Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Corney & Michelle on 25/05/2008 09:37:31
-
Corney & Michelle asked the Naked Scientists:
The universe is expanding right. Where does it end??? Surely there must be an end to deep space, it can't just go on forever? My logic cannot comprehend that.
Thank you and best regards
Corney Gibson
Cape Town
South Africa
What do you think?
-
For there to be an edge, that implies there is something outside of the universe to have an edge with it. That may or may not be the case. We shall probably never know.
One would imagine that, if the Big Bang theory is correct and the universe started from a point, there must be an edge. However, it is possible that spacetime is curved in such a way as to preclude there being an edge as such. It may be that no matter which direction you travel in, and no matter how far or how fast, you will never get to an edge. There will seem to be as much universe around you in every direction as at your point of origin.
-
Welcome, C&M
This topic and its accompanying topic "What was before the Big Bang?", have been discussed a lot, for example, a recent thread
http://www.thenakedscientists.com/forum/index.php?topic=14416.0 (http://www.thenakedscientists.com/forum/index.php?topic=14416.0)
contains a lot of questions and thoughts related to your question.
Basically, there isn't a meaningful answer to the questions in everyday terms. You have to let go of a few 'obvious' ideas if you want to get your head around the problem.
Have a look through the above thread and get back to us!
But, before you do, consider where is the 'end' of a rubber band?
-
A rubber band may not have an end, but it does have a limit it can be expanded to before it snaps. Maybe the universe is going to snap :P
-
Everything that exists now does so on the edge of the universe in the time dimension.
That is, if you assume that the future hasn't already happened yet.
-
But when is 'now'?
The 'Now' that was just then is past and the 'now' I am anticipating is in the future.
As soon as I say "now", the event is already in the past.
It's worse than trying to grab hold of the soap in the bath.
-
Yup - 'now' is a tricky blighter to grab hold of.
"The Moving Finger writes; and, having writ,
Moves on: nor all thy Piety nor Wit
Shall lure it back to cancel half a Line,
Nor all thy Tears wash out a Word of it."
Omar Khayyám
Wonderful stuff.
It seems to me that 'now' is either a point on the time-line or a duration (length) along it. If it's a duration then it's probably the Planck Time unit long.
-
See? It's that Plancky thingy yet again. Little blighter gets everywhere.
-
Corney & Michelle
See what you've done. Just wind us up and point us in the right direction and off we go!
I prefer the bit about "a flask of wine, a loaf of bread and thou", from Omar Khayyám
Sounds more fun!
And the less accurate quote I remember was
"The Moving Finger writes; and, having writ,
Moves on: and writes another bit"
(Tony Hancock or somesuch.)
-
Corney & Michelle
See what you've done. Just wind us up and point us in the right direction and off we go!
I prefer the bit about "a flask of wine, a loaf of bread and thou", from Omar Khayyám
Sounds more fun!
And the less accurate quote I remember was
"The Moving Finger writes; and, having writ,
Moves on: and writes another bit"
(Tony Hancock or somesuch.)
haha love your work. thank you for the replies.
maybe this one will ring your bell? I read somewhere that there are more people alive today than have died in the history of the world. HUH??? My peanut can't get around that one. BUT WAIT!!! That led me to my actual question. What whould the combined age (+- of coarse) of all of us 6.5billion people on earth be?
thank you
corney (aka samurai)
-
OK but many of the sentences have run concurrently.
-
Corney & Michelle
See what you've done. Just wind us up and point us in the right direction and off we go!
I prefer the bit about "a flask of wine, a loaf of bread and thou", from Omar Khayyám
Sounds more fun!
And the less accurate quote I remember was
"The Moving Finger writes; and, having writ,
Moves on: and writes another bit"
(Tony Hancock or somesuch.)
haha love your work. thank you for the replies.
maybe this one will ring your bell? I read somewhere that there are more people alive today than have died in the history of the world. HUH??? My peanut can't get around that one. BUT WAIT!!! That led me to my actual question. What whould the combined age (+- of coarse) of all of us 6.5billion people on earth be?
thank you
corney (aka samurai)
I'm not sure what that has to do with the edge of the universe [???]
Maybe a mod would care to split it into a new topic.
-
Going back to the original question. It is quite possible for a universe of three dimensions to have a finite size but no edge. Consider the globe of our world this is the two dimensional analogue of it. You can walk in a straight line forever and you will not get to the edge of the world you will just keep on going round it.
The total gravity of a finite space bends space and extreme gravity can bend space so much that it closes in on itself. we see objects like this in our universe and call them black holes and cannot find out what goes on inside them. It is quite possible that our universe is physically closed like being inside a black hole and observers have been trying hard to detect if our universe is closed like this for about a century. Every so often people think that they have detected hints that it is closed. Some recent observations of the statistics of the blobs in the cosmic microwave background is the latest. but so far there is no incontravertable proof that we can see the size of the universe. but like the globe of the earth that does not mean that it has an edge. It is also quite probable that the size of our universe is many times greater than the farthest we can see as defined by their red shift and we can only ever see a tiny piece of a finite universe. This piece could be so tiny that there is just not enough information to ever know how big it really is.
Please note accelerating expansion does not necessarily mean that our universe does not have a finite size the expansion process is different from the geometry. it is also not essential that our universe is confined the local (out to the limits of red shift visibility) could have negative curvature and be saddle shaped and so look like it was essentially open so the universe we detect might still be open and of indefinite size from our observations.
Even having an open local geometry does not prevent a universe form being of a defined size because if the universe were toroidal like a bagel or a doughnut the local curvature would be negative.
My personal opinion is that the most likely shape for our whole universe is toroidal with one of the toroidal dimensions much smaller than the other a bit like a very long hosepipe connected together at the ends it is probably a bit distorted too however we can only see a tiny bit of the surface and may not even be able to detect the curvature of the smallest dimension of the width of the hose. let alone the length.
-
There is no edge, space is greated by Dark Energy as it expands.