Universe age

[David Levy]

The science has an explanation for those galaxies which are located at almost 14 billion light years away from us.

However, if one day we will discover a galaxy at 50 (or 500) Billion light years away (or at infinite distance) – is it going to set any change in our understanding about the age of the universe?

Edited April 17, 2015 by David Levy

[ajb]

Yes, I suppose so. Seeing objects that are seemingly too far away for you to see them would upset the standard model of cosmology.

[Strange]

A couple of points, the galaxies that we see at about 13 billion light years away are now more than 40 billion light years away. There are, beyond that, almost certainly galaxies which are even further away. Probably including 500 billion light years away. But we can never see them because there hasn't been enough time for the light to reach us. (And the light never will reach us because the universe is expanding.)

 

So, if we detected a galaxy that we thought was more than 50 or 500 billion light years away (or more than 14 billion years old) then, yes, obviously that would challenge existing models. Which would be very exciting.

[imatfaal]

Firstly - your initial presumption is incorrect. We can see galaxies which are a bit under 46 billion light years away - that is the limit of the observable universe. Their light has been travelling for 13.8ish billion years. Space has expanded as well so the distance is greater than 13.8 Glyr. Please note that many far distant cosmological objects are given with a light travel distance - which is not the same as the cosmological proper distance / comoving distance

 

If some measurement way beyond that could happen then it would show all our conceptions are incorrect. It is very very unlikely - it would require a sea-change in our understanding and would mean all bets are off.

 

Frankly I cannot conceive of a situation in which we would be able to measure the age of a galaxy / the remoteness of that sort of range. It would imply that all our fundamentals are incorrect - and we would be using those very fundamentals to make the measurement in the first place. That is to say it would not require a single measurement - it would require a complete rejig of all cosmology before the measurement could take place

Edited April 17, 2015 by imatfaal
multiple cross-post

[Spyman]

If we one day find a way to observe neutrino radiation from the early universe then it's very likely that the current size of the observable universe will increase substantionally, without any need to change the current estimated age of the universe.

 

Edit: I was wrong, further explanation in post #8.

 

The cosmic neutrino background (CNB, CνB) is the Universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos.

 

Like the cosmic microwave background radiation (CMB), the CνB is a relic of the big bang, and while the CMB dates from when the Universe was 379,000 years old, the CνB decoupled from matter when the Universe was 2 seconds old. It is estimated that today the CνB has a temperature of roughly 1.95 K. Since low-energy neutrinos interact only very weakly with matter, they are notoriously difficult to detect and the CνB might never be observed directly. There is, however, compelling indirect evidence for its existence.

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

Edited April 17, 2015 by Spyman

[Strange]

The cosmic neutrino background is only about 360,000 years older than the microwave background. I think that is about 1% of the error in the current estimate of the age of the universe, so it doesn't sound like it would make a significant difference in that sense. But it would obviously give us a lot more information, if it were detectable.

[imatfaal]

If we one day find a way to observe neutrino radiation from the early universe then it's very likely that the current size of the observable universe will increase substantionally, without any need to change the current estimated age of the universe.

...

 

But the question was regarding macro-structures - at the point of the CvB there were no baryons let alone galaxies. We can only observe galaxies from when galaxies started to form - the furthest protogalaxies are a light-travel distance / age of about 13.3 Glyr/Gyr.

 

The CvB can only show us that which was in existence at the point in which matter started to decoupled from interacting with neutrinos - ie a soup of positrons, electrons and photons (and not the photons obviously)

The cosmic neutrino background is only about 360,000 years older than the microwave background. I think that is about 1% of the error in the current estimate of the age of the universe, so it doesn't sound like it would make a significant difference in that sense. But it would obviously give us a lot more information, if it were detectable.

 

I am currenly trying to get my head around what the comoving distance of the surface of neutrino decoupling will be.

[Spyman]

If we one day find a way to observe neutrino radiation from the early universe then it's very likely that the current size of the observable universe will increase substantionally, without any need to change the current estimated age of the universe.

I am sorry but I was wrong. I didn't think it trough entirely and was in a hurry.

 

The observable universe is only about 2% larger than the visible universe and includes everything that it is theoretical possible to detect, independent of whether we have the technology to do so or not.

 

Any relic neutrinos from before the CMBR must thus still be within our observable universe.

 

The observable universe consists of the galaxies and other matter that can, in principle, be observed from Earth at the present time because light and other signals from these objects has had time to reach the Earth since the beginning of the cosmological expansion. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical volume (a ball) centered on the observer. Every location in the Universe has its own observable universe, which may or may not overlap with the one centered on Earth.

