone, and no amount of scientific measurement can change it.

Since light is an electromagnetic wave, in classical (pre-relativistic) physics, this speed can be deduced by knowing the permeability and permittivity of free space, and so knowing how the electrical and magnetic components of the wave will interact with each other.  Ofcourse, this brings us back to why the permeability and permittivity of free space should be the values that they are.

The age of the universe is about 14 by.  The farthest distance that astronomers have detected galaxies is about 14 bly.  Is there any explanation for this numerical coincidence?

Just wondering.


It is not a coincidence - it is a necessity.

If the speed of light is finite (which all evidence says it is), then if the universe was created at time X, then the furthest we can see is the distance light could have travelled since time X.  If the universe was created 14 billion years ago, then no light could have been created before 14 billion years ago, so we could not see anything older than 14 billion years ago.  As when we look into space, we are looking at old light (i.e. when we look at something that is 1 light year away, we are looking at light that was emotted from that object 1 year ago, and took 1 year to travel to our eyes), so when we look at something that is 14 billion light years away, we are looking at light that was emitted 14 billion years ago, and took 14 billion years to reach our eyes - so it is clear, if there was no universe 15 billion years ago, so we cannot possibly see anything that emitted light 15 billion years ago - yet for the light from an object 15 billion light years away to reach our eyes today, it would have had to leave its source 15 billion years ago.
 

Offline ukmicky

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Speculation on the value of c?
« Reply #2 on: 01/12/2007 20:22:31 »
Quote
so when we look at something that is 14 billion light years away, we are looking at light that was emitted 14 billion years ago



Hi George

Sorry but for above to be correct we would have to reside in a static universe.

A photon released from a star in a galaxy that was say 10 billion light years away from us 10 billion years ago would take more than 10 billions years to reach us because the space in between us and the star would have dramatically increased over 10 billion years especialy as recession velocities can exceed c.

The way i see it and tell me if i'm wrong but its possible that their is light released by some stars that were only 5 billion light years away from us a few billion ly ago that has never and will never reach our planet if the expansion of the universe continues on its present path.. And therefore the limit to how far we can see is not the age of the universe but must be the speed of expansion.
« Last Edit: 02/12/2007 00:10:58 by ukmicky »
 

another_someone

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Speculation on the value of c?
« Reply #3 on: 02/12/2007 03:23:57 »
Quote
so when we look at something that is 14 billion light years away, we are looking at light that was emitted 14 billion years ago

Hi George

Sorry but for above to be correct we would have to reside in a static universe.

A photon released from a star in a galaxy that was say 10 billion light years away from us 10 billion years ago would take more than 10 billions years to reach us because the space in between us and the star would have dramatically increased over 10 billion years especialy as recession velocities can exceed c.

The way i see it and tell me if i'm wrong but its possible that their is light released by some stars that were only 5 billion light years away from us a few billion ly ago that has never and will never reach our planet if the expansion of the universe continues on its present path.. And therefore the limit to how far we can see is not the age of the universe but must be the speed of expansion.

Granted, I should have used past tense, since we have no idea where the galaxy might be today, but only that it was that far away when it emitted light that long ago, but by now could have moved a considerable distance further, or even closer (although the default assumption is that it would have travelled further away).
 

Offline Dick1038

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Speculation on the value of c?
« Reply #4 on: 06/12/2007 19:28:11 »
another_someone:  You've answered my question to my satisfaction. However, if the permeability of free space were different then c would be a different value, correct?  Does the stretching of space change the permeability?

ukmicky: Good point. So a photon emitted at a great distance would be gradually stretched out at a constant rate, so that wavelength is a function of The initial wavelength, expansion rate and time. Does that still mean that the red shift is proportional to distance?
 

Offline Soul Surfer

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Speculation on the value of c?
« Reply #5 on: 09/12/2007 12:24:10 »
That is an interesting question that has exercised my mind a bit.  Clearly if we were talking about some sort of normal solid liquid or gaseous material and we stretched it or squeezed it it would affect the velocity of sound propagating through it and so one might expect that the velocity of light through space might change as space expands.  This is clearly not observed throughout a very large scale in the universe and is also consistent for probing events at small spaces and times using accelerators.

There are to my mind three possible explanations for this.  I will state them in order of simplicity.

Firstly the expansion of space effectively involves the creation of more "elements of space" between objects and does not change the basic properties of space itself.  That is probably the conventional view.  I tend to think that this is the most probable reason.

Secondly the expansion of space is such that the elements composing the permeability vary in a way that compensates to keep the velocity of light constant.

