what is the universe expanding into?

[Martin]

... like the space around it.

and the idea that we just dont have the "equipment" to visualize ... seems to me like sheer laziness.

 

It's fine if it seems to you like laziness, things seem different to different people.

To me what feels like laziness is imagining a surrounding.

 

Because that is what we are used to. In our experience things that have geometry we look at from the outside and see their shape as they exist immersed in our 3D.

 

You have to work to train your mind to imagine experiencing a geometry from the inside---with no clue of any surround, no reason to suppose a surround of any sort exists. What would it be like if all existence were concentrated on or in this particular geometry context? Could I look off in some direction and see the back of my head? What would the most distant object look like? Would it be very large or very small? In what direction would it be? What would traveling be like?

 

It takes work to imagine the experience of different kinds of geometry from the inside.

So I don't think of it as lazy. I think what is lazy is visualizing the universe from the standpoint of someone outside it. And it doesn't teach you much either because that is not how observational data is presented.

 

To understand observational cosmo data (like how the microwave background measurements and counts of galaxies at various distances, and supernova data is interpreted) you should have a feel for the effects of geometry experienced from the inside. So working to train your imagination to go that way can have some practical benefit.

[NowThatWeKnow]

so its like space is stretching, i understand, and i like it. but when you inflate a balloon it gets bigger, hence expanding into something, like the space around it.

and the idea that we just dont have the "equipment" to visualize space, although legit, seems to me like sheer laziness.

 

When my parents were young the Milky way was the known universe. Today that 100,000 ly has turned into 13 billion ly. The expansion of space and the speed of light keeps us from seeing any further (at this time). I do not see it as laziness.

[Sayonara]

and the idea that we just dont have the "equipment" to visualize space, although legit, seems to me like sheer laziness.

Well then get off your lazy backside and invent it

[cameron marical]

you guys are right, im sorry. its not lazyness at all, i was just kind of pissed my question wasnt getting agreed with. no, i know when to stop and say im wrong, and im wrong. i agree, and finally understand{ i dont know why i wasnt getting it, just something didnt click}. i don like to consider myself a simpleton, but a 15 year old still has a long way to go i guess.

[NowThatWeKnow]

you guys are right, im sorry. its not lazyness at all, i was just kind of pissed my question wasnt getting agreed with. no, i know when to stop and say im wrong, and im wrong. i agree, and finally understand{ i dont know why i wasnt getting it, just something didnt click}. i don like to consider myself a simpleton, but a 15 year old still has a long way to go i guess.

The thing is, it is possible that you are not wrong. Have you heard any one here that had the answer? You are doing fine for 15.

[cameron marical]

thanks man.

[Martin]

...any one here that had the answer? You are doing fine for 15.

 

That's right.

 

One good thing about NowThat is that he went and tried the Ned Wright cosmology calculator. Tried various stuff on his own and came back with questions.

 

It's a hands-on way to get experience with the standard cosmo model.

 

How about you Cameron, would you be up for that?

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

 

or just google "wright calculator" and you will get it.

 

on the left side of the screen, put in different Z. Leave the rest alone for the time being.

 

The cosmic microwave background redshift is z = 1090. Put that in and see what the travel time is, and how far away the matter is that emitted it. And so on.

 

Or put in z = 6.7 which is the redshift of some of the most distant galaxies imaged so far.

 

The main distance to use is the "comoving" distance which is what works in Hubble law.

But you might want to ask about some of the other stuff.

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

 

Also Cameron, can I recommend the Einstein-Online pages that I have the link to in my signature?

It's the public outreach website of a top research institution. A lot of Wikipedia is not bad but this is probably somewhat more reliable.

Edited January 26, 2009 by Martin

[cameron marical]

ill try it out, thanks.

[Airbrush]

I don't like the balloon analogy because it expects you to deny your own common sense that the universe is 3 dimensional. I prefer the supernova analogy for the universe. The universe is like a large-scale supernova and our entire visible universe is part of the expanding outer shell which surrounds an immense void, quadrillions of light years across, that may have a SUPER-supermassive black hole at the center of it all.

[Martin]

I don't like the balloon analogy because it expects you to deny your own common sense that the universe is 3 dimensional. I prefer the supernova analogy for the universe. The universe is like a large-scale supernova and our entire visible universe is part of the expanding outer shell which surrounds an immense void, quadrillions of light years across, that may have a SUPER-supermassive black hole at the center of it all.

 

It is not a good physical analogy for several reasons.

One is that the expanding outer shell would need to be expanding at several times the speed of light. And all the matter in the shell would be breaking the speed limit.

 

Another is that the outer shell would not be really 3D. It would be 2D like the surface of the balloon plus with some finite thickness. So it wouldn't look the same in all directions. There would be a preferred direction back towards the center of the explosion.

[Airbrush]

It is not a good physical analogy for several reasons.

