The Nature of Light

[Neil T]

I am coming at this as an interested layman and quite a lot of the mathematics is beyond my abilities, but I do read an awful lot and am aware of most of the general principles, so please be gentle.

 

Relevant General principles:

There is nothing about local space or time that is unique or special.

The speed of light is not about light but is more accurately thought of as the speed of causality or something similar.

Odd facts

The furthest in time our telescopes can see in time is almost to the "big bang" and prevented from seeing further by the cosmic background radiation.
That corresponds with the furthest in distance our telescopes can see because of the red-shift of distant objects approaching infinity.

That makes me think:

We seem to be in a very interesting and specific point in time in which in which we can see almost exactly to the big bang.

 

Is it plausible that we're measuring the speed of light wrong?

Is it possible that it should be measured, not in "miles per hour" or similar but as a constant fraction of the size of the universe?

Is it possible that the speed of light is such that it would always reach the limit of the universe in the life of the universe?

 

This should be easy to test but might require finer instruments than we have available but if this were true the speed of light should be increasing very, very slightly (as measured in miles/hour) proportional to the total size change of the visible universe.

 

I've tried to imagine this in four dimensions (which is admittedly very hard) but I think it would mean that everybody in the universe could see exactly back to the big bang (assuming mw bg not in the way) with red shift approaching infinity at that point.

 

A big thank you to anyone who takes this seriously.

 

 

[Endy0816]

You've got things confused a bit.

 

The early Universe was opaque to light, cosmic microwave background radiation is from when that stopped being the case.

[Mordred]

The CMB at z=1104 roughly is nowhere near infinitely redshifted. The dark ages prior to the surface of last scattering is due to the particles that form our atoms not being bound to atoms. Ie electrons, protons neutrons. This means that the mean free path of photons travelling through this environment is too short. The photons collide and scatter with other particles.

 

When the temperature drops sufficiently enough that atoms can form with potential stability then the mean free path of photons increases to what it is today

[John Cuthber]

 

We seem to be in a very interesting and specific point in time in which in which we can see almost exactly to the big bang.

 

 

That's true (as far as we know) for almost any point in the universe.

[Strange]

That's true (as far as we know) for almost any point in the universe.

And any time.

[Neil T]

You've got things confused a bit.

 

The early Universe was opaque to light, cosmic microwave background radiation is from when that stopped being the case.

 

I left that out because I didn't think it was relevant.Why do you think it is?

The CMB at z=1104 roughly is nowhere near infinitely redshifted. The dark ages prior to the surface of last scattering is due to the particles that form our atoms not being bound to atoms. Ie electrons, protons neutrons. This means that the mean free path of photons travelling through this environment is too short. The photons collide and scatter with other particles.

 

When the temperature drops sufficiently enough that atoms can form with potential stability then the mean free path of photons increases to what it is today

I'm not sure what all you're trying to tell me but I've read several times that at the rate the universe is expanding the furthest reaches of what we can currently see will soon be lost to us because they will be receding faster than light. That was accompanied by a longish explanation of how that's possible which sounded like nonsense to me and was a part of what led me down this line of thought.

 

But if the furthest reaches of the universe are receding at a speed which "will soon make them invisible to us when they are receding beyond light speed" I take that to mean that they are currently close to it, more or less. I've seen some graphs of red shifts which look at first sight like the furthest visible objects might be about the same proportion of the way to being infinite as the CMB is between us and the big bang.

That's true (as far as we know) for almost any point in the universe.

 

This is sort of what I was saying but the context makes me suspect there is a misunderstanding involved.

 

I have read several times from respected (although populist) physicians that the expansion of the universe will "soon" make the outer limits of it invisible because light from those stars can never reach us.That sounds to me like "infinitely red shifted".

 

But the distance we can see (almost to where light can never get to us) seems to roughly correspond to the distance in time we can see (almost to the big bang). I'm suggesting that maybe that's always true for every point in the universe because that's how the speed of light works.

 

Your suggestion that it's true for any point in the universe makes sense now, but doesn't that make this moment in time special? Isn't that an assumption we ere enjoined to avoid?

 

[Mordred]

actually the time when light can no longer reach us due to expansion isn't for several billion years in the future. However that hasn't anything to do with the CMB opacity.

 

Assuming my back of the envelope calculations is correct and nothing changes from the Planck dataset roughly when the universe is 17.8 billion years old.

Edited November 18, 2016 by Mordred

[Neil T]

And any time.

How can it be true for any point and any time and still be static speed in conventional terms? Like miles/hour?

 

And if its at "any time" how does a place carry on seeing the light it's already seen?

[Strange]

How can it be true for any point and any time and still be static speed in conventional terms? Like miles/hour?

 

And if its at "any time" how does a place carry on seeing the light it's already seen?

 

 

I assumed you were talking about the cosmic microwave background (but maybe you weren't).

 

But what I said isn;'t really true. Eventually it will become so red-shifted (and faint) that it is no longer detectable.

 

I would defer to Mordred on this subject...

