expanding universe

The non amateur stuff. Hawking, black holes, that sort of thing

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cowait
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Post by cowait »

hi joe,

Reading your reply again. With regard to the amount of matter etc. I can see what you mean by the calculations being based on density and so on , and if there were more galaxies there would be simply more space to house them all. But, if there is for arguments sake, 100 times more universe outside the "visible bubble" then I suppose there would be 100 times the number of galaxies and, by extension, 100 times the mass of what we can see. On the other hand if there is 1 000 000 times more outside what we can see then presumably there would be 1 000 000 times the mass. Maybe all we can see is simply all there is.

Either way how would we know?

Cowait
joe
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Post by joe »

Hi Cowait,

There could very well be 1 million times more galaxies outside of the visible universe. And you might not be far wrong if you were to multiply that figure again by 1 million. We may never know. Also remember that when we look at something 12 billion light years away we look at it as it was 12 billion years ago (and there lies one of the fantastic delights of cosmology). We cannot look to the "edge" of the universe and see it as it is now. We deduce (infer??) what the density of the universe is from what we see around us. And of course we now know that actual visible matter, the galaxies, make up about 4% or 5% or something ridiculous like that. Most of the stuff in the universe is stuff that we cannot see.

regards,
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
Cliff
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Post by Cliff »

Dear al including Kaustav
Kaustav it seems I caught you up reading Singh's BIG BANG. But I suppose that's the advantage of being retired, even though I am a very slow reader!
With regards to your comment about what happens when the accelerating expanding Universe reaches the speed of light, well funnily enough I think a "New Scientist" reviewer in New Scientist said he was surprised that Singh's BiG Bang really only really gets up to 1992, cosmological discoveries after that only being a sort of afterthought. But I still thought the BIG BANG a pretty good read.
Best of luck from Cliff
Kaustav
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Reading time

Post by Kaustav »

Hey Cliff! Welcome back :-)
I only get to read on The Tube or weekends (sometimes) so it takes me ages to finish books... sometimes I welcome morning delays in service as I can sit cosy in the warm carriage and read! LOL I think the point of Big Bang was to appeal to the layman and actually show the process of science and discovery, evolution of theories and how and why the evolution happens and why science is important. Astronomy, in the context of Singh's books, was a great vehicle to demonstrate these concepts.

Another super book I recently read, Cliff, is Einstein's Cosmos by Michio Kaku. It's a very nice alternative biography on the great man. Quite different to all the other biogs about Eistein before this one. Incidentally, Kaku is giving a lecture on Einstein and his theories at the Royal Institute at some point in Jan 2005. Should be a good lecture.

Kaustav
Kaustav Bhattacharya
>> http://kaustav.uk.com/unisphere/ - An online magazine about Astronomy, Science, Social Media and Society.
>> Follow me on Twitter @jupiterorbit
Cliff
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Post by Cliff »

Dear Kaustav
Thanks for the reply. As I said I am a slow reader, and I have lots of astronomy books some of which I am ashamed to say I have hardly started reading. However, much as I find cosmology a fascinating subject, so far as I am concerned cosmology is only one aspect of astronomy. I find many of the other aspects just as fascinating particularly those things my own observations directly relate to. I particularly like reading books about practical observing for amateurs -anything from the Sun, the moon, planets, double stars, variable stars, galaxies.supernovae, gravitational lenses. I am a Jack of all astronomy Master of " NON". And no apologies for shouting.
Having said that I once went to a talk by a well known professional cosmologist and he showed a picture of a galaxy which he said was M31 but I do not think many amateur astronomers would have agreed with him. He actually showed the pic a second time and made the same mistake so I do not think it was a slip of the tongue - I could hardly believe it, nor could some of my friends in the audience.
Best wishes from the Old Codger Cliff,
paulestar
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Post by paulestar »

On the commute home last night I got to thinking about the expansion of the universe:

Going back to the sponge cake analogy , I can see that both matter, and the actual space between matter, is expanding (I don’t know about anti-matter so I’ll bury my head in the sand about that for the moment...). So in absolute terms, if everything is expanding, does that mean that a 1m distance tomorrow is larger than it is today? Clearly in relative terms, 1m stays the same – my scope is still 0.114m – same as when I first got it! b But relative to some sort of absolute measurement, has the size of my scope changed?