Finally one for the wilder thinkers.  Because our models of physical laws expect the speed of light to be absolutely constant we interpret our observations assuming that it is.  However there could be alternative interpretations of the results of experiments that could allow the speed of light to vary slightly with time. For example: when the univere was more dense the speed of light might have been faster so the universe was effectively a bit larger than we think.  this could be quite interesting when we get back to the start of the "big bang because that could mean that the universe does not shrink to an infinitesimally small starting point as some theoreticians like to suggest but started at some finite size with an almost infinite velocity of light.

 

another_someone

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Speculation on the value of c?
« Reply #6 on: 09/12/2007 14:21:42 »
I would add to the above, all interesting issues, the following:

Are we sure that space is expanding?

What we believe is that objects in space are getting further away, but what does that actually tell us about space?

If two boats are floating on a patch of water, if the boats separate, does that mean that the water between them has actually expanded, or just that the have placed more water between themselves?

If order for us to say that the water itself is expanding, we have to look not at the boats floating on the water, but the container in which the water is placed.  We know nothing about the container in which space exists (i.e. about the total space occupied by space).  We know about the size of the visible universe, and that is expanding because our horizons are expanding, not because the space contained therein must be expanding.

There is also the problem of scale.  To say that something is bigger than it was, we need an absolute scale to measure it against.  Can we prove are scales are constant over time - could it be that rather than the distance between the parts of the visible universe getting bigger, that it is our measuring scales that are getting smaller?
 

Offline Dick1038

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Speculation on the value of c?
« Reply #7 on: 09/12/2007 18:25:37 »
I'm about to finish Joao Magueijo's book, "Faster Than the Speed of Light". He postulates that c was much larger during the early epoch of the universe. It seems to me that the permeability of space would indeed be different in the early universe.

His speculation is a proposed replacement for inflation. There doesn't seem to be as much "arm waving" as in the theory of inflation.  I concede that inflation is the best thing we got going today.

He wrote that the inflationary period was loosely analogous to super-cooled water, in order to explain it to non-physicists such as I (I'm a retired EE who really wanted to be an astronomer as a youth, but who didn't want to stay up all night freezing my ass off on top of a mountain). With super-cooled water, it won't change to ice until something disturbs it.  So what was the disturbance that stopped the inflation? 
 

Offline Soul Surfer

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Speculation on the value of c?
« Reply #8 on: 09/12/2007 23:00:12 »
Supercooled water once started, stops freezing when the energy released by the crystallisation raises the temperature back to the freezing point.  so I presume that the energy release during the "expansion" would do a similar thing.
 

Offline lightarrow

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« Reply #9 on: 10/12/2007 01:35:06 »
I would add to the above, all interesting issues, the following:

Are we sure that space is expanding?
I don't know the answer, however I propose a comical explanation: the universe is rotating  :)
(This maybe could even explain "dark energy"  ;))
 

Offline Dick1038

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« Reply #10 on: 18/12/2007 00:38:23 »
lightarrow: Rotating with respect to what?  Since the universe is "everything" it can only rotate with respect to "nothing", therefore it isn't rotating.
 

another_someone

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Speculation on the value of c?
« Reply #11 on: 18/12/2007 02:40:36 »
lightarrow: Rotating with respect to what?  Since the universe is "everything" it can only rotate with respect to "nothing", therefore it isn't rotating.

I don't see that as a problem.

The problem rather is that rotation needs an axis upon which to rotate, and so there must be a centre the the universe (something contrary to current thinking).

We can demonstrate rotation without requiring an external reference by looking for a centrifugal force in the plane of rotation that does not exist in the direction perpendicular to the plain of rotation.  We should also find (assuming rigid body rotation - which is not inevitable) that centrifugal force increases as we move away from the centre.
« Last Edit: 18/12/2007 03:27:22 by another_someone »
 

Offline chrisdsn

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Speculation on the value of c?
« Reply #12 on: 22/12/2007 05:42:52 »
Answering the original question; not the digression: What Einstein
taught is (based on the supposition, and later verification, that the
speed of light was constant) is that while space and time are different
things, they are made of the same "stuff". The human brain easily
understands that the 3 space dimensions are equivalent (made
of the same stuff), as what is called forward-backwards; left-right;
up-down, depends on how the person in question is situated: lying
down, facing north or south etc...

Time and space have a similar, but not identical, relationship. The
weirdness of relativity tells us that depending on how fast something
is moving with respect to an observer how fast time is moving or how
long things are changes (mathematically similar to the way that what you
see to the left or right of you depends on weather you are facing
forwards or backwards). As mentioned previously, for such a relationship
to exist, time and should be considered as being made of the same
"stuff".  It makes sense, then, to measure them in the same units.
While space is usually measured in meters, and time in seconds
these are esentially random measurement methods. In particular, they
are units decided before people realized that time and space are
related.  The speed of light you quoted is just the conversion factor
between the units of time and space. Theoretical physicists actually
tend to work in what they call "natural units" in which time and space
are treated equally.