 

The word observable used in this sense does not depend on whether modern technology actually permits detection of radiation from an object in this region (or indeed on whether there is any radiation to detect). It simply indicates that it is possible in principle for light or other signals from the object to reach an observer on Earth. In practice, we can see light only from as far back as the time of photon decoupling in the recombination epoch. That is when particles were first able to emit photons that were not quickly re-absorbed by other particles. Before then, the Universe was filled with a plasma that was opaque to photons.

 

The surface of last scattering is the collection of points in space at the exact distance that photons from the time of photon decoupling just reach us today. These are the photons we detect today as cosmic microwave background radiation (CMBR). However, with future technology, it may be possible to observe the still older relic neutrino background, or even more distant events via gravitational waves (which also should move at the speed of light). Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination-and the observable universe, which includes signals since the beginning of the cosmological expansion (the Big Bang in traditional cosmology, the end of the inflationary epoch in modern cosmology). According to calculations, the comoving distance (current proper distance) to particles from the CMBR, which represent the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years), about 2% larger.

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

[Mordred]

I am currenly trying to get my head around what the comoving distance of the surface of neutrino decoupling will be.

Roughly 1 second after BB, which is later than inflation. So you still won't be able to directly detect inflation.

[imatfaal]

Roughly 1 second after BB, which is later than inflation. So you still won't be able to directly detect inflation.

 

Everytime I try a calculation of this form I find myself tying myself in knots. we need to know the equivalent to red shift of the neutrinos to work out the background expansion since roughly 1-2 secs post BB - and the actual speed through space.

 

The weak force cools out and neutrinos decouple at 10^10K if my preliminary reading is correct. Does this mean that the neutrinos are cooled from ten billion kelvin to 1 kelvin? That's a huge redshift - or from 2-3MeV to around 1x10^-4 eV. Is that all attributable to background expansion?

[Mordred]

 

Everytime I try a calculation of this form I find myself tying myself in knots. we need to know the equivalent to red shift of the neutrinos to work out the background expansion since roughly 1-2 secs post BB - and the actual speed through space.

 

The weak force cools out and neutrinos decouple at 10^10K if my preliminary reading is correct. Does this mean that the neutrinos are cooled from ten billion kelvin to 1 kelvin? That's a huge redshift - or from 2-3MeV to around 1x10^-4 eV. Is that all attributable to background expansion?

Not completely all but a huge factor is. Take the background temperature, then use the Fermi Dirac equation for combined species of neutrinos. This will give the neutrino temperature.

 

Today with blackbody temperature 2.7 k the neutrino temperature is roughly 1.9 k.

 

The other problem is the standard cosmological redshift formula needs corrections. If your after the redshift of neutrinos, this is due to two phase ,matter dominant and radiation dominant eras. These two eras have influence upon redshift due to the different expansion rates, temp and pressure via the equations of state.

 

Probably easier to just backward extrapolate the distance via the acceleration equation.

 

Here is one related paper probably help

 

http://arxiv.org/abs/1304.5632

 

The result should be roughly at a distance near 45 to 46 billion light years. As the cosmological event horizon is also the region of shared causality.

However I just ran across this article the massive neutrinos will travel slower.

 

http://physics.aps.org/story/v24/st15

Confuses the issue further.

Currently looking at this thesis paper

 

http://www.google.ca/url?sa=t&source=web&cd=9&ved=0CDgQFjAI&url=http%3A%2F%2Fwww-library.desy.de%2Fpreparch%2Fdesy%2Fthesis%2Fdesy-thesis-05-024.pdf&rct=j&q=distance%20to%20cosmic%20neutrino%20background%20&ei=WDIxVYvRFcWvyAScjIDgBw&usg=AFQjCNG5luClDfbtS6eRi-7q9Or7Xsj90Q&sig2=2lEDhxKO1o67-M0giXG4zw

(I'll have more time later today to look at the calcs in greater detail)

Located Dodelsons paper in regards to the second link.

 

http://www.google.ca/url?sa=t&source=web&cd=11&ved=0CBoQFjAAOAo&url=http%3A%2F%2Farxiv.org%2Fpdf%2F0907.2887&rct=j&q=distance%20to%20cosmic%20neutrino%20background&ei=e0AxVdqKFYT6yASXoIHwCA&usg=AFQjCNHrxyfLWo_WV4Wr6ZOSOZXOLsDxZw&sig2=TCOdofb7-k195qXYtUFCfQ

[David Levy]

Firstly - your initial presumption is incorrect. We can see galaxies which are a bit under 46 billion light years away - that is the limit of the observable universe. Their light has been travelling for 13.8ish billion years.

