Thread: Expansion of Space and Age of the Universe

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Expansion of Space and Age of the Universe

I have seen on several shows that we know how old the universe is by the rate of expansion of the universe as we know it now. My question is how do we know this rate of expansion, as well, if we dont know how far the inflation of the universe took space, how do we know the age? I dont know , I think I confused myself here more than anything, trying to write this question lol

2. Originally Posted by pkarnes
I have seen on several shows that we know how old the universe is by the rate of expansion of the universe as we know it now. My question is how do we know this rate of expansion, as well, if we dont know how far the inflation of the universe took space, how do we know the age? I dont know , I think I confused myself here more than anything, trying to write this question lol
Wikipedia has an article on the age of the universe here:

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

The article contains a more comprehensive answer to your question than I could possibly hope to provide you in my own words.

Here is a short excerpt from that article that applies to your specific question about how we get the age of the universe from the rate of expansion:
The problem of determining the age of the universe is closely tied to the problem of determining the values of the cosmological parameters. Today this is largely carried out in the context of the ΛCDM model, where the Universe is assumed to contain normal (baryonic) matter, cold dark matter, radiation (including both photons and neutrinos), and a cosmological constant. The fractional contribution of each to the current energy density of the Universe is given by the density parameters Ωm, Ωr, and ΩΛ. The full ΛCDM model is described by a number of other parameters, but for the purpose of computing its age these three, along with the Hubble parameter H0 are the most important.

If one has accurate measurements of these parameters, then the age of the universe can be determined by using the Friedmann equation. This equation relates the rate of change in the scale factor a(t) to the matter content of the Universe. Turning this relation around, we can calculate the change in time per change in scale factor and thus calculate the total age of the universe by integrating this formula.
Chris

3. Imagine you wake up in the middle of a flat desert and you see that your pet turtle is gone, but its tracks lead directly away from you and, with binoculars, you see it 1 mile away from you. You happen to know your turtle moves at a constant speed of 1/2 miph. Thus, you now kinow that it left your camp 2 hours earlier.

Once astronomers were able to produce reasonably accurate distances to other galaxes, then their other discovery of how to determine how fast they are traveling away from us allowed them to calculate when we were, essentially, all together at one tiny spot.

It's not quite that simple, but that is the basics to it.

It was the discovery that certain variable stars (Cepheids) produce known values of brightness based on on fast they go from bright to dim. This allowed them to determine the distance to the nearer galaxies. Refinements came when they discovered that a certain type of supernova (Type Ia) was another "standard candle", which extended their distance measurements greatly -- billions of light years.

That, alone, only provides the distance. The rate of travel away from us for these galaxies became known by determining the redshift of light. It is similar to Doppler used on police radar. Wavelengths change when the source of light, or sound, comes from an object moving toward or away from the observer.

Many other techniques combine to confirm the accuracy of their other measurements. The result provides extremely strong arguments for an expanding universe. I think it was around 1995 when they, surprisingly, discovered that the expansion rate is now getting faster and faster, slightly.

Since this is your first post, it is a little hard to tell how fast to throw the balls to you. I hope this helps.
Last edited by George; 2011-May-14 at 04:13 PM. Reason: 2 gramms

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I believe the question may be how Inflation would affect the
calculated age. For a few minutes I thought I could answer
that, but then discovered that I can't.

-- Jeff, in Minneapolis

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I have read of certain groups of astrobiologists who tend to estimate that "early forms of life" on Earth existed up to 750,000,000 years prior to the current "accepted" numbers and there if one were to "attempt" to "plug" in the numbers the age of the universe is about 1 billion years younger (than the accepted number). Although it sounds controversial---(I am throwing out this as food for thought, only!)

I am currently searching for the reference----

6. An absolute statement, describing the age of anything (including the universe) in terms of a relative parameter such as time (or space) is by definition flawed.

7. Originally Posted by a1call
An absolute statement, describing the age of anything (including the universe) in terms of a relative parameter such as time (or space) is by definition flawed.
I think the questions asked in the OP were: "...My question is how do we know this rate of expansion, as well, if we dont know how far the inflation of the universe took space, how do we know the age?..."

I really don't think that pkarnes in interested in opening a debate about the philosophical meaning of "time" or "age".