One is that the expanding outer shell would need to be expanding at several times the speed of light. And all the matter in the shell would be breaking the speed limit.

 

Another is that the outer shell would not be really 3D. It would be 2D like the surface of the balloon plus with some finite thickness. So it wouldn't look the same in all directions. There would be a preferred direction back towards the center of the explosion.

 

The opposite sides of our visible universe are already separating at greater than light speed. Also, if the furthest we can see in every direction is about 12 Billion light years, and the quasars that we see are actually about twice as far away (2 X 12 = 24 Billion LY) in both opposite directions, because they have been moving away from us at near light speed for over 12 Billion years, then we are already admitting that the outer edges of our visible universe had only a little over 13 Billion years to travel 24 Billion LY in opposite directions, for a combined separation speed of about 48 Billion LY in only a little over 13 Billion years, then the light speed limit is broken anyhow. How do you explain that?

[NowThatWeKnow]

...then we are already admitting that the outer edges of our visible universe had only a little over 13 Billion years to travel 24 Billion LY in opposite directions, for a combined separation speed of about 48 Billion LY in only a little over 13 Billion years, then the light speed limit is broken anyhow. How do you explain that?

 

Airbrush,

Martin pointed me to a really neat calculator that helps put things in perspective.

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

The light from a galaxy that took 12 billion light years to get here started towards us when it was only 4.8 billion light years away. That galaxy is currently 23.58 billion ly away. The space the light traveled through had an expansion rate of 4.9. If you are interested, a few simple rules and definitions are needed to understand the calculator. If you put 3.9 for a value of "z" and click "flat" you may see where the #'s come from.

 

The light speed episode of "the Universe" program said "the only thing faster then light is the expansion of space. This may be the answer to the question. Also, a third party seeing two objects separating at faster then the speed of light does not mean those two objects see themselves separating faster then light. That crazy space math.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html

and

http://www.cthreepo.com/cp_html/math1.htm

[Airbrush]

Thanks for the info NowThat and Martin. I should study the sticky material and some tutorials. Great stuff. Back later.

[Martin]

... really neat calculator that helps put things in perspective.

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

The light from a galaxy that took 12 billion [years] to get here...

 

Good suggestion! It reminds me that Ned Wright has an alternative version of the calculator here:

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

where instead of putting in the redshift z, you put in the travel time (in billions of years, not billions of lightyears ) that the light took to get here.

 

Then it tells you how far away the object was when it emitted the light, and also how far away it is today, as we are receiving the light.

 

The link to the travel time version of the calculator is down near the bottom of the page of the regular version.

 

So you can check. For instance put in 12 for the travel time (12 billion years) and press "flat" (or "general" will work too.)

and it will say that the object was 4.9 Gly from us back then when it emitted the light---and that it is now 23 Gly from us. I rounded the numbers.

 

The regular version of the calculator should give the same numbers if you find the right redshift to put in

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

Yes, I put in z= 3.809 and it checks.

 

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

 

A lot of people make the serious mistake of imagining Big Bang cosmology as an explosion.

The Scientific American had a wonderful article discussing the misconceptions about the Big Bang that plague people. It was published in March 2005 and is still being used at Princeton as astro coursework reading. Unusually good for the SciAm.

I have a link to the SciAm article in my signature. The link that starts ...mso.anu.edu...

The name Big Bang was given to the theory by an enemy of the theory who was promoting an alternative non-expanding cosmogy back in the 1930s. The name Big Bang tends to give people the wrong idea. But it caught on and got embedded in the public language, so we have to use it.

 

Now, as the field is gradually moving away from the idea that there was a singularity, and towards modeling conditions leading up to the start of expansion, we increasingly hear the term Big Bounce. I think the appeal has something to do with alliteration.

 

Anyway any sort of physical explosion is a misleading image and gives people the wrong idea. In an explosion, crud moves thru space and that simply doesn't fit the reality. We know there is a speed limit for crud moving thru space and that is way too slow. What you have to get your mind around is that stuff is sitting still, while (because geometry is dynamic) distances between stationary objects are increasing.

You can see this clearly in NedWright's balloon model because the photons (the colored wriggly things) are moving over the balloon surface gradually changing their longitude and latitude---that's what motion is in the model. And the galaxies (the white things) are at rest---stationary---they don't change their longitude and latitude.

Ned Wright balloon model:

http://www.astro.ucla.edu/~wright/Balloon2.html

 

Here's the Cosmo Basics sticky thread. It has several of these links

http://www.scienceforums.net/forum/showthread.php?t=35925

Edited January 27, 2009 by Martin

[NowThatWeKnow]

Good suggestion! It reminds me that Ned Wright has an alternative version of the calculator here:

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

where instead of putting in the redshift z, you put in the travel time (in billions of years, not billions of lightyears ) that the light took to get here...