I'm not sure what all you're trying to tell me but I've read several times that at the rate the universe is expanding the furthest reaches of what we can currently see will soon be lost to us because they will be receding faster than light. That was accompanied by a longish explanation of how that's possible which sounded like nonsense to me and was a part of what led me down this line of thought.

 

Interestingly, we can see things that are receding faster than light. The reason things move outside the observable universe is because expansion carries the light away faster than it moves towards us.

[Mordred]

How can it be true for any point and any time and still be static speed in conventional terms? Like miles/hour?

 

And if its at "any time" how does a place carry on seeing the light it's already seen?

I'm not really sure I understand this the way its worded.

[Neil T]

actually the time when light can no longer reach us due to expansion isn't for several billion years in the future. However that hasn't anything to do with the CMB opacity.

I was under the impression it was sooner than that, which might invalidate my hypothesis (though possibly not) but you seem to be misunderstanding my references to CMB.

 

First though... if this is the case then we can potentially see (via the speed of light) quite a lotmore of the universe than actually exists. The CMB and time limits prevent seeing out that far I know but that doesn't seem to jibe with what others here are saying. Let me see if I got this straight...

 

Per your envelope: the speed of light and rate of expansion currently allows us to see about 17 billion light years of universe but we can only actually see about 14 billion light years of universe because the universe is only about 14 billion years old. That doesn't fit with my idea terribly well, but it also doesn't seem to match up with what others are saying in this thread.

 

And it also doesn't match with what I took a decade convincing myself of about light, that it travels at the same speed for both pitcher and catcher regardless of their relative velocities.

 

But even given your numbers, we are traveling away from the furthest galaxies at circa 3/4 the speed of light (or vice versa). I don't know how to factor time dilation into those calculations but it seems like it should be a factor. It also seems like time dilation could account for the difference between 14 and 17 billion years making my original hypothesis viable again.

 

For that matter, when people talk about how far away distant galaxies "are" I've never heard them be specific about when they're actually talking about or make any mention of how time dilation plays into that. That's a bit off topic though so only respond if it's relevant and/or simple to explain.

[Mordred]

Well I first off you need to understand how cosmological redshift and expansion works with regards to how far light can transverse. Think of it this way the speed of light is far faster than the localized rate of expansion. Which is roughly 70 km/s/Mpc.

 

This article will save some time there.

 

http://tangentspace.info/docs/horizon.pdf :Inflation and the Cosmological Horizon by Brian Powell

 

its based on this article.

 

http://arxiv.org/abs/astro-ph/0310808 :"Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe.

 

Time dilation isn't involved when it comes to expansion this is where cosmological redshift differs from gravitational redshift.

 

Expansion causes a volume change at any time slice such as now. A homogeneous and isotropic fluid has at sufficient size scales roughly 100 Mpc a uniform mass density throughout the universe at any particular moment in time.

 

So you get time dilation/length contraction thats a common misconception.

 

Assuming we had a different means of seeing beyond the opacity of the dark ages. Ie measuring reliably the neutrino background we could see much further back till roughly when neutrinos drop of thermal equilibrium and decouples.

 

This would be roughly 10^-12 seconds after BB. Though we don't have this technology yet.

 

Here is a chronology of the BB.

 

https://en.m.wikipedia.org/wiki/Chronology_of_the_universe

 

it details the dark ages.

Edited November 18, 2016 by Mordred

[Neil T]

 

 

I assumed you were talking about the cosmic microwave background (but maybe you weren't).

 

But what I said isn;'t really true. Eventually it will become so red-shifted (and faint) that it is no longer detectable.

I referred to CMW merely as an identifiable marker point in the history of the universe which we can't see beyond in either time or distance but which we can and do estimate to be a specific time and distance away from which we extrapolate the age and size of the universe.

 

"so red-shifted (and faint) that it is no longer detectable" is the red shift approaches infinity I referred to.

[michel123456]

And any time.

That is not the opinion of L. Krauss

 

FLATOW: 1-800-989-8255. You mentioned in your book that we are lucky to be living in this time in the universe.

 

KRAUSS: Yeah, I mean for a variety of reasons. One is in the far future, and by the far future I mean hundreds of billions of years, astronomers and radio hosts on planets around other stars will look out at the universe, and what they'll see is the universe we thought we lived in 100 years ago, all of the other galaxies will have disappeared expect for our own, and people will assume, or beings will assume, they live in a universe that's basically infinite, dark and empty except for one galaxy, with no evidence of the Big Bang.

 

from http://www.npr.org/2012/01/13/145175263/lawrence-krauss-on-a-universe-from-nothing

[StringJunky]

That is not the opinion of L. Krauss

 

from http://www.npr.org/2012/01/13/145175263/lawrence-krauss-on-a-universe-from-nothing

I remember that: Martin, the cosmology expert, posted here it a few years ago

Edited November 20, 2016 by StringJunky

[Mordred]

Yes but Krauss failed to mention that unique point on time is several billion years long.

[michel123456]

Yes but Krauss failed to mention that unique point on time is several billion years long.

Anyway, that makes a bizarre feeling. That of being at a very definite and special place in time. That constitutes another difference between Space and Time. We are lost in space in this Universe, but not lost in time. Because in time our position is well defined. Following Krauss.