Chris

8. Originally Posted by John Jaksich
I have read of certain groups of astrobiologists who tend to estimate that "early forms of life" on Earth existed up to 750,000,000 years prior to the current "accepted" numbers and there if one were to "attempt" to "plug" in the numbers the age of the universe is about 1 billion years younger (than the accepted number). Although it sounds controversial---(I am throwing out this as food for thought, only!)

I am currently searching for the reference----
references? So we can put what is being said into context?

9. Originally Posted by csmyth3025
I think the questions asked in the OP were: "...My question is how do we know this rate of expansion, as well, if we dont know how far the inflation of the universe took space, how do we know the age?..."

I really don't think that pkarnes in interested in opening a debate about the philosophical meaning of "time" or "age".

Chris
Hi csmyth3025,
I was not being philosophical. Relativity of time with respect to speed, space, and depth of the gravitational field all factor in determining the age of the universe. Keep in mind that the measure of time moments after the BB must take into account the immense density of space which has been very gradually being reduced due to expansion of space ever since. if we could somehow observe the evolution of the universe say "half-way since BB", say by observing a distant super nova, what conclusion can we reach knowing that at the "time" the density-of-space, was greater than it is now? What does that tell you about the "half-way since BB"?
ETA: How would the phrase "1 second after the BB" mean differently if it was measured now (after the fact, by remote observation), compared to a hypothetical clock present at the time?
ETA-II: How many femto-seconds would a clock falling into a black hole and at the EH register in 13 billion years?
Last edited by a1call; 2011-May-15 at 03:07 AM.

10. Watch this series of lectures by Susskind. It explains the FLRW equations (Friedman above) which come from general relativity. It requires some understanding of calculus, IIRC.

11. Originally Posted by a1call
Hi csmyth3025,
I was not being philosophical. Relativity of time with respect to speed, space, and depth of the gravitational field all factor in determining the age of the universe. Keep in mind that the measure of time moments after the BB must take into account the immense density of space which has been very gradually being reduced due to expansion of space ever since. if we could somehow observe the evolution of the universe say "half-way since BB", say by observing a distant super nova, what conclusion can we reach knowing that at the "time" the density-of-space, was greater than it is now? What does that tell you about the "half-way since BB"?
ETA: How would the phrase "1 second after the BB" mean differently if it was measured now (after the fact, by remote observation), compared to a hypothetical clock present at the time?
ETA-II: How many femto-seconds would a clock falling into a black hole and at the EH register in 13 billion years?
Problem with that view is there is no external observer. Everyone's proper time would have been the same. Saying that time progresses slower in the early universe doesn't mean anything because it progressed slower for every part of the universe. IE if you could take a bunch of cesium atoms and sprinkle them through out the universe and count the number of oscillations each on has had since the big bang then they'd all be roughly the same minus any that ended up very close to a black hole for some period of time.

1sec in the early big bang was 1sec. In a way time more was more uniform in the very universe because the energy density was more uniform. Unless you propose some mechanism to step outside of the universe to compare times...but then if you step out of space time to compare times does it even make sense?

12. Originally Posted by WayneFrancis
minus any that ended up very close to a black hole for some period of time.
Hi WayneFrancis,
How could any end up any distance away from all black holes in the universe in the early universe?
The difference in the density of the early universe is only one factor influencing the clocks. There is also the more familiar relativity of time with respect to inertial frames. Any absolute statement can be objected to at infinite other frames.

Plus, no stepping out mechanism needs to be proposed. We have effectively stepped out of the early universe by spatial expansion. Any observations that we make, must take into account the fact that our clocks are ticking faster than any (virtual clocks such as supernovas) we observe directly in the past. In effect if we look back far enough, we should see these clocks stop ticking all together. If we don't, then there must be something fundamentally wrong with our universe (We all know our mainstream theories are written in stone, right? ).

13. Thanks WayneFrancis for your reply. I was going to respond to a1call's proposition in the same way - but you said it much better.

Actually, I posed the very same conjecture a long time ago in another thread elsewhere and got the same response.

Still, there remains a nagging question in my mind about whether one second in the early universe is comparable to one second as we perceive it today. The reason for this, of course, is that the gravitational field in the early universe was presumably much stronger back then as opposed to the gravity experienced by our earthbound clocks.

