| From: Danny Smith | 16/10/99
0:01:44 |
| Subject: Space | post id:
103 |
| Dear Karl, I am in year 8 and I am doing an assignment for Physics on the universe and I was wondering how big space is. From, Danny | |
| From: steve(primus) | 16/10/99
2:40:33 |
| Subject: re: Space | post id:
133 |
| The Hitch Hiker's Guide to the
Galaxy is a wholly remarkable book. It has been compiled and recompiled many times over many years and under many different editorships. It contains contributions from countless numbers of travellers and researchers. The introduction begins like this: 'Space,' it says,"is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean you may think it is a long way down the road to the chemist, but that's just peanuts to space. Listen.... and so on. (After a while the style settles down a bit)... ...To be fair though, when confronted by the sheer enormity of the distance between the stars, better minds than the ones responsible for the Guide's introduction have faltered ...The simple truth is that interstellar distances will not fit into the human imagination. Even light, which travels so fast that it takes most races thousands of years to realise that it travels at all, takes time to journey between the stars. It takes eight minutes to journey from the star Sol to the place where the Earth used to be, and four years more to arrive at Sol's nearest stellar neighbour, Alpha Proxima. For light to reach the other side of the Galaxy, for it to reach Damogran for instance, takes rather longer: five hundred thousand years. The record for hitch hiking this distance is just under five years, but you don't get to see much on the way. ---From The Hitch Hiker's Guide to the Galaxy by Douglas Adams | |
| From: Grantley | 16/10/99
7:18:18 |
| Subject: re: Space | post id:
135 |
| According to the big bang theory
the ubiverse is about 15 billion years old. If, since then, it has been
expanding at the speed of light then it is 30 billion light years
across. | |
| From: Gus | 16/10/99
11:48:30 |
| Subject: re: Space | post id:
151 |
| Danny, the Universe is
really big. Huge even. Distances on Earth are measured in metres and kilometres. The Moon is around 384,000 km from the Earth. The Sun is about 150 million kilometres away. After that, it becomes awkward to measure distances in kilometres because the numbers get too big. Astronomers use a distance called a light year to measure distances to stars and galaxies. A light year is the distance that light travels in a year. Light travels 300 000 km each second, and there are around 31 500 000 seconds in a year, so a light year is about 9 460 500 000 000 kilometres. Sometimes they use an even larger measure called a parsec which is 3.26 light years. The nearest star (other than the Sun) to Earth is Proxima Centauri, and it is about 4.3 light years away (41 000 000 000 000 km). The Solar system is part of the Galaxy. The Galaxy is a disk shape that is 100 000 light years across and has a bulge in the middle about 10 000 light years thick. There are hundreds of millions of stars in the Galaxy. There are millions of galaxies that we can see outside of our own. The Andromeda galaxy is about 1 000 000 parsecs (3 260 000 light years) away but is part of the same group of galaxies as ours. The furthest objects we can see are about 15 000 million light years away, that's around: 142 000 000 000 000 000 000 000 km away. OK, so that's really huge, but we can only see bits of the Universe that light has had time to reach us from. Current thinking says that the Universe is about 15 000 million years old, so the furthest visible objects are 15 000 million light years away. There may be much more of the Universe that is further away than that, but we cannot see it because the light from those galaxies and stars hasn't got here yet. I hope this helps. | |
| From: Gus | 16/10/99
11:57:56 |
| Subject: re: Space | post id:
154 |
| Now.. someone is surely going to
ponder the question.. whats outside our universe?!? im thinking lots and
lots of space. lol.:--->0) | |
| From: Grantley | 16/10/99
13:58:23 |
| Subject: re: Space | post id:
169 |
| We cannot know what is beyond the
known universe since we have no proof (absence of evidence is not evidence
of absence). But we can theorise (or is it
philosophise). | |
| From: Grantley | 16/10/99
17:47:38 |
| Subject: re: Space | post id:
249 |
According to the big bang theory the ubiverse is about 15 billion years old. If, since then, it has been expanding at the speed of light then it is 30 billion light years across. Oooooooo... err, no. :o) You can say that the visible universe (ie that portion of the universe which is visible to you here and now) has a horizon at radius 15billion light years (or so). This is because light has only had 15 billion years to reach you from the furthest corners. But the expansion of the universe is not limited to light speed so you can't imply an absolute size from this. Consider the situation where I stand on a small blue green planet orbiting a yellowish sun in a galaxy a million light years from you. My visible universe also has a radius of 15BLY too, doesn't it? Or did you think perhaps that the distance from me to the edge of the universe in a direction opposite you was only 15BLY minus one million LY??? That kind of thinking would imply that we are at the centre of the universe - an idea that has lost favour since Gallileo (or so). How big is the universe? Perhaps only God herself knows. Hope this helps! Chris | |
