View Full Version here: : How big is the Universe

06-08-2009, 06:42 PM
I read it was 160 billion light years and even that was pointed out to be too small...so what is the excepted view...
ANy ideas please... and is there an "outside"?

06-08-2009, 07:42 PM
Wicky says 93 billion light years diameter.

06-08-2009, 07:43 PM
I'll say Hi Alex, ;) but and answer to your question is just beyond me, if 160 billion is still to small, than I couldn't even come up with a guess.

Leon :thumbsup:

06-08-2009, 07:58 PM
Hi Leon good to hear from you ..are you saying you have not been to the edge yet:D... oh well maybe after a few more trips around the place you can take a look near the edge.

Yes what ever numbers are correct I think it must be a rather huge place.


06-08-2009, 08:02 PM
Hi Alex.

What a conundrum! Is the Universe infinite in size? Who knows.
The age of the Universe is supposedly around 13.73 billion years.
I'm guessing we are talking about the observable Universe. How do they come up with the figure of 93 billion light years diameter (or a distance of 46.5 billion light years)? Pure guesstimation.
We don't know how expansion has varied over time and therefore cannot possibly calculate an exact size for the observable horizon.
Then there is the cosmic event horizon at 16 billion light years. Supposedly, light being emitted now from galaxies this far out will never reach us due to their speed of recession.

Regards, Rob

06-08-2009, 08:16 PM
Depends on what you define as being the "Universe". If you're talking about the Local Universe (Local Bubble, Hubble Domain...whatever you want to call it), then it's about 95 billion light years across. Now you're probably wondering, yeah, but why do they say it's 13.7 billion years since the Big Bang and yet it's so much bigger than 13.7 billion light years??. Well, it's a matter of what you define as a distance. The value of 13.7 billion is the number of years the light has taken to travel from those objects we see close to the time of the Bang, to us now. That is, the light travel time. The actual physical distance to those objects as they are now, is an entirely different matter. Due to the way the expansion occurs, those objects are in fact further away than the light travel time seems to indicate. In fact, the distance the object is at now is greater than the light travel time multiplied by the velocity of light, c....or thereabouts. This link should explain it fully for anyone wanting to know how far away are they.....FAQ Cosmology (http://www.astro.ucla.edu/%7Ewright/cosmology_faq.html#ct2)

So, if we mean the Universe as a whole, and not just the Local Bubble, what do we have to consider when talking about the size of the Universe??. The main thing we have to consider is the apparent flatness of the topology (or shape), the Universe presents to our observations. Whilst we can only see to the "event" horizon of the Local Bubble i.e. where the velocity of recession approaches and exceeds the speed of light (c), spacetime itself is much, much larger. Think of it like standing on the Earth and looking out to the horizon. You can only see 10 miles standing at sea level because of the curvature of the planet. That 10 miles is your horizon distance. Now, there's a lot more Earth beyond that we can't see and it's the same with the Universe. Just how big it is we don't really know, only that it's vastly bigger. Because the Universe we see is exceptionally flat, the Universe would have to be at least 20 times as voluminous than the size of what we see. It's at least 70 billion light years in radius, and many figures quoted by the guys in the know (e.g Andre Linde), range from 160 billion upto many trillions of light years in radius.

My own opinion??.....it's most likely many, many trillions of light years across, given how flat the topology is and how finely balanced the critical density of the Universe seems to be with the other factors which govern it.

06-08-2009, 08:21 PM
I dont know but it can not be infinite under the Big Bang Theory that is for sure (I think) as you can not double a finite (as the original seed was finite)up and up so that it reaches infinite.. a trillion to the power of twenty seven trillion is still finite big but finite and you could take the result of that sum away from infinite and still be left with infinite.. infinite is neat and the prospect of an infinite Universe impossible to imagine...but if it is infinite possibilities are also infinite.. that would translate into a real possibility that everything is possible maybe...it is a wise man who can imagine a stick without ends and a circle does not cut it by the way.

I used to have great difficulty in accepting the size to age thing until I understood the concept of space expanding.. how can it be 160 billion light years if matter is limited to C and the age is 13 billion..one will come up with a Universe with a radius of 13 billion light years..but add space expansion and I can see the opportunity for those bigger than expected estimations.
I have been looking around the net and have not found two estimates the same so far.


06-08-2009, 08:26 PM
Wonderful post Carl... up to trillions even... I am starting to think maybe we are only part of a much larger creature..we may be its equivalent of germs..in fact I bet if we worked it out in such a relationship we would be smaller than germs are to us.

Great stuff for mind hurting.


06-08-2009, 08:27 PM

Well, there is a lot of uncertainty it seems. I read that we are fairly certain that it is at least about 93 billion light years across, which is the volume of observable things.