Although one second was undoubtably one second for "observers" in the early universe, we are, in a sense, now the outside observers viewing those early events in a distant and greatly reduced gravitational field. It's hard for me to reconcile the notion of the "faster" clocks on GPS satelites vs the "slower" ground-base clocks here on Earth (due to the stronger gravitational field) with the notion that big bang nucleosynthesis transpired over a period of about 17 minutes of "our" time.
(ref. http://en.wikipedia.org/wiki/Big_Ban...ucleosynthesis )

I think this question might be a good subject for a new thread (or, perhaps, another one has alredy been started on this subject - does anyone know?).

Chris

Edited to correct spelling errors

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Originally Posted by WayneFrancis
references? So we can put what is being said into context?
I don't have them handy at the moment---and I dearly apologize . . . . and I will continue to look.

I do have them in my possession but I am unable to find them!

Perhaps I will start a new thread when I find them?

15. Originally Posted by a1call
Hi WayneFrancis,
How could any end up any distance away from all black holes in the universe in the early universe?
I never qualified the black holes as being in the early universe, ie the first few hundred thousand years. But if you put a cesium atom next to a black hole from lets say even 1 billion years after the big bang then today brought any other average cesium atom back into contact with the one near the black hole then number of oscillations could vary greatly depending on how close the first one was to the black hole's event horizon.

In the early universe they'd all be ticking away at the same rate. IE you wouldn't have any position that would observe any of them ticking faster or slower by any significant amount.

Originally Posted by a1call
The difference in the density of the early universe is only one factor influencing the clocks. There is also the more familiar relativity of time with respect to inertial frames. Any absolute statement can be objected to at infinite other frames.
What? I'm not following. The early universe had very little curvature. Remember in GR curvature is brought about by differences in densities. Since there was very little difference in densities in the early universe we can consider the early universe, at least our visible portion of the universe, to have been in the same inertial frame and thus in the same frame of reference.

Originally Posted by a1call
Plus, no stepping out mechanism needs to be proposed. We have effectively stepped out of the early universe by spatial expansion. Any observations that we make, must take into account the fact that our clocks are ticking faster than any (virtual clocks such as supernovas) we observe directly in the past. In effect if we look back far enough, we should see these clocks stop ticking all together. If we don't, then there must be something fundamentally wrong with our universe (We all know our mainstream theories are written in stone, right? ).
We don't have to account for the fact that our clocks are ticking faster that is the point. Since the clocks back then where all ticking at even more at the same rate there is nothing to say. Wether or not you realise it your are swapping variables in different concept. If you went back to 1 second after the big bang there would not be any place, in the what is now become our visible universe, that the time would be any different to any significant amounts. To have time dilation you effectively need to be able to bring the clocks back together to compare.

So at the big bang place 2 cesium atoms anywhere in the the universe.
Then wait 91,926,317,700 oscillations on each atom and then bring those to atoms together.
They'll have almost the exact same value because they didn't fall into or come out of any gravity well that the other atom wouldn't have encountered.
The number of oscillations will be very close to 91,926,317,700 + the number of oscillations they experienced during the trip and as long as those atoms where accelerated and decelerated at the same rate then they'd show the same time. Repeat this a few trillion times and you'll see that they are almost spot on every single time.

Now do this but instead of 91,926,317,700 oscillations we wait 3.988754007028161525x1027 oscillations. You'll see the average ratio is much greater. This is because while the density has decreased over all the differences in density from any 2 random points has increased.

I never said anything about our theories being set in stone. Just pointing out that saying something like "the first second of the universe would have taken billions of seconds" is misleading. Even so if we take those random cesium pairs most would be very close to the same number of oscillations even after 3.988754007028161525x1027 IE the time dilation difference between us on the surface of Earth orbiting the sun orbiting the centre of the milky way compared to intergalactic space is only in the 5-6th decimal place.

Your statements may lead people to believe that the age of the universe being ~13.75 billion years old is totally arbitrary. It is a bit like saying that if you had a twin and they where put on a 747 at birth and flew constantly for 90 years then landed for your 90th birthday that your twin would not be 90 years old to because they experience a few less seconds then you did.

16. Originally Posted by csmyth3025
Thanks WayneFrancis for your reply. I was going to respond to a1call's proposition in the same way - but you said it much better.

Actually, I posed the very same conjecture a long time ago in another thread elsewhere and got the same response.