| From: Grantley | 16/10/99
17:58:25 |
| Subject: re: Space | post id:
251 |
Now.. someone is surely going to ponder the question.. whats outside our universe?!? im thinking lots and lots of space. Nope. Space and time exist inside the universe - there are no space-time paths which lead outside the universe, that's a contradiction by definition. There could be other pockets of space and time outside our universe, but they're certainly not continuous with our universe (so they must for the moment remain as philosophical questions in the land of the magic chicken). For Danny, I think the best description for someone at your age is "infinite". The universe goes on for ever. It goes as far as we can see, and then further. Try this exercise: draw a circle in pencil. Now take a pen and trace around your circle. You could trace around and around forever because a circle doesn't start or end. Space is a bit like that, you could fly off in one direction and literally fly forever! Hope this helps! Chris | |
| From: Grantley | 16/10/99
19:52:41 |
| Subject: re: Space | post id:
304 |
| But the expansion of the universe
is not limited to light speed so you can't imply an absolute size from
this. Why isnt the expansion of the universe limited to light speed?. Tachyons are still only theoretical and not yet proven to exist so as far as practical science is concerned, the expansion of the universe is limited to light speed unless proven otherwise (according to Einstiens theories of relativity) | |
| From: Grantley | 16/10/99
20:17:28 |
| Subject: re: Space | post id:
307 |
| That kind of thinking would imply
that we are at the centre of the universe - an idea that has lost favour
since Gallileo (or so). Im not sure how to highlight text. In answer to avatars answer, no I dont think that we are the centre of the universe since the parts on the edge are expanding the fastest so therefore time is slower for that part of the universe, som therefore everypart of the universe thinks(??)(if it can) that it is the centre of the universe due to time dilation. | |
| From: Cam | 16/10/99
20:17:38 |
| Subject: re: Space | post id:
308 |
| what if space was finite and had
no boundaries? i read that in 'a breif history of time'. Wrap your head around THAT. Oh, could you please explain it to me? | |
| From: Grantley | 16/10/99
20:23:09 |
| Subject: re: Space | post id:
309 |
| Yes, ive read that a number of
times to. Im no Stephen Hawkins though. Stephen Hawkins also said that, as
a scientist he doesnt have to be right all the time. Time is a dimension
and can be curved like all dimensions. If it can be curved then it doesnt
need conventional boundaries (as in a mobius loop in 2D, 3D
topology) | |
| From: Cam | 16/10/99
21:00:05 |
| Subject: re: Space | post id:
312 |
| but space would have to be curved
along with time...or not? is there such a thing as an infinite curve? | |
| From: Cam | 17/10/99
16:13:14 |
| Subject: re: Space | post id:
465 |
| Why isnt
the expansion of the universe limited to light speed? Tachyons are still
only theoretical and not yet proven to exist so as far as practical
science is concerned, the expansion of the universe is limited to light
speed unless proven otherwise (according to Einstiens theories of
relativity) The expansion of the universe is not limited to light speed because the light speed limit only applies to things moving against the backdrop of spacetime. The expansion of the universe is not an expansion in space (to which the limit would apply), but an expansion of space, which is a completely different thing. In answer to avatars answer, no I dont think that we are the centre of the universe since the parts on the edge are expanding the fastest so therefore time is slower for that part of the universe, som therefore everypart of the universe thinks(??)(if it can) that it is the centre of the universe due to time dilation. Time dilation is a relative phenomenon produced either by relative motion or differences in the spacetime curvature between two points (i.e. differences in the gravitational "field"). It is largely irrelevant to the question of whether the universe has a centre. Our best current theory of the evolution of the universe is the big bang theory, which postulates an explosion of spacetime. Since the explosion is happening everywhere at once, there is no centre of the expansion, and hence no centre of the universe. What if space was finite and had no boundaries? i read that in 'a breif history of time'. Wrap your head around THAT. Oh, could you please explain it to me? The most common picture used to explain this idea is that of a balloon. Imagine a balloon with dots drawn on it to represent galaxies. The surface of the balloon represents the universe. This is an important point - the inside and ourside of the balloon are NOT part of the universe - only