Speed of Light and the Big Bang

[Jesus]

Ok, I have a question that I hope makes sense, and have been unable to answer on my own. I consider my knowledge of general science to be a bit above average (not saying much considering the average American's grip of the subject) but I recently came across something that is more than a bit perplexing. Perhaps I am not understanding it well enough, or perhaps my information is incomplete or wrong. I am certain the folks here can help.

I was reading a book this evening at my local Borders (I can't recall the author or title, sadly enough. I was there to buy another book, but this one caught my eye), and in it is a description of the Big Bang. It goes into some detail regarding the expansion of the early universe and how, within only a matter of minutes, it grew to vast sizes.

Now, the rates listed in this book are off the charts, and certainly faster than the speed of light (the author described millions of miles in only a few seconds). My first question is, are these rates accurate?

If so, how can this be? I thought that the speed of light was, as Carl Sagan described it, the "universal speed limit". Nothing can go faster, in theory. But, if universe was expanding after the Big Bang at the speed described, things were moving a lot faster than light. How can this be?

Thanks in advance for any insight into this.

[Beleth]

The rate of expansion of the universe - the speed of space, if you will - is not constrained by the speed of light.

This is a difficult concept. There was an excellent article in the March 2005 Scientific American (http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009F0CA-C523-1213-852383414B7F0147) about it.

[espritch]

The theory of very rapid expansion of the universe in the early moments of the big bang is called Inflation. It is posited mainly, IIRC, to explain large scale structure of the universe as being a result of quantum fluctuations in the early universe when it was very compact (no, I don't really understand that either).

As to the question of how this expansion could have exceeded the speed of light, I think that has to do with what that expansion actually represents. It wasn't that matter and energy in the universe were moving rapidly, it was that the universe itself (i.e. space time) was expanding rapidly. The rules that apply to objects and energy moving through space time don't necessarily apply to space time itself.

Even today, distant objects in our universe are moving away from us at speeds greater than the speed of light. This is not due to any absolute inertial motion of the objects themselves (and so does not violate the C limit), but rather due to the expansion of space between the objects and ourselves.

Does that help? If not, you'll have to wait for a reply from someone with a better handle on this stuff than me.

[AmateurScientist]

Yeah, what they said. Doesn't violate the speed limit at all. Very good question, though.

AS

[SezMe]

Originally posted by espritch
Even today, distant objects in our universe are moving away from us at speeds greater than the speed of light.
That is a new one for me. Can you give me a site where I could read more?

[espritch]

From this link: http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0011070

Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D=c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally. .

[SezMe]

Thanks, espritch. My mate just reminded me that we heard all about this at a lecture by Alex Fillipinko (sp?), an astronomer we know who is into dark matter, dark energy, and the like.

I guess my grey matter is getting too grey. :( :)

[Dr. Fendetestas]

From the very interesting Ned Wright's Cosmology Tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm):

Can objects move away from us faster than the speed of light?

Again, this is a question that depends on which of the many distance definitions one uses. However, if we assume that the distance of an object at time t is the distance from our position at time t to the object's position at time t measured by a set of observers moving with the expansion of the Universe, and all making their observations when they see the Universe as having age t, then the velocity (change in D per change in t) can definitely be larger than the speed of light. This is not a contradiction of special relativity because this distance is not the same as the spatial distance used in SR, and the age of the Universe is not the same as the time used in SR. In the special case of the empty Universe, where one can show the model in both special relativistic and cosmological coordinates, the velocity defined by change in cosmological distance per unit cosmic time is given by v = c ln(1+z), where z is the redshift, which clearly goes to infinity as the redshift goes to infinity, and is larger than c for z > 1.718. For the critical density Universe, this velocity is given by v = 2c[1-(1+z)-0.5] which is larger than c for z > 3 .
For the concordance model based on CMB data and the acceleration of the expansion measured using supernovae, a flat Universe with OmegaM = 0.27, the velocity is greater than c for z > 1.407.


I'm afraid this quote may be confusing if you don't read at least part of the Tutorial, but here it is anyway. If you are interested, take a look at the section about the many distances (http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD). If after reading a bit of this (I know it can be overwhelming), you still have some doubts, feel free to ask again here.

[epepke]

Originally posted by Beleth
The rate of expansion of the universe - the speed of space, if you will - is not constrained by the speed of light.

This is a difficult concept. There was an excellent article in the March 2005 Scientific American (http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009F0CA-C523-1213-852383414B7F0147) about it.

Thanks for posting this link. I read the article, and it inspired me to start a thread on another forum about some things I've been thinking about for a decade or so. If you're interested, it's here: http://www.iidb.org/vbb/showthread.php?t=135150

[Jesus]

These explanations have been very helpful. I make a loose parallel between that and objects moving on the Earth. Let's say I can only run at a top speed of 20 mph (which I can't, but let's just say), but I'm really moving at 1000 mph with the revolution of the Earth around the Sun.

It's not a great analogy, I guess, but the 20 mph is the speed of light while the Earth's speed is the rate of expansion of the universe.

In any event, I have some reading to do!

[Dr Adequate]

Originally posted by Jesus
These explanations have been very helpful. I make a loose parallel between that and objects moving on the Earth. Let's say I can only run at a top speed of 20 mph (which I can't, but let's just say), but I'm really moving at 1000 mph with the revolution of the Earth around the Sun. Imagine ants crawling on the surface of a ballon being inflated, where the ants represent light, the speed of ants represents the speed of light, and the surface of the balloon represents space.

[Soapy Sam]

The balloon is in an airliner flying due west along the equator at 400mph (groundspeed) and 33,000 feet. Cabin pressure is equivalent to 12000 ft altitude.
1. How long to empty the bath?
2. How much larger is the balloon than it was on the ground?
3. Allowing for Lorentz- Fitzgerald contraction, how much larger?