Still, there remains a nagging question in my mind about whether one second in the early universe is comparable to one second as we perceive it today. The reason for this, of course, is that the gravitational field in the early universe was presumably much stronger back then as opposed to the gravity experienced by our earthbound clocks.

Although one second was undoubtably one second for "observers" in the early universe, we are, in a sense, now the outside observers viewing those early events in a distant and greatly reduced gravitational field. It's hard for me to reconcile the notion of the "faster" clocks on GPS satelites vs the "slower" ground-base clocks here on Earth (due to the stronger gravitational field) with the notion that big bang nucleosynthesis transpired over a period of about 17 minutes of "our" time.
(ref. http://en.wikipedia.org/wiki/Big_Ban...ucleosynthesis )

I think this question might be a good subject for a new thread (or, perhaps, another one has alredy been started on this subject - does anyone know?).

Chris

Edited to correct spelling errors
See there is a big difference between the early universe and satelites used for GPS. Satelites are can be moved up out of the gravity well and back in. How do you propose to do the same with the early universe? That is the difference. We can compare clocks by sending them away and bringing them back. This works for both GR and SR. The clocks start out synced, one goes out of sync with the other then if they are brought back they are back in sync with regard to their current rate but they'll read different times. The early universe there was no lifting one of them out of a gravity well that the other wouldn't also be lifted out of by expansion. This means the end result is the clock all tick at the same rate. IE there was never enough change in the gravitational field to make any real difference. Heck even today there is hardly enough change in the gravitational field from one place to another to make a difference unless you get near those freaky black holes.

To be clear here is another thought experiment

in the early universe, ~10 seconds. Find me 2 spots in the universe where, according to GR, they'd have a significant amount of time dilations. I'll only ask for a time dilation of 1 part in 1,000.

Today we can do this with ease.

It would be like complaining that a marathon runner didn't run a 52.195km because 13 billion years ago those 2 points in space where not 52.195km apart.

17. On the age & expansion of the universe

Originally Posted by pkarnes
I have seen on several shows that we know how old the universe is by the rate of expansion of the universe as we know it now.
Reality is slightly mushier than this sentence implies. The age of the universe can never be determined independently from a theory of space-time. Change the theory and you change the age, even if the observational input remains unchanged. So to say we "know" the age of the universe implies a degree of certainty that in reality does not exist. It is true that general relativity is a widely supported theory and unlikely to be seriously flawed. But I would say that "know" isn't quite the right concept to apply to an age derived from the convolution of theory & observation, regardless of the theory.

Originally Posted by pkarnes
My question is how do we know this rate of expansion, as well, if we dont know how far the inflation of the universe took space, ...
Inflation is a theoretical concept, but one that can be tested by observation. In all theories the inflationary period of the infant universe lasts no more than the tiniest fraction of a second. The entire inflationary epoch is over before the universe has reached the age of 10-30 seconds. So inflation is no problem as regards the tens of billions of years in the age of the universe.

As for the rate of expansion, that too is not independent from models. Edwin Hubble derived the distances to several galaxies using cepheid variable stars, and compared the distances to the redshifts of the galaxy spectra (most of which were measured by Vesto Slipher at Lowell Observatory), and from that was the first to observationally derive a redshift-distance relationship (Hubble, 1929). This redshift-distance relationship is the key. The Hubble Key Project was the primary motivating factor behind the advent of the Hubble Space Telescope. They measured distance using Cepheid variable stars, but at far greater distance than could Edwin Hubble. The redshifts are the result of a relative motion of the galaxy away from the observer. But the one single redshift for the galaxy results from the sum of two motions, the "peculiar" local motion of the galaxy in its local environment, and the "cosmological" motion of the galaxy carried away with the expanding universe. The idea is to measure the largest possible distances, because the relative size of the peculiar local motion is smaller over larger distances. So the local motion has to be modeled based on our knowledge of the local environment, the remnant being the cosmological motion, which is the rate of expansion. In 1998 astronomers reported their discovery that very distant supernovae were farther away than they should be in distance, given their redshift (deriving the distance from the brightness of the supernovae) and that is the genesis of the idea that the expansion rate is actually accelerating, rather then slowing down (Reiss, et al., 1998; Perlmutter, et al., 1999).

That's it in a nutshell, with lots of details left out.

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