the surface is. Now, if you're restricted to travelling within the universe (i.e. on the surface of the balloon), you can travel as far as you like in any direction and never hit an edge or boundary. However, the surface area of the balloon is finite. Hence, the balloon surface is an example of a two dimensional finite but unbounded universe. Our universe may also be finite but unbounded in a higher dimension. The balloon analogy is also useful in explaining the lack of a centre to the universe. As the balloon is blown up, the dots representing the galaxies move further apart. However, none of the dots (and therefore no point in the universe) can be considered as being the centre of the expansion. but space would have to be curved along with time...or not? is there such a thing as an infinite curve? Relativity tells us that space and time can no longer be regarded as strictly separate entities. Instead, we must think about a single, four dimensional spacetime. Curvature in relativity theory refers to a particular property of this four dimensional spacetime. We don't perceive the curvature of spacetime directly. Rather, we see the effects of the curvature as apparent gravitational forces. JR PS It's Stephen Hawking. | |
| From: Cam | 21/10/99
1:33:31 |
| Subject: re: Space | post id:
1364 |
| Chris, James, would you be my
private tutors? just kidding that explanation for the eight year old stuck in my head i've just read some stuff about faraday, he said to the mathematician who......Maxwell! yeah, well, he said why can't i express it WITHOUT the mathematics? apparently, you just can't. I don't like that. | |
| From: View From Space | 21/10/99
2:28:19 |
| Subject: re: Space | post id:
1366 |
| Oh Chris (Avatar)! "There could be other pockets of space and time outside our universe, but they're certainly not continuous with our universe..." The hubris of scientists (avatars?). How can you even begin to express ballpark ideas about the universe, let alone "certainties". I think we should all go and stand in a room full of mirrors and take a long hard look at ourselves! We know bugger all about the universe, and until somone can nip out to the edge of the universe for a quick gander ("...yes I had a look through a little crack and a voice told me to bugger off and stop being nosey...") we will only be guessing. Or until our intergalactic neighbours finally pull in for a cup of tea, and tell us what they know. | |
| From: Dr. Ed G (Avatar) | 21/10/99
2:47:32 |
| Subject: re: Space | post id:
1369 |
| I don't think Chris is
arbitrarily makig assertions about the physical nature of uncharted parts
of the Universe, but making a logically correct observation of fact.
Something which is a contiguous part of something else cannot logically be
considered outside that something else. The point is that space is part of the Universe. If there is an spatial end of the Universe, the space there must either stop (don't ask me how it would do this) or fold back on itself (much more likely) by definition! If there is space beyond the limits of this Universe it must logically be disconnected from this Universe in an isolated part or more likely a entirely different Universe (since according to General Relativity the existence of space is contingent on the existence of matter). Any other way of looking at it is simply logically inconsistent (irrespective of the physical reality/state of the Universe). Soupie twist, Ed G.  | |
| From: Halogen Fisk | 21/10/99
8:49:38 |
| Subject: re: Space | post id:
1377 |
| Universe was once the word for
Everything. If there are other universes, or something 'outside' our universe, what is the collective word for all the stuff? | |
| From: View From Space | 21/10/99
12:02:10 |
| Subject: re: Space | post id:
1438 |
| Thanks for your answer, Soupie,
very eloquent. I understand that relativity insists that another
space/time paradigm must not be part of our universe. That's like saying
that oil and water must lay separate. I suppose the crux of the matter here is defining what is "our" universe, ie, contiguous, and what is not. Perhaps our universe is expanding as an "onion ring", in amongst an infinite amount of other onion ring universes, all expanding out from one common point. If this was the case, we would all be made of the same stuff, but emanating in a staggered fashion from the big bangs (kind of like a big reciprocating engine). The trick to exploring these universes would be to accelerate to meet the next outer ring, or descelerating to meet the next inner ring. | |
| From: Dr. Ed G (Avatar) | 21/10/99
20:49:40 |
| Subject: re: Space | post id:
1643 |
| If there are
other universes, or something 'outside' our universe, what is the
collective word for all the
stuff? Omniverse. | |
| From: Cam | 21/10/99
22:54:00 |
| Subject: re: Space | post id:
1666 |
| Wow An eight year old started this thread. It's probably been the most intelligent one I've read in days! kidding. I found a bad side to learning. The act of teaching someone something increases the entropy in the universe, when you consider the energy degradation from the teacher learning the information in the first place. | |