But if the universe is made up of far more empty space than solid stuff, then can’t you get a straight line of sight between any two points and look directly at the opposite side ?

Again…the “expanding balloon” is just the region that you, personally, can see. Someone in one of those far-distant galaxies in the picture wouldn’t see themselves as on the “edge” of anything, they would see basically the same as what you see – an expanding sphere of space around them dotted randomly with other galaxies.

The universe itself doesn’t have an edge.

There may be galaxies beyond the ‘edge’ of what we can see, but we’ll never know anything about them so it’s moot, they may as well not be there.

Which one is Tom Cruise’s home world ?.

The recent Horizon programmes, How Big, and How small is the universe explained “the observable universe” pretty well.

The empty space isn’t empty.

The empty space isn’t empty.

God’s hiding in there waiting to go ‘Boo!’ when we least expect it.

It’s not that galaxies are whizzing away from a central point, more that the space between them is being stretched.

Forgive me, I am a (very) simple person but fascinated by the images from Hubble.

Someone mentioned that the Big Bang didn’t happen in a single place, rather everywhere at the same time. But what went Bang? Surely there was something to go bang in the first place? Nothinghness doesn’t go ‘pop’…. does it?

Ow, ow, ow, ow, ow.

http://www.newscientist.com/blogs/nstv/2011/07/how-the-universe-appeared-from-nothing.html

The universe was very tiny to begin with. I’m quoting here:

Lemonick and Nash in a popular article for Time describe inflation as an “amendment to the original Big Bang” as follows: “when the universe was less than a billionth of a billionth of a billionth of a second old, it briefly went through a period of superchanged expansion, ballooning from the size of a proton to the size of a grapegruit (and thus expanding at many, many times the speed of light).”

But—-if it was possible for anyone to be around at the time and measure it, would they have thought the universe was “the size of a grapefruit”? -or would the massive curvature of spacetime have made the ruler, the observer and everything else correspondingly tiny – so to the observer, the universe always appears the same size?

But what went Bang? Surely there was something to go bang in the first place? Nothinghness doesn’t go ‘pop’…. does it?

Apparently it did.

You can “rewind the tape” as it were to the very earliest moments using known physics but the actual trigger itself is down to speculation at varying degrees of wildness – quantum fluctuations, oscillating cycles of big bangs and crunches, spawning from singularities in “parent” universes, collisions between higher-dimensional braneworlds, etc etc etc. Take your pick 🙂

But—-if it was possible for anyone to be around at the time and measure it, would they have thought the universe was “the size of a grapefruit”?

Yes, but only in the sense the “grapefruit” was the region that they, personally, would have had access to.

That grapefruit has now expanded to the visible universe that we can see, 13 billion light-years in every direction around us…but the “edge” of it isn’t a physical boundary, and never was.

“when the universe was less than a billionth of a billionth of a billionth of a second old, it briefly went through a period of superchanged expansion, ballooning from the size of a proton to the size of a grapegruit

Now that makes no sense to me. How can it have had a physical size, if it was the entire universe? Every ruler in existence would also have been tiny.

If you are a stick man drawn on the balloon’s surface, it would always look the exact same size to you, surely?

Every ruler in existence would also have been tiny.

Napoleon was on the small side, I’ve read.

How can it have had a physical size, if it was the entire universe?

It.

Wasn’t

The.

Entire.

Universe.

…just the amount of it that a (very hypothetical) observer could have interacted with.

I reckon that if we fast forward a couple of hundred years, everything we think we know about the universe will turn out to be utter garbage.

Big Bang my arse.

Well, not quite. That is a 2d analogy of a 3d system. So in effect the galaxies are also spread out inside the balloon.

It’s a bit like.. ooh I dunno, a nail bomb.

Personally I was going to use the analogy of fruit in a cake, but a nail bomb works for me lol

I was also beaten to quantum fluctuations and collisions between membranes in higher dimensional space. I’m just wading through Cycles of Time by Roger Penrose, one of the original exponents of the big bang theory, which is his current view of the evolution(s) of the universe based on the laws of thermodynamics…. I think….

just the amount of it that a (very hypothetical) observer could have interacted with.

So you are saying you could have been outside our observable universe and seen the big bang from an external perspective?

Every ruler in existence would also have been tiny.

The question about rulers stretching in an expanding universe is actually a valid one.

The simple version is that matter at local scales (ie up to galactic clusters!) is bound together by forces (nuclear, electromagnetic, gravitational) that hold it together. The background expansion of space only becomes dominant on intergalactic scales.

The complicated answer involves full GR, which is above my pay grade 🙂

So you are saying you could have been outside our observable universe and seen the big bang from an external perspective?

Yes, you could have been outside our observable universe…in which case you would have seen (we assume) your own observable universe, which would have looked (we assume) much the same.

The background expansion of space only becomes dominant on intergalactic scales.

I thought of that, then I thought well if ST is consistent in the local environment ie on earth, and it’s expanding between, wouldn’t that make it more curved? And would that not make gravity stronger?

EDIT when I was at uni only the Astrophysics people did General Relativity. Maybe I should ask one of them 🙂

It’s all explained here,

[video]http://www.youtube.com/watch?v=buqtdpuZxvk[/video]

So you are saying you could have been outside our observable universe and seen the big bang from an external perspective?

yes but you’d have to run away very fast indeed to avoid getting hit in the head.

