Age of Universe: Seeing More than 13.5 Billion Yrs

[hellfire]

However, http://adsabs.harvard.edu/abs/1994ApJ...429..491S apparently has been published. But after reading it, I don't think it makes a lot of sense. Maybe we can get some other people to comment on this paper.

I don't think this paper is right. The reasoning might apply for free particles, but most of the matter in the universe is bounded to interactions. In that case the behaviour is different, see for example:

In an expanding universe, what doesn't expand?
http://www.arxiv.org/abs/gr-qc/0508052

 

[BoomBoom]

wavelength now/wavelenght then = spatial scalefactor now/scalefactor then = (or in more casual terms) "size of U now/size of U then"

Ok, another layman thought here:

I was reading in some other threads about how expansion is not observable locally, I presume because we are part of a local galaxy cluster or group that has an effect on expansion rates due to gravity interactions.

So I was thinking that all our experience with how light behaves has been in this context (as part of a solar system within a galaxy that is part of a group of other galaxies). All of our assumptions about the properties of light are within this framework.

My point being that perhaps it behaves differently when separated from gravitational effects so that as light leaves a cluster region and enters a large void region, the tug of gravity from the cluster it left as it enters a vacuumous region along with the pull of gravity as it approached us would stretch it and thus give the optical illusion that everything was migrating away from us?

It just seems odd that this great accelerating expansion is virtually undetectable in our local (and present) part of the universe.

 

[Chronos]

Expansion is much too small to observe locally. At 72 meters per megaparsec, local effects are nonexistent. Assuming it is a force, such as gravity, it may only have consequences in the vast empty spaces between galaxies.

 

[marcus]

Expansion is much too small to observe locally. At 72 meters per megaparsec, local effects are nonexistent.

I think you meant to say "72 kilometers per second" instead of "72 meters"

the first is a recession speed, the second is a length and wouldn't make logical sense in the context.

 

[marcus]

Ok, another layman thought here:

I was reading in some other threads about how expansion is not observable locally, ...

My point being that perhaps it behaves differently when separated from gravitational effects so that as light leaves a cluster region and enters a large void region, the tug of gravity from the cluster it left as it enters a vacuumous region along with the pull of gravity as it approached us would stretch it and thus give the optical illusion that everything was migrating away from us?

It just seems odd that this great accelerating expansion is virtually undetectable in our local (and present) part of the universe.

It sounds like you are skeptical of expansion. You don't want to believe in it. My attitude is that people should be allowed to believe what they want and whatever you want to believe is fine.

I only think it would be a good idea if everyone in the discussion learns about and understands something of the mainstream consensus model cosmology.

Along those lines, I can explain the mainstream view and why what you are saying doesn't make sense, but I don't want to ARGUE or try to PERSUADE you of anything. You should go on believing whatever feels right to you.
============

redshifts are not the only evidence for expansion. they are part of a huge body of interlocking different kinds of evidence supporting GR
GR does not predict expansion of distances between bound-together objects. So it is no surprise that we don't see expansion redshift locally.
We see a huge amount exactly where GR tells us to expect it.

you offer an alternative explanation for redshifts, but it is faulty:
light IS redshifted by leaving a concentration of mass and this has been observed ON EARTH in labs. it is also blueshifted as it approaches a concentration of mass----so in a rough sense the effects "cancel". In your alternative explanation you get half of it backwards---you describe a gravitational redshift at both ends of the trip. But that's all right, what you describe wouldn't work anyway, because:

this socalled gravitational redshift has been measured and is not enough to explain the cosmological redshift. it does not even come within a factor of 1000 of being able to explain.

(also it is a bad idea to think of gravity "tugging" on light and "stretching" it as if it were a force acting on a spring====lightwaves aren't material objects===material analogy can be misleading)

the CMB light has been redshifted by a factor of around 1000 and it does not come from any concentration of mass! Your picture of light getting redshifted by "leaving" another galaxy doesn't apply. CMB light came from space uniformly filled with ionized gas before any stars and galaxies had formed

You are welcome to disbelieve this, BoomBoom But you are struggling against a vast body of consistent observation. People have been trying to find alternative explanations for this or that feature ever since the 1930s.

they never manage to find a way to explain away ALL the different sorts of evidence.

just as you are doing with your "gravity tugging" explanation of the redshift, there have been people who made a big effort to promote other alternative explanations like "tired light" which work better than yours. these are professional astronomers I am talking about and they have worked hard at it. but for 70 years they've tried and the alternatives just poop out.

Of course we all know the standard model is WRONG. It is based on Einstein's 1915 theory of gravity and we know for sure that is wrong because it predicts singularities (breaks down in certain situations)

And people are working on FIXING the basic gravity theory and perfecting the cosmological model.

this is happening----but the improved models will still have distances expand!

The improved model cosmology which is emerging from the confusion of many researchers' efforts will NOT BE ANY MORE ACCEPTABLE TO YOU.

We know GR and LCDM are wrong, and they are being improved. But what is wrong about them is not what you find wrong, so the progress under way will not make it better for you.

right now, I accept GR and LCDM provisionally, as amazingly good fits to reality despite their obvious flaws-----and I am trying to glimpse the vague outlines of the improved picture that will gradually come to replace them.