So even though the age of the universe is about 13.7 billion years, the edge of the observable part is 46.5 billion light years away. Boggling.

However space-time beyond that might be infinite, we don't know. The recent discovery that the expansion of the universe is accelerating has thrown a big spanner in the theory of it all, we don't know just what is responsible.

There is no evidence that the edge of what we can see corresponds to the edge of what exists (if there is any). That 160 billion light year figure was the result of a widely reported theory which is now thought to be incorrect.

I feel like a stunned mullet every time I try to understand it all.


06-08-2009, 08:34 PM
It can be infinite. General Relativity (and we are not even sure if that is correct over mega-cosmological distances since we have not yet been able to test it to that degree) places no limit on the expansion of space-time.

That is how we can observe stuff over 46 billion light years away even though we think the age of it is less than 14 billion years.

We really need to be able to detect gravity waves (as yet theoretical) before we can take the next step to understanding all this.


06-08-2009, 08:46 PM
Here's something which will make you heads hurt even more:D

Considering that in order to explain the Standard Model as it is, in terms of String Theory and Supersymmetry, we need 11 dimensions in spacetime. Then the dimensions we live in and experience are just a tiny fraction of what really exists. In fact, according to theory, the Universe we inhabit is nothing more than the surface of a higher dimensional object floating around in an even higher dimensional space (a space of all spaces....a superspace).

06-08-2009, 08:57 PM
Geoff said.....It can be infinite. General Relativity (and we are not even sure if that is correct over mega-cosmological distances since we have not yet been able to test it to that degree) places no limit on the expansion of space-time.

I think infinite means infinite and even though GR sets no limit something can not start azs finite and grow to infinite..or so I believe... double the Universe in size everday for a trillion years it is still a finite size and although huge still is not infinite... the way I understand it you can not add subtract or divide infinite and be left with anything greater or less than infinite ...
I read some stuff on infinite once and they say folk into it go crazy and I could understand why.


06-08-2009, 09:03 PM
that utube clip on the lecture at Berkley by David Gross mentioned super space and supersymetry and really it was a great overview I thought:thumbsup:.

06-08-2009, 09:10 PM
AND if finite what is on the outside:rolleyes: ... and GR will answer there is no outside I think so if there is no outside it must be infinite although inside it has a finite size:shrug:... mmm I think we all need a drink:whistle:

06-08-2009, 09:55 PM
There is no outside, from our perspective. Like I have mentioned in previous posts elsewhere, outside means outside of our spacetime and therefore bears no relation to our perceptions. We can't see it, nor can we access it with any technology we know of.

07-08-2009, 08:48 PM
Exactly, but it does not mean it is not accessible.

07-08-2009, 09:04 PM
True, but we have no idea of how to do it, or even if it's possible.

07-08-2009, 09:13 PM
Sure, but to deny possibility that sometime in the future the technology and the way we think will be able to see beyond our visible universe would be equal to denying that America exist. The history teaches us not to place limits on our understanding and our knowledge.

07-08-2009, 09:33 PM
I'm not denying any possibility, but it will probably be a very long time before we can do that....then again.

07-08-2009, 10:02 PM
Thatís one of few regrets I got of being old fart. That Iím unlikely to see man landing on Mars and to see that speed of light is no ultimate limit. To see that I would have to live another couple hundred years.

07-08-2009, 10:14 PM
At the rate they're going about it, I probably won't see them land on Mars, although I hope I do. So far as the invention of the warp drive goes, I wouldn't be so pessimistic. Give them another 50-100 years.

07-08-2009, 10:49 PM
Just ask the folks drinking fine wine in the restaurant at the end of the universe

Arthur, Ford, Trillian and Zaphod would know for sure the answer to your question

07-08-2009, 10:55 PM
I know it already.....42:P:D:D

07-08-2009, 11:03 PM
aaaah..but what was the question??????

07-08-2009, 11:05 PM
What is 6 times 7...or....how hot can a hotdog get when a hotdog's as hot as it gets??:P:P:D:D

07-08-2009, 11:11 PM
As I see it Ė if the speed of light is absolute limit Ė there is no point in anything at all. Humanity is doom to spend its time in our solar system. Such a limit implies also limit on our understanding of the Universe that we live in. Iím quite aware of what current theories and the technologies limits are. But if we accept those limits we may as well give up and take up religion instead of science. I do hold hope for mankind based on history that whatever the conventional thinking places the limits; there will be always individuals that will try to cross the limits. I got no scientific paper to refer to validate my conviction. I just know that in any ages there always have been men trying to reach for impossible. I just hope that humanity has not been too badly affected by political correctness and all that rubbish circulates today in the effort for masses to conform to the will of few. We have rise above all living things because our ability to question and to adapt. My believe in humanity success in reaching the stars and to survive until the end of Universe and maybe beyond of that is strong

07-08-2009, 11:26 PM

A lot more work needs to be done on this because there's many assumptions that have been made which will probably prove false. It's only because of our limited knowledge at present that we can't see beyond the problems. It will probably take some new form of physics.