To -- apologies --  belabor the point: It's as if, for some reason,
history had decreed that we measure distances to the left of us
in inches and to the right of us in meters. This would leave us
with a fixed "speed of left to right", which would just be the conversion
factor from inches into meters. It wouldn't mean anything, except that
physic doesn't favour left or right.   
 

Offline Dick1038

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Speculation on the value of c?
« Reply #13 on: 22/12/2007 17:54:32 »
another_someone:  The universe has no center nor edges, so as I've been told. The rotation would have to be Earth centered in order for the expansion to appear uniform in every direction.

 

Offline Soul Surfer

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« Reply #14 on: 29/12/2007 12:15:00 »
You are all thinking about rotation in terms of rigid bodies which is clearly untrue because rigid bodies are quite a rare feature of our universe even though our life on earth tends to be dominated by them.

Most material in the universe is in the form of fluid bodies restrained by gravity and or electromagnetism.

Our solar system rotates.  The planets orbiting the sun have a net angular momentum around a particular axis.  the sun itself is rotating with a much smaller amount of angular momentum around a similar axis.

Back in the 19th century it was worked out how bodies restrained by gravity  would behave and the "virial theorem"  (Look this up if you want to find out more) explains how bodies collapsing under their mutual gravity will eventually stabilise according to the forces associated with their rotational angular momentum and "temperature" (particle energies)

To find out how loose knit things like star clusters galaxies and the universe itself you have to measure the relative velocities if a large number of typical elements and see if there is a net angular momentum.  This is relatively easy if you can see the whole of the body involved but could be very difficult if you can only see a tiny part of it as seems likely for the universe as a whole (assuming that there was an inflationary period in the early stages of the big bang)  because all you would see is a slight tendency for there to be a generalised flow in one direction which was a bit faster towards the "centre".  Any such flow is masked by the overall expansion and the large "random" velocities of the galaxies in their own right and in their orbits around their particular cluster centres which are generally many hundreds of kilometres per second.

The cosmic microwave background could also contain information like this and this is what is meant by the somewhat unnecessarily dramatically named feature "the axis of evil" which appears in current observations.
 

another_someone

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Speculation on the value of c?
« Reply #15 on: 29/12/2007 13:22:28 »
another_someone:  The universe has no center nor edges, so as I've been told. The rotation would have to be Earth centered in order for the expansion to appear uniform in every direction.



I do totally agree that the axis of rotation would have to be Earth centred in order for the appearance of uniform expansion, and thus if we have a rotation that is not Earth centred, we should see a non-uniform expansion (even if the rotation is Earth centred, the expansion would only be uniform in one plane).  I was not suggesting that such a rotation could exist unobserved, but quite the contrary, that it should have a manifestation that we can test.
 

another_someone

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Speculation on the value of c?
« Reply #16 on: 29/12/2007 13:28:59 »
You are all thinking about rotation in terms of rigid bodies

No, I don't think I am making any such assumption.

All I was assuming is that for rotation to exist, matter must be travelling in a curved trajectory that is centred upon some focal axis, and in order for this to be the case there must be some centripetal force that maintains that curved trajectory, and that centripetal force is balanced by the acceleration of the trajectory (the centrifugal force), which should be acting only in the plane of rotation.  We should thus be seeing a difference between the centripetal force that is counterbalanced by the acceleration in the plane of rotation and the centripetal force that is not counterbalanced in the other planes.

None of this assumes that anything is rigid, only that there remains throughout the system some asymmetry of forces between the plane of rotation and other planes through which no rotation is occurring.
 

Offline McQueen

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Speculation on the value of c?
« Reply #17 on: 30/12/2007 13:32:50 »
Quote
A photon released from a star in a galaxy that was say 10 billion light years away from us 10 billion years ago would take more than 10 billions years to reach us because the space in between us and the star would have dramatically increased over 10 billion years especialy as recession velocities can exceed c.
Is this a trick answer,or is there something more to it, or do you state as a bald fact that whole galaxies can be travelling away from us at a speed faster than light?
« Last Edit: 30/12/2007 13:36:20 by McQueen »
 

Offline Dick1038

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« Reply #18 on: 04/01/2008 01:36:04 »
Angular velocity, like linear velocity, requires motion measured relative to some reference frame, e.g., inertial space.  But if inertial space is rotating, we can't measure it.
 

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Speculation on the value of c?
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