 

[Chronos]

Correct, 72 km/s. I was wondering why all my calculations were off by 1000!

 

[BoomBoom]

I only think it would be a good idea if everyone in the discussion learns about and understands something of the mainstream consensus model cosmology.

I agree and thank you for the education. I have learned much since coming here.

I apologize for my uninformed speculation and will refrain from speculating in the future.


On another note:

I was curious about how they determine the mass of galaxies. Is it assumed that most stars have solar systems such as ours or are individual masses determined from observations of surrounding materials?

When I hear predictions about the mass of the universe, I can't help but think it must have a HUGE margin of error.

 

[marcus]

..

When I hear predictions about the mass of the universe, I can't help but think it must have a HUGE margin of error.

that is something that professionals (grad student cosmologists) can speak to like SpaceTiger and Wallace

you are necessarily talking mass DENSITY, that is mass per cubic lightyear volume. because nobody knows what the volume is.

I was curious about how they determine the mass of galaxies. Is it assumed that most stars have solar systems...

You can tell the mass of a spiral galaxy by how fast the edges are whirling around, which you can tell by doppler, if you can see it edge on. part of the edge is coming towards and part is going away and the dopplershift tells the speed.

that is similar to how you tell the mass of the sun----by how fast a planet (at some given distance) whirls around it.

Then if you know the mass of spiral galaxies you can match that up with their luminosity---how much light they make (and adjust the scale for various minor corrections). brighter means more and more means more massive. you use empirically discovered relationships.

And then you can use that mass/luminosity scale to tell the masses of ALL galaxies, not just the spiral ones.

============

and also you can assume UNIFORM DENSITY on average and if you do that then you only have to estimate the mass per cubic lightyear in a representative sample volume like space around the Local Group and halfway out to the next cluster. Or some larger sample box of space.
You measure inside that box, by the mass-to-light ratio and the rotation of spirals, and then you just ASSUME that the density outside the box is the same as inside.

And they have gotten very good at this so the estimates of matter density are surprisingly consistent. You can come in and pick an entirely different box and (if it is big enough to contain the average and not some fluke) it will turn out to have the estimated density. The universe is pretty uniform.
============

There is another angle which depends on CURVATURE. What I just told you doesn't depend majorly on Gen Rel, the ruling theory of gravity, which says how mass density (actually total energy density including possible immaterial energy) BENDS SPACE.
Now GR has been tested a lot of ways and people tend to trust it. If you believe GR then you can reckon the overall density of energy (or mass) in space by looking to see how curved it is (and how fast distances are expanding, which is another aspect of curvature).

the massenergy density you get by measuring expansion rate and spatial curvature (which turns out to be nearly zero so the main contributor is expansion)
OUGHT to equal the massenergy density you get by doing these huge galaxy surveys inside these big sample boxes.

My advice is, for starters don't worry about that approach, it is the one that is responsible for a confusing discrepancy that people fudge by saying "dork energy". Study that later
=============
the main thing is they estimate the space density of ordinary and dark matter by actually doing surveys of what is in sample boxes.
Little known fact: astronomers are some of the best statisticians on the planet.

 

[Chronos]

BoomBoom, space is really big, that is all we know for sure. Big enough that we haven't yet seen 'circles in the sky'.

 

[Wallace]

When I hear predictions about the mass of the universe, I can't help but think it must have a HUGE margin of error.

I'm not sure where you have heard such things! As marcus points out what we can make predictions and measurement of is the energy density of the universe, mass per volume. One way we can determine this is by looking at the CMB. The pattern of slight fluctuations in the temperature of the observed radiation is highly sensitive to variations in the energy density of the Universe.

 

[BoomBoom]

BoomBoom, space is really big, that is all we know for sure.

I know, this is precisely why it is difficult to grasp the concept of it ever being "really small".

 

[marcus]

When I hear predictions about the mass of the universe, I can't help but think it must have a HUGE margin of error.

As I said, it's really up to Wallace or SpaceTiger to tell you what the current ideas of the margin of error are. I think they are surprisingly narrow like around 10 percent. Not huge anyway.

The thing is you can pick your sample box. The universe is remarkably uniform and there is so much data. Whereever you choose to look and measure you find that it's about the same density!

I actually think the density of the universe is one of those basic, fairly reliable, numbers that one should KNOW BY HEART because it is a basic fact about where we live.

Like the circumference of the earth, or the percentage dry land. I mean, it's your universe, so shouldn't you know by heart what its density is?

 

[marcus]

In case you were wondering, BoomBoom, it is about one joule
per cubic kilometer.

A joule amount of energy is like when you lift a physics textbook about 10 centimeters (4 inches) off the table. That amount of energy.

 

[BoomBoom]

In case you were wondering, BoomBoom, it is about one joule
per cubic kilometer.

A joule amount of energy is like when you lift a physics textbook about 10 centimeters (4 inches) off the table. That amount of energy.

LOL...nice analogy!