There's to many "if's" being touted for and against, so I don't think they really know what to do with the physics as it is. For now, anything said for and/or against is pure speculation.

07-08-2009, 11:37 PM
If the Universe is expanding into existing space then the cosmological principle is violated.

Mathematically I would be able to define a "centre" of the Universe.
To account for the cosmological red shift data and observation that shows that the Universe is isotropic, I would have to place the Earth at the precise centre of the Universe.

Now that is too much of a coincidence.


07-08-2009, 11:42 PM
The flat earther's, religious fundamentalists, the Vatican (behind closed doors, though) and conspiracy theorists would love that:P:D:D

08-08-2009, 12:12 AM
Hell, Steven I never thought you would ever say IF. I'm sorry if I underestimated your abilities to think beyond of math.

08-08-2009, 12:31 AM
That definitely was not intension of me writing it. Although I consider myself as agnostic lately, it is only because I come to conclusion that Iím hypocrite if I say that Iím atheist. I do not believe in creator but it is only my conviction. I do not have proof. Therefore if I insist on being atheist without any proof I place myself on same level as creationist or any religious fanatic. Iím atheist by believe but agnostic because I really donít have proof for my conviction.

08-08-2009, 02:09 AM
Your backhander has as much subtlety as being hit by a semi-trailer.

At least I have the ability to think and not make judgements based on pure ignorance.

08-08-2009, 09:21 AM
I didn't write that in response to your posts. It was in response to Steven's...it was meant in jest:P:D

Peter Ward
08-08-2009, 09:46 AM
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, sorely missed)

08-08-2009, 09:58 AM
Not when you are powered with an Infinite Probability Drive.

08-08-2009, 10:04 AM
Yeah, but who wants to end up looking like a garbage can:P:D:D

Or a carrot, bunny rabbit, sofa, toilet brush..........:P:D

08-08-2009, 10:19 AM
Well I didn't say it was perfect.:D

08-08-2009, 11:50 AM
To answer your question in simple terms Alex, nobody knows :P
And as long as people are forced to think inside a certain norm (peer pressure and redicule) there will only be very slow progress and humanity will be long gone before the answer is known.


09-08-2009, 10:50 AM
Sorry to be late in thanking everyone for their input...but thank you all.
May I ask this...
If we have the Big Bang theory and observations consistent with it can they not extrapolate how big it must be by now with reasonable accuracy.

09-08-2009, 11:04 AM
Alex here is a reasonable doco on the infinite and other problems. It fails somewhat due to the tabloid type of treatment.

It is a 175MB FLV



09-08-2009, 11:05 AM
As an Atheist it is not your job to prove of dis-prove a proposition that
wasn't put forth by you, and why would you. The question is simply


09-08-2009, 12:23 PM
It depends on whether the accelerated expansion of the Universe has remained constant since the end of the Inflation era. (And that is assuming of course the acceleration started from that point of time.)

Since the Universe has expanded by a certain amount in the period of time it takes the light for distant objects to reach us a scale factor is introduced. The scale factor can only be reasonably accurate if the acceleration has stayed constant.

If the acceleration has varied with time then we have no way of accurately determining how large the observable Universe is.


09-08-2009, 01:22 PM

It would operate as a sort of Mother Nature's quarantine, wouldn't it?

That is why I don't believe in flying saucers. Little green men are out there somewhere, almost certainly I think, but they can't reach us (I hope).

As a whimsical variation I have given myself the shivers by reflecting that there are creatures like the Alien somewhere in the Universe. Whatever you can conceive it ought to exist somewhere in space-time.



09-08-2009, 03:30 PM
Thank you very much Bert now I have a reason to go into the office and use the fast net;)... I am on dial up at the moment that cracks along at anything up to 25 ks per sec


09-08-2009, 03:31 PM
Ah....but does it??. Just because one scientist comes up with an idea that everyone else fawns over and it happens to fit experimental evidence, so far, doesn't mean that it's cast in stone. Just because we can't do something doesn't mean that someone else can't.

The problem is that when something lies outside of an accepted scientific paradigm, and gets lumped in with the kooky quasi-religious side, scientists will ignore it for the most part. People will paraphrase Sagan by saying "extraordinary claims require extraordinary evidence"...and that is a load of crock. Scientists deal with a great number of things, including very cherished theories, that have even less to do with reality than ET or UFO's, yet are perfectly acceptable.

09-08-2009, 03:35 PM
Thank you Steven... and if the acceleration of the expansion is as suspected I guess that makes it harder again.