# The Naked Scientists Forum

### Author Topic: Constancy of the speed of light  (Read 14473 times)

#### DoctorBeaver

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##### Re: Constancy of the speed of light
« Reply #25 on: 17/12/2005 14:30:06 »
quote:
Alternatively I tend to prefer to see it as evidence that some sort of evolutionary process has already taken place as the physical laws "settled down" during the initial stages of the big bang. This process maximises the complexity and longevity of any universe as it is formed.

That's more-or-less what I was saying, although I wouldn't use the word "evidence". We can only reverse-engineer the universe according to our current understanding of the laws that govern the way it is today (or as far back in time as we can see); and there are some fairly large holes in that knowledge anyway. Take inflation theory. That may help to explain 1 question but it raises other questions that we can't answer.
With doubt now being cast upon the absoluteness of the fine structure constant, there may well be a case to be made for other universal constants not always having had the values they have now.

#### Searcher

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##### Re: Constancy of the speed of light
« Reply #26 on: 28/12/2005 22:40:34 »

quote:
can anyone tell me what hard evidence we have for the constancy of the speed of light? (i.e. evidence that different people/instruments will always measure c - in a vacuum - to be the same speed, irrespective of their motion relative to the source.)

But is there any further experimental evidence or theoretical reasons why c must be constant? Any help would be much appreciated. Many thanks.

I have a theory on this subject and it goes like this:-

Back to basics, velocity = distance travelled / time taken.

Assume the distance is a fixed amount say 300,000 Km therefore 300,000Km /sec = speed of light.

If the velocity changes then time changes. But what if time cannot be changed then the velocity is fixed.

My theory is that at the big bang time was the first thing to come into existence since I have not heard of any matter existing outside time. Time then moved out and created the space for the cosmos to expand into. Therefore time itself must have a velocity and since nothing can exist in front of time nothing can travel faster than time moving out creating space.  It follows that time is moving out at the speed of light hence nothing can travel faster.

I am preparing a paper on the subject at the moment and would welcome any help or criticism. The mathematics is quite daunting.

#### Soul Surfer

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##### Re: Constancy of the speed of light
« Reply #27 on: 29/12/2005 10:18:02 »
Thought Albert Einstin sorted that out quite adequately a century ago.

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#### DocN

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##### Re: Constancy of the speed of light
« Reply #28 on: 29/12/2005 21:43:02 »
I have read that this early time dimension could be "space-like"--that is, giving us four space-like dimensions at the big bang--with no time element present at this event.  I wonder what event set off the formation of such a construct?  I know it's difficult enough to understand the instant and short period after  the big bang but even more interesting is what was happening before it.
DocN

#### another_someone

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##### Re: Constancy of the speed of light
« Reply #29 on: 29/12/2005 22:44:03 »
OK, I am about to demonstrate my total ignorance in these matters (as if I had not amply demonstrated sufficiently already).

I understand (or at least, have been able to look up – which is probably well short of claiming to understand) that the difference between spacelike and timelike relate to Minkowski space.

First problem is that although at a very superficial level I can understand what a matrix is, but understanding the nomenclature of matrix manipulations is beyond me.

Maybe if I could get over that hurdle, I could understand what the rest of this was about, but can someone explain to be in experiencial terms what would be the effect of a universe with 4 spacelike dimensions.

To my tiny mind, time is simply the way we measure change.  If we have no time, then how would something be able to change, so how could you change from a situation without time to one with time if there was no time over which things changed?

Sorry if this is getting seriously naïve, but I am seriously getting to the point where I feel I have to put my hands up and surrender.

Ofcourse, maybe the answer you will come back with is that it will take a 3 year degree course to explain it all, and we don't have 3 years to do it in.

#### Soul Surfer

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##### Re: Constancy of the speed of light
« Reply #30 on: 29/12/2005 23:23:19 »
You should read the book "the end of time" by Julian Barbour a respected cosmologist who explains a lot of quantum wierdness by suggesting that we should think of a timeless universe in which all the possible sequential configurations occur at all times and our observation creats a set of world lines witihn this much vaster universe of quantum potential.  It is quite readable and does not make very great mathematical demands on the reader

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#### another_someone

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##### Re: Constancy of the speed of light
« Reply #31 on: 30/12/2005 01:02:44 »
quote:
Originally posted by Soul Surfer

You should read the book "the end of time" by Julian Barbour a respected cosmologist who explains a lot of quantum wierdness by suggesting that we should think of a timeless universe in which all the possible sequential configurations occur at all times and our observation creats a set of world lines witihn this much vaster universe of quantum potential.  It is quite readable and does not make very great mathematical demands on the reader

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OK, book on order from Amazon – I'll see if it makes the difference.  Some of the reviews seem a bit mixed, although they seem to indicate more that they disagree with the conclusions of the author, but nonetheless seemed to be a good way of clarifying a number of concepts along the way.

I should probably also find myself a simple book on understanding matrix manipulation beyond simply multiplying matrices (which is as far as my comprehension presently goes).

#### realmswalker

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##### Re: Constancy of the speed of light
« Reply #32 on: 30/12/2005 01:28:43 »
what if the speed of light is relative to the time of the universe...
the universe is expanding, so is it possible to say that the time that it takes a beam of light to travel across the universe is the constant, not the speed its self. just a notion

#### Soul Surfer

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##### Re: Constancy of the speed of light
« Reply #33 on: 30/12/2005 11:21:11 »
This cannot be true because observations of remote objects clearly indicate that the speed of light a long time ago wa exactly the same within many decimal places what it is today.  Even variable speed of light models only allow tiny changes within the easily observable universe

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#### Soul Surfer

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##### Re: Constancy of the speed of light
« Reply #34 on: 30/12/2005 11:26:39 »
I have already mentioned Roger Penrose's "Road to Reality" elsewhere on this forum.  This starts with an assumption of very little mathematical knowledge and takes you all the way to quantum gravuty and string theory including tensor calculus etc.  It's the best and most readable maths book that I know.

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#### another_someone

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##### Re: Constancy of the speed of light
« Reply #35 on: 30/12/2005 14:44:41 »
quote:
Originally posted by Soul Surfer

I have already mentioned Roger Penrose's "Road to Reality" elsewhere on this forum.  This starts with an assumption of very little mathematical knowledge and takes you all the way to quantum gravuty and string theory including tensor calculus etc.  It's the best and most readable maths book that I know.

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Curiously enough, Amazon claim that is not yet published – due out in February.

#### Soul Surfer

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##### Re: Constancy of the speed of light
« Reply #36 on: 30/12/2005 20:35:05 »
That's probably the paperback version I bought the hardback earlyish 2005 shortly after it was published. and spent a lot of the summer reading it.

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#### The Naked Scientists Forum

##### Re: Constancy of the speed of light
« Reply #36 on: 30/12/2005 20:35:05 »