This density in an expanding universe should increase the farther we look correct? I am assuming that density is for "today's" universe...

 

[BoomBoom]

I mean, it's your universe, so shouldn't you know by heart what its density is?

Do you happen to know of any good sites out there that may have a decent mapping of our current universe? I know there are many that come up in searches, but was just wondering if you have a favorite. Thanx!

 

[marcus]

LOL...nice analogy!

... I am assuming that density is for "today's" universe...

that's right! Definitely today's space and stars
an instantaneous spatial slice

our idea of what the universe is like right now (May 2007) is based on what we are able to see (by astronomical observation) that it has been like in the past

we can't see the present-day universe, only infer it.
===============

This density in an expanding universe should increase the farther we look correct?

that is right in the sense that the farther out we look the farther back into the past we get a picture of. and farther back in the past the density was higher.

the density in an instantaneous spatial slice is uniform or nearly so once it is averaged out
but what we see when we look out into the layers of past with a telescope is a mix of all the past history of the universe, so it has density changing with depth---different density in each layer

like some elaborate dessert prepared by a master chef just for astronomers.
the manifestly visible sky because of that combination of space and time is really pretty complicated---more complex than the inferred homogeneous spatial slice that we can reconstruct.

have to go, back later

 

[pervect]

The density at any instant of cosmological time should be constant, by the cosmological principle that the universe is homogeneous and isotropic.

When we look, of course, because of lightspeed delays we are seeing an earlier universe.

We expect that ever since the inflationary phase, the universe has been close to the critical density, thus

$$\Omega = \frac{8 \pi G}{3 H^2} \rho \approx 1$$

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

H, the Hubble constant, varies with time (cosomological time), so density ($\rho$) does as well.

 

[BoomBoom]

that's right! Definitely today's space and stars
an instantaneous spatial slice

our idea of what the universe is like right now (May 2007) is based on what we are able to see (by astronomical observation) that it has been like in the past

we can't see the present-day universe, only infer it.
===============

Ok, I was just reading something and the proverbial "light bulb" went off in my head. I think I FINALLY get it. I believe where I was hung up was thinking of light years as being distance and I couldn't see how we could look in any direction and see the same universe when it took so much time for the light from those "distant" galaxies to reach us. So the deep views I referred to in my opening post that I presumed were 24 Glys apart, were actually only 3Glys apart 12 billion years ago.

In my search to find a "map" of the universe I ran across this http://people.cornell.edu/pages/jag8/spacetxt.html" and it was the best explanation I have come across. This I would recommend to any other "laymen" out there having troubles with grasping the concept as I was.

 

[marcus]

OK BoomBoom!

Now for anyone who likes to use the Google calculator, here is something fun to do with Google. You see what Pervect has just written here

$$\Omega = \frac{8 \pi G}{3 H^2} \rho \approx 1$$
...

He is not talking about the energy density, but rather the mass density. But we can stick a c^2 into the formula and change mass to energy.

Try making Google evaluate 3*c^2*H^2/(8*pi*G)
which Pervect is telling you somewhat indirectly is an approximate formula for the energy density of the universe! Very near anyway, see his approx=1 sign.

We can test if this amounts to something like 0.85 joule per cubic kilometer, because then if you multiply it by (km)^3 you should get 0.85 joules!

The formula for H, the Hubble-parameter is this:
71*km/s/Mpc (it says the expansion rate is 71 km per second per Megaparsec)

So you can plug this into the search box at Google:

(km^3)*3*c^2*(71*km/s/Mpc)^2/(8*pi*G)

You can just copy and paste it into the Google window. When I do that, and press "search", what I get back is

((km^3) * 3 * (c^2) * ((71 * ((km / s) / Mpc))^2)) / (8 * pi * G) = 0.851170439 joules

that means the critical energy density of the universe (which it would have to have exactly in order to be perfectly spatial flat) is 0.85 joule per cubic km.

And since we observe that it is very NEARLY spatial flat, we infer that the true energy density is very CLOSE to 0.85 joule per cubic km.

BoomBoom, that is why I told you earlier that the density is around 1 joule per cubic km, lifting a textbook 4 inches-----I didnt want to cut it too fine and say 0.85

 

[BoomBoom]

You can tell the mass of a spiral galaxy by how fast the edges are whirling around, which you can tell by doppler, if you can see it edge on. part of the edge is coming towards and part is going away and the dopplershift tells the speed.

This statement reminded me of something, although it is somewhat unrelated. I was watching a TV program on the Science channel, and since it was from TV, I'm not sure how accurate some of the statements they made are. Please let me know if any of the below statements are inaccurate:

1. so far to date, every galaxy examined has a supermassive black hole at the center.
2. The mass of this black hole correlates with the mass of it's galaxy (I believe they said 0.5%)
3. The speed of revolving stars on the outer edges of the galaxy correlate with the mass of the black hole.

I found this curious because I had always thought that as a black hole devours matter around it, it gains mass. If that is the case, shouldn't we see the mass of galaxies get smaller as the black hole consumes matter and therefore see the ratio of mass (BH/Galaxy) smaller the further out we look and larger as we look closer to home?