 

- How could it be that we see galaxies at a range of 46 Billion light years away while their light has been traveling for only 13.8 Billion years?

- Is it 46 billion years for any direction from us? so can we assume that the total diameter of the visible universe should be at the range of 92 Billion years?

[Mordred]

Universe expansion, as the light travels to us the space behind and ahead of the light path expands

 

Yes 92 billion light years is the radius.

http://cosmology101.wikidot.com/redshift-and-expansion

[StringJunky]

...Yes 92 billion light years is the radius. diameter

http://cosmology101.wikidot.com/redshift-and-expansion

[Mordred]

Thanks String was in a hurry lol

[StringJunky]

Thanks String was in a hurry lol

No prob.

[pavelcherepan]

Just to clarify some confusion I'm having.

 

So if every observer in the Universe has its own observable Universe (I'm on fire with tautologies today!) would those be the same size from the perspective of such an observer? I mean right now for us on the Earth the observable Universe is some 46 bly and then for another observer somewhere in Andromeda galaxy it is the same since the age of the Universe should be the same for both.

 

And another observer in NGC4696 at 150 mly will have the same size of observable Universe too.

 

With that in mind can we constrain the size of the entire Universe in any way or should it be deemed infinite?

[StringJunky]

I think it's the same for everyone everywhere. The measurement of increasing velocity of a receding galaxy is an artifact of the expansion; the further away it is the faster it appears/measures to be receding. Locally, the rate expansion is the same for everyone everywhere. Don't conflate the increasing rate of cosmological expansion with the recession velocity which is an apparent measurement. I find it easier to visualise myself standing on the 2D surface of an expanding sphere and everything is happening on that surface around me.

Edited April 18, 2015 by StringJunky

[Mordred]

 

Imatfaal I'm not sure I trust my calculations but I'm getting roughly z= 6*10^9 for neutrino background based on 1MeV decoupling.

[David Levy]

Universe expansion, as the light travels to us the space behind and ahead of the light path expands

 

Yes 92 billion light years is the radius.

http://cosmology101.wikidot.com/redshift-and-expansion

 

Thanks Mordred

Simple & direct explanations

 

 

So, if we detected a galaxy that we thought was more than 50 or 500 billion light years away (or more than 14 billion years old) then, yes, obviously that would challenge existing models. Which would be very exciting.

 

Let's assume that one galaxy is located 13 Billion light years away from us in one side of the visible universe, while in the opposite side there is another galaxy which is also located 13 Billion light years away.

Therefore, the total distance between those two galaxies could be up to 26 Billion light years.

So, does it mean that the Universe might be older?

Edited April 18, 2015 by David Levy

[StringJunky]

 

Thanks Mordred

Simple & direct explanations

 

 

 

Let's assume that one galaxy is located 13 Billion light years away from us in one side of the visible universe, while in the opposite side there is another galaxy which is also located 13 Billion light years away.

Therefore, the total distance between those two galaxies could be up to 26 Billion light years.

So, does it mean that the Universe might be older?

The maximum extent to where we can see is 46 billion light years. It has expanded, from you, 46BLyrs distance in 13Byrs of time.

Edited April 18, 2015 by StringJunky

[Strange]

 

Let's assume that one galaxy is located 13 Billion light years away from us in one side of the visible universe, while in the opposite side there is another galaxy which is also located 13 Billion light years away.

Therefore, the total distance between those two galaxies could be up to 26 Billion light years.

 

As already noted, the distance between them is more like 90 billion light years.

 

 

So, does it mean that the Universe might be older?

 

No. Don't you think someone would have noticed, if that was the case.

[Mordred]

Imatfaal I'm not sure I trust my calculations but I'm getting roughly z= 6*10^9 for neutrino background based on 1MeV decoupling.

Looks like I'm close according to Ned Wright's redshift calculator 1.055 sec is z=5*10^9

http://www.astro.ucla.edu/~wright/CosmoCalc.html

Edited April 18, 2015 by Mordred

[swansont]

 

Let's assume that one galaxy is located 13 Billion light years away from us in one side of the visible universe, while in the opposite side there is another galaxy which is also located 13 Billion light years away.

Therefore, the total distance between those two galaxies could be up to 26 Billion light years.

So, does it mean that the Universe might be older?

 

Since 26 < 92, no.

[David Levy]

Let's use different approach.

With regards to the most distant galaxy (which is located more than 13 billion light years away from us):

Let's assume that it will be discovered that the age of the stars in this galaxy are similar to the stars in the Milky Way. Hence, there are young stars but some very old stars. So what could be the impact of a 10 billion old star discovery in that far end galaxy?

Edited April 18, 2015 by David Levy