We’re ready to complete our trilogy of discovery about the universe. We’ve learned that it has no center; rather everywhere is its center and nowhere. We discovered that the universe seems to be flat. It not open, it is not closed, it is flat. If that doesn’t make any sense, you need to listen to the previous show because there’s no way I could give that an explanation. So now we want to know: “How big is it?” Does it go on forever or is it finite in scale? How much of it can we see?

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cool cant wait to listen to this show

ok I'm over thinking,and haven't finished the show yet, but... why aren't the photons that where fired 13bil light-year, and traveled 78 bil light-years to get here... didn't it go past the speed of light to get here... ouch! stop it hurts!! =p

ok guys question from Megan. Could the CMBR be the out edge of like a bubble, and beyond that is nothing void?

the cmbr is the heat left over from the BB .. its everywhere...

beyond our horizon is like where they used to draw dragons on old maps

ie we dont know but for sure there is alot more of what we see around us and a lot else besides....and as you know void can cause all sorts of problems ! lol

Hi Megan

Good question. One of the big problems I think, is that if the CMBR was the edge of the universe (instead of just the limit we can see because of the age of the universe and the speed of light), we would have to infer Earth is at the centre of that universe. The Cosmological Principle (and the Copernican Principle) argue that we should not consider Earth to occupy a special place in the Universe (however special Earth is to us!).

Every time in history that people thought we were the centre of the Universe, it turned out they were wrong!

I loved this show by the way!

"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."
Douglas Adams, The Hitchhiker's Guide to the Galaxy

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If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

This is how I understand it:

The photon has travelled 13.7 billion lightyears to get here, but the place the photon started from has since been carried away by the expanding universe, and is now 78 billion lightyears away.

It also means when the photon started out, that place was a lot closer than 13.7 billion lightyears to this place - that original distance has expanded to 13.7 billion lightyears in the meanwhile. (And, of course, the Earth wasn't even here then, just some hydrogen gas floating about that would eventually become the Milky Way, Earth, people... just in time for that photon to hit WMAP. Weird huh?)

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

Towards the end of this episode you guys talk about the observable universe, and it being 1/100th cubed. Should this not be one millionth instead of one ten thousandth?

Thanks,
Guustaaf

So, a question for a future episode of Astronomy Cast. It's been rattling around for a while but episode 79 served as a good motivator for me to ask it...

Considering how little we can actually measure and study of the universe, apparently our best guess seems to be the cube root of very little, how can we make such remarkably intricate theories about the first few slivers of a nanosecond after the Big Bang? On one hand it sure seems like a lot of recent evidence suggests we may have mistaken the elephant's leg for a tree.

I mean, remarkable details of Big Bang theory seem pretty widely accepted, such as the temperature at each instant, the primitive particle and force interactions, etc, and then, almost as an afterthought as we review our notes, we stumble on inflation, dark matter and dark energy?

I get the feeling it's as if, in the dark, we've accidentally walked into the closet rather than the house, then lit a candle and crafted an entire theory of residential construction based on an exhaustive examination of the clothes rod.

I love the podcast. Thanks for all the hard work. It's an exciting and amazing time to be paying attention to cosmology, eh? (but, then, when isn't?)

I just hope we're all around for the next Newton or Einstein... and I hope our world hasn't become too greedy, and too venal, and too shallow, for minds such as theirs. I'm sure it is a very beautiful tree...

But I like elephants too.

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

I was wondering the same thing when I listened to this part of the show:
100 squared = 10.000
100 cubed = 1.000.000

Yes, we definitely made a math error there.

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Fraser Cain
Publisher
Universe Today - Free space news delivered by email every weekday.

I am new the the Astromony Cast forum, so let me first add to the chorus that the podcast is absolutely terrific. I look forward to each week's "episode" for the commute.

I have a question about the metaphor that everyone uses concerning the expanding universe -- that we are on the surface of the balloon.