I think we just came a little bit closer to inventing the Total Perspective Vortex.

so heres a wee thought,
if in the future we invent a drive that allows us to travel faster than light, then go to a point in that XDF above, will we see ourselves now? as the light reflected from our spaceship took so long to get back to us…

Big Bang my arse.

Errr. You don’t want to rephrase that do you ?….

😯

I overheard a conversation between two blokes in the pub, discussing the universe & details of the higgs boson, implications of its existence etc.

They were clearly not physicists, but still managed to spout some marvellous ‘facts’ about something they clearly knew pretty much nothing about.

This thread reminds me a lot of that conversation 😀

Anybody on here an actual astro-physicist, or are we all just repeating theories from books and tv documentaries that we’ve bought into because it suits what we’d like to believe?

😉

My theory is there never was a Big Bang – the universe exists in an ‘aged’ state that just looks like it’s got loads of history. Bit like those jeans you can buy that look like they’ve already been worn/washed for years.

Anybody on here an actual astro-physicist,

Never let fact get in the way of a decent thread.. let me know when we get one.
😛

My theory is there never was a Big Bang – the universe exists in an ‘aged’ state that just looks like it’s got loads of history. Bit like those jeans you can buy that look like they’ve already been worn/washed for years.

God stonewashed the galaxies?

Going back to the image from Hubble, they could have saved a lot of time, effort and money by simply asking an eight year old to ‘draw space’.

About the pre-aged universe comment above… If you were able to create anything you could imagine, and you wanted to create say… a tree, would you create a seed first when you could create a full grown ‘ready aged’ tree? if you could create any animal, would you create an embrio, or create a fully developed specimen, ‘pre aged’. If you could, why not?

*see’s direction thread is going and wanders off disappointed*

Solo – nah I’ll keep it as it is. I did check the capitalisation a few times though.

looks like we are just a stones throw away from the Total Perspective Vortex

[video]http://www.youtube.com/watch?v=kSnJl7B_TVs[/video]

Anybody on here an actual astro-physicist, or are we all just repeating theories from books and tv documentaries that we’ve bought into because it suits what we’d like to believe?

I have a degree in Physics, I did some astro but sadly no general relativity. A lot of my mates did though, I was always jealous. But not jealous enough to put in the extra work 🙂

I still don’t get it. So is the general theory that all all galaxies in the visible part of the universe expanding away from each other, or from a point?

Different question, when people are referring to ‘The Universe’ do they mean what we can see, or in it’s never ending, total entirety?

Different again, is the big bang seen as what created the never ending entirety, or just the bit we can see

And again how the hell does nothing go pop?

The universe is all expanding away from itself, like the dots on the balloon surface.

Different again, is the big bang seen as what created the never ending entirety, or just the bit we can see

Er, well who knows? The bit we can’t see is undetectable. We can never know about it, because no information at all can reach us from it.

So that’d make the ‘universe’ as normally referred, the visible bit only.

I will admit, my mind hurts a bit when I try to think about this.

Different again, is the big bang seen as what created the never ending entirety, or just the bit we can see

Er, well who knows? The bit we can’t see is undetectable. We can never know about it, because no information at all can reach us from it.

True. On the other hand, one thing we *can* say is that the bit we can see seems to have pretty consistent properties all the way across, and there’s nothing particularly special about where we happen to be in it.

So although we can never see “elsewhere”, there’s also no strong reason (as yet) to suspect “elsewhere” is actually any different.

So that’d make the ‘universe’ as normally referred, the visible bit only.

Most of the time, yes.

(Another general-purpose physics degree here!)

Serious point here. Anyone who wants to learn more about this in a way that is relatively easy to follow should check out Khan Academy

It’s a brilliant learning resource and was designed for high school children and under grads to supplement their learning. The section on cosmology is particularly good.

I devoured that section in a week of commuting as it works on the iPhone via YouTube.

Halfway through an OU Physics degree, just started the level 3 modules, with a bent towards astrophysics and Quantum Mechanicas

transapp – Member
I still don’t get it. So is the general theory that all all galaxies in the visible part of the universe expanding away from each other, or from a point?

Its the space that’s expanding so everything is moving away from everything else but not from a specific point, as has been said before its like dots on the surface of a balloon or fruit in a cake (I love cake). The velocity of the recession of a galaxy, from our reference frame cam be measured by the red shift of its spectrum, which is proportional to its distance from Earth, and some magic maths giving you a value of (Km/s)/Mpc

This holds true when observing distant galaxies in isolation. The view changes when you look at gravitationaly bound structures such as galaxy clusters, in which case you can see colliding galaxies which clearly aren’t moving apart.

Not to worry anyone but Andromeda (M31) will hit us in about 4 billion years …. and if its clear tonight you will be able to see M31 though a pair of binoculars…

I can thoroughly recommend this for any budding amateur cosmologists. Takes you from the first guy who measured the earth’s circumference to the current state of knowledge about the big bang via Gallileo, Copernicus, Keppler, Newton, Einstein etc

+1 upthedowns an excellent read

Cosmos by Carl Sagan is also worth a read though its a bit dated now