Going a step further...(I'm taking edfinitions from http://physics.nist.gov/cuu/Units/current.html )

Prior to 1983, “the meter was intended to equal 10-7 or one ten-millionth of the length of the meridian through Paris from pole to the equatorâ€
Paul
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joe
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Post by joe »

Paul,

The aperture of your telescope stays the same because the electromagnetic force, the strong and the weak nuclear forces that hold the particles and molecules together are far stronger than the force that causes the expansion of space. Similarly the planets do not move further apart due to expansion and even the space between stars and galaxies is not affected by expansion because gravity is dominant there. It is only the vast spaces beween clusters of galaxies where there is very little matter and therefore no competing forces that expansion comes into play. There is obviously a lot of space there so expansion is dominant overall in the universe at the moment. So no funny stuff going on with time. The metre is still a metre and light takes the same amount of time to travel that distance.

Regards,
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
paulestar
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Post by paulestar »

Thanks Joe! What you say makes sense!
Paul
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cowait
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Post by cowait »

Hi again Joe,

But what about light that might be travelling through those vast voids between clusters of galaxies? If that space is expanding and the light is passing through what happens? Does the light carry on regardless of the expansion? And what if the expansion were to be at a rate greater than light speed?
I am only asking because I can't get my head round it at all.
joe
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Post by joe »

Hi cowait,

Light is stretched along with the expansion. For example the Cosmic Background Radiation that started out in the visual part of the spectrum has been stretched to micro wave length over the last 13 billion years. The expansion rate is 70km/s/Mparsec (Hubble Constant) so it's a great deal slower than the speed of light in our reference frame, but at greater distances it can easily exceed light speed from our perspective.

Regards,
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
joe
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Post by joe »

I've got a minute so I will add that at great distances space is moving away from us faster than the speed of light (70+70+70+70....). The light filling that space is still travelling at c locally but, similar to a black hole, this light and indeed space, cannot be seen by us and we are therefore surrounded by the inverse of a black hole I suppose. A black circumference....for want of a better name.

EEK :shock:
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Cliff
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Post by Cliff »

Dear Joie
I believe you!
But only 'cause I can't prove you wrong.
Which makes me feel quite a grumpy old codger Cliff
joe
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Post by joe »

Cliff,

Have a go. After all I'm only repeating what I've read. I can't say all of this is true but we could all have an enriching debate. 8) And perhaps offload some grumpiness.

Regards,
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
Cliff
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Post by Cliff »

Dear Joe and Kaustav
Joe; I like to think I am a clever clogs and of course I am,but I can't, not even me can prove you wrong in this instance. My mind boggles about the most aspects of cosmology. I think its great even if I do not understand it. So far as I am concerned science is very important and one of the things that attracts me to astronomy. It offers other attractions as well of course.
Kaustav, I love disagreeing with you whenever I can (and with everyone else of course). I have never as yet read any of Professor Miko KK..'s books. Indeed, as you see, I always get his name mixed up. However, I recently saw him on a TV programme and he demonstrated the dreaded fast spinning star himself on ice skates. I have to say he looked a very competent skater, I was really impressed. I hope to try reading the book you suggested.
Best wishes from the Grumpy old codger Cliff
Cliff
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Post by Cliff »

Dear Kaustav and Joe et al
I visited our local Waterstones yesterday and browsed the astronomy books. I noticed one I had never seen before by M.Kaku, I think it is called "Parallel Universes". I had a quick flick through and even considered the possibility of buying it, but decided to refrain from doing so. It certainly looked interesting but some of the subject matter looked a little bit hairy-scary. anyway I acted with resptraint at least for the time being. However, it did encourage me to think about reading a bit more about cosmology. This morning I pulled "Teach Yourself Cosmology" off our bookshelf and had another read. When I fully understand that book if I can pluck up the courage I might try Kaku's new book.
Incidentally I do think "Teach Yourself Cosmology" is a very good read although my copy was published in 1999, I wonder if it has been updated, cutting edge knowledge is advancing at a rapid rate.
I just read a bit more of John Gribin's "Deep Simplicity", I cannot decide whether or not I really like this particular book?
Best wishes from the Grumpy old Codger Cliff. Feeling very grumpy again having set up my telescope earlier tonight and then dismantled it without seeing a sausage except for cloud!
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