Kidding aside- what if c has varied with time? Everything else slows down as it gets older- why not c ?

[espritch]

Kidding aside- what if c has varied with time? Everything else slows down as it gets older- why not c ?

According to the theory of relativity, time is relative. The faster a thing is moving, the slower it ages. A photon moving along at C doesn't age at all. And since it isn't getting older, why would it slow down?

[lifegazer]

"Even today, distant objects in our universe are moving away from us at speeds greater than the speed of light. This is not due to any absolute inertial motion of the objects themselves (and so does not violate the C limit), but rather due to the expansion of space between the objects and ourselves."

Does somebody have an explanation/link explaining why/how, if the above is true, we can still see those distant objects?
It seems to me that if the space between myself and an object is expanding faster than the speed of light, that the object should be unobservable, since the light travelling from that object would actually be further away from me with each passing second.

[Dr. Fendetestas]

Originally posted by lifegazer
"Even today, distant objects in our universe are moving away from us at speeds greater than the speed of light. This is not due to any absolute inertial motion of the objects themselves (and so does not violate the C limit), but rather due to the expansion of space between the objects and ourselves."

Does somebody have an explanation/link explaining why/how, if the above is true, we can still see those distant objects?
It seems to me that if the space between myself and an object is expanding faster than the speed of light, that the object should be unobservable, since the light travelling from that object would actually be further away from me with each passing second.

Check the cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmo_02.htm) I linked earlier. In short, the definition of distance is not the same as in Special Relativity (so nothing really moves faster than light).

[lifegazer]

Originally posted by Dr. Fendetestas
Check the cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmo_02.htm) I linked earlier. In short, the definition of distance is not the same as in Special Relativity (so nothing really moves faster than light).
Are you saying that - contrary to earlier statements - spacetime does not expand faster than the speed of light?
If not, then I still need an answer to my previous question.

[Dr. Fendetestas]

Originally posted by lifegazer
Are you saying that - contrary to earlier statements - spacetime does not expand faster than the speed of light?
If not, then I still need an answer to my previous question.

Eeeh... Spacetime doesn't expand, space does.

That aside, but you must keep in mind is that in Physics one often encounters things called 'speed', which are greater than c. This does not contradict SR, because each and every time such a 'speed' appears, no information or energy is being transferred, so you might say that it isn't a 'real' speed.

The question of the 'speed' of the expansion is complex, because one must be very careful with the definition of 'distance' and the definition of 'time' employed. All of these are covered in the tutorial and the FAQ (http://www.astro.ucla.edu/~wright/cosmology_faq.html).

A typical example of the difficulties: 'We say that the Universe was concentrated at the time of the Big Bang, yet we currently think it is infinite. How can something grow to an infinite size in a finite time?' The answer is, of course, that it can't, actually the only thing that was concentrated in the BB was the visible universe (http://www.astro.ucla.edu/~wright/infpoint.html), the whole Universe would be infinite even then.

But even the visible Universe is bigger than c*(age_of_the_universe). For example, we can see an object 30 billion light years away when the universe is 10 billion years old. This is because the 30 billion light years are the separation now, the difference in space coordinates for two objects at the same time. This is bigger than c times the light travel time because the Universe has grown in the meantime.

In short:


If we assume that the distance of an object at time t is the distance from our position at time t to the object's position at time t measured by a set of observers moving with the expansion of the Universe, and all making their observations when they see the Universe as having age t, then the velocity (change in D per change in t) can definitely be larger than the speed of light. This is not a contradiction of special relativity because this distance is not the same as the spatial distance used in SR, and the age of the Universe is not the same as the time used in SR.


All this probably does not make things any clearer for you, but I don't really know where to start. If you want a more detailed explanation, why don't you make a post summarising what you know about cosmology? Just one or two short paragraphs saying what you think the Big Bang Theory says. I'm saying this because very often this model is misunderstood at a deeper level, so trying to explain this apparent superluminal velocities may do more damage than good.

[epepke]

Originally posted by lifegazer
Does somebody have an explanation/link explaining why/how, if the above is true, we can still see those distant objects?

The idea is that, when the light left, there was less distance. The total distance that the light has traveled is less than the current distance, because space has been expanding behind the light. Also in front of it, but the light still gets there.

[jmercer]

Regarding lightspeed... (http://www.news.harvard.edu/gazette/1999/02.18/light.html) and how about lightstopping? :) (http://www.msnbc.com/news/242698.asp?cp1=1)

[Soapy Sam]

Originally posted by espritch
According to the theory of relativity, time is relative. The faster a thing is moving, the slower it ages. A photon moving along at C doesn't age at all. And since it isn't getting older, why would it slow down?

It wouldn't. It would still be travelling at the speed of light,
which would be as fast as it was possible to go. But the speed of light would be lower than it used to be. Perhaps the fundamental unit of time is getting shorter?

[luvhumility]

I "feel" there is an energy form that may travel faster than the speed of light.
This energy form would need to be of a type that could transcend matter by passing directly through it. Visible light cannot do this. Some high energy particles do, but only at given distances. This energy form would need to be comprised of varying frequency's, velocities, polarizations and amplitudes that would allow it to pass directly through the matter it interacts with. Even solid objects would be transparent to it… It seems this could be possible. If it is happening now, my question is how would we detect or measure it? I think it may also possibly be able to cause expansion or dilation of matter itself. C, I doubt is the max anything can travel at. There is so much more to learn. I would not be surprised if very soon, a physical development will blow the C photon train speed out of the water.

lh