 

...Anyway any sort of physical explosion is a misleading image and gives people the wrong idea. In an explosion, crud moves thru space and that simply doesn't fit the reality...

 

I like that calculator better. At first I thought they left out "z" but then I saw it at the top.

 

Even if the Big Bang was an explosion of singularity or a region, it seems it is not driving what we observe today. Maybe the BB ran out of energy and something else took over the expansion.

[Martin]

...

Even if the Big Bang was an explosion of singularity or a region, it seems it is not driving what we observe today.

 

NowThat,

aaaarrrrgh! Please don't use the word singularity as if it was something real that actually existed!

Professionally, in cosmology, the word is used as a time-marker, it refers to the moment in time where the old classical model breaks down and stops computing. Only the public believes that there is actually a physical thing in nature called a singularity!

 

Since they don't exist in nature, you couldn't have an explosion of one.

 

In the new models, which don't break down, you still have the t=0 point.

You can still call that time-marker the "classical singularity" or as one of the experts in the fields calls it the "putative singularity".

It's just that the new model keeps on computing and continues on back before the t=0 point where the old model went bust.

 

The original meaning of singularity was in mathematics, a place where a function has a singularity is a place where it fails to be defined. Like the function 1/x isn't defined at zero. Physicists took the word over to mean somewhere a particular theory or math model broke or failed to apply or didn't give meaningful answers. It has a long history, not confined to cosmology, and doesn't necessarily mean that the failure mode is infinite density or infinite curvature. In other branches of physics other things can go haywire besides density and curvature.

 

Anyway it is not a feature of nature, it is a feature of manmade mathematical models. So it misleads people when one refers to a singularity as a physical natural something that could do something, like explode.

 

A singularity is a challenge to improve the theory. There've been a bunch of them in the past that have been fixed by improving theory, and that now no longer exist. They are ex-singularities.

Like the former Soviet Union, or the ex-parrot in Monty Python.

[NowThatWeKnow]

NowThat,

aaaarrrrgh! Please don't use the word singularity as if it was something real that actually existed!

...So it misleads people when one refers to a singularity as a physical natural something that could do something, like explode...

 

Hey, I started with "Even if". Isn't that worth something? Some of your post sound like NowThatWeKnow and that makes me go aaaarrrrgh!

[empty]

IMO at some point the universe will stop expanding .maybe the reason will be the reverse gravity of the universe and start back to point zero .

 

there are a lot of things we didn't take it maybe one of them is time , our universe made of galaxies and that made of stars . some of them died by explosion and others became a black hole . my point is we can't imagine the expansion of universe if those things disappear or vanished . those things will die soon or later before they can expand .all people here imagine the expanding things but they didn't take changing thing ( time ).

[Sayonara]

IMO at some point the universe will stop expanding .maybe the reason will be the reverse gravity of the universe and start back to point zero .

As entitled as you are to your opinion, it contradicts the observable evidence.

[Airbrush]

The universe is space-time. The universe is expanding into empty space. Beyond there is no matter at all, not even a few atoms per cubic LY, so it is not space-time, it is only space, black, cold empty space. Nothing is more simple than that.

[iNow]

Space is itself something, though, so you're pretty much contradicting yourself repeatedly there with your simplified and over-confident assertion, airbrush.

[NowThatWeKnow]

The universe is space-time. The universe is expanding into empty space. Beyond there is no matter at all, not even a few atoms per cubic LY, so it is not space-time, it is only space, black, cold empty space. Nothing is more simple than that.

 

Maybe not simple and far from fact but it is easier to think about than a universe with a boundary or one without.

[Airbrush]

Space is itself something, though, so you're pretty much contradicting yourself repeatedly there with your simplified and over-confident assertion, airbrush.

 

Space is nothing. Space-time is something. Space-time is expanding. Dark energy is a property of space-time. We can see only space-time.

 

Have they confirmed experimentally that virtual particles pop in and out of empty space? If so, that may only apply to space-time. I am trying to make a distinction between "space-time" and "space". Space-time is within the universe, space is outside of space-time.

Edited February 13, 2009 by Airbrush

[Royston]

Space is nothing. Space-time is something.

 

Perhaps you'd like to explain how you can have one without the other in a physical sense, and please don't repeat your argument that 'empty space' exists outside the Universe (that goes against basic cosmology). Even treating space as purely mathematical e.g a metric http://en.wikipedia.org/wiki/Metric_space, it has properties there's something to work with.

 

Please try not to make flat out statements, without backing them up.

[Airbrush]

"Empty-space" is pre-big-bang potentiality. "Space-time" is post-big-bang actuality. Something does not come from nothing. I stand corrected. Empty-space is something, the "program" of existence. Sorry I cannot back up anything on this peculiar subject because it is cutting-edge. I am only exercising logical speculation.