So suppose I am on the surface and I take out my ruler and measure an object one foot away. To test this, I nail (OK tape, its a balloon after all) the ruler at point A and at point B. One foot. The balloon expands. Next time I look -- its still one foot. The balloon expanded, but so did the ruler. Relative to my world, on the surface of the balloon, the measurement did not change.

I think in the last episode Dr. Gay said that gravity and chemistry keep mass together while the universe expands around things. This is difficult to understand. It seems to be saying that "mass" exists independent of "space." That one can add "space" without making the mass any bigger.

Can someone explain this to a dense non-science type such as myself.

Hi MTaylor,

Welcome to the forum.

Some people add to the balloon analogy.

Imagine you have attached coins to the balloon - as the balloon expands, the distance between the coins stretches, but the coins remain the same size. The coins are analogous to galaxies, or more accurately clusters of galaxies.

The universe expands, but only on the largest scales where expansion overwhelms gravity, electromagnetism and the nuclear forces that binds us, earth, and galaxies together.

It's said that if you clipped a very (very!) long tape measure to a distant galaxy, waited a while then wound it back in, your tape measure would be longer when you were done.

Nature hasn't provided long tape measures, but it has provided light, and light is observed to stretch between distant galaxies (red-shift).

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

Thanks Steve, but I am still confused.

Granted if one attached an object to the balloon, it would not expand while the balloon did. But if I understand the metaphor, the surface of the balloon is the two-dimensional substitute for the 3 dimensional world in which we live. We are to suppose that we are two dimensional beings living "in" the surface, not "on" it. There is nothing "outside" or "on" the surface of the balloon, unless it is a 4th or 5th dimensional object.

Sorry if this is taking a metaphor to far, but its always bothered me.

Sorry, had another thought. What if its not space that getting bigger, but time getting slower. You never hear about time. Suppose that the farther you get away from here, the slower time is. That would explain the appearance that the universe was expanding and red shifting -- wouldn't it?

lol... that is a metaphor too far. You'll need to pretend the coins and the surface of the balloon are in the same dimension, while not forgetting we have 'subtracted' a dimension from our 3d reality (which you obviously have a good handle on from the rest of your post).

You'll probably come across another common analogy that places ants on the 2d surface - same thing applies, the idea is to imagine the ants exist in the same dimension, not the next higher dimension they occupy in reality.

Invasion of the Fifth Dimension Ants!

You don't happen to have Spielbergs number?

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If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

That's a great point. Time is the 4th dimension of spacetime of course, and the metaphors so far have not included time.

I'm fairly sure time 'slowing down' would not have the effect you describe, I'm not even sure it can (slow down that is, aside from relativistic effects which I think are quite a different beast).

I usually try to imagine 4d spacetime as a 3d loaf (one dimension subtracted again) - time being 'slices' of the loaf. Relativity means you can slice the loaf at different angles, so that different angled slices will include different events. The slices are always ordered from back to front (past to future - the arrow of time) due to increasing entropy (or disorder) in the universe. Then my brain melts.

Other than that, someone else might be able to help. Or you could post your question at Q&A, some of the folks over there are pretty damn smart. It's a great question, you're bound to get some great replies.

http://www.bautforum.com/questions-answers/

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If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

Thanks again. BTW. I read this explantion for the time dimension: time is the distance from the center of the balloon to the surface. I find this a useful metaphor because there is no "direction" as such to time, but for the ants on the surface, it always pushes outward.

I do not believe the time was that dimension inside the balloon analogy - it was a fourth spatial dimension. I just listened to the followup Q & A show and that reinforces this view.

The current thinking is there is probably 11 or more dimensions to the universe(s). But for the discussion on the shape and size of this universe, I think we can stick with three we experience, at least extra spatial dimension for the curvature of space in a way we cannot perceive and then one for time.

And, yes, this trilogy on the shape, size, and center of the universe is one of my favorites. I am almost done with the current Astronomy Cast! It is sooooo kwel - one of the best finds on the Net that I have heard in years!

I promise to donate right after I recover from the bill I have to pay to the warlords on April 15th.