Further Expansion

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

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Further Expansion

Post by joe »

The expansion of the universe thread was perhaps tumbling into a dead end about God and although interesting, perhaps it needs a nudge back to astronomy, SO.....Cliff, since you have expressed doubts about certain aspects of the Big Bang Theory could I ask you to try and express what it is that you find troublesome so that we could discuss it in more detail? (If you feel like it)

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Post by Cliff »

Dear Joe et al
I apologise for mentioning god again. I think I am not a believer in god myself but to be fair on people who do believe in god, I think that as far as they are concerned it may be impossble to discuss such things as the Big Bang without including god in the equation. But taking a stance as a non beliver in god (although strictly speaking I think I really qualify as an agnostic) I will mention the following. Sorry to have been repetitive again there, and long winded.
When I was a youngster I was excited by the Big Bang theory.
Bare in mind my first astro books suggested M31 to be 750,000 another said 950,000 light years away. (Now it is said to be 2.2 million, 2.5 or 2.7 or I once read 2.9 million Light years away). My understanding of the Big Bang as a youngster was needless to say very simplistiic (indeed still is fairly simplistic even now).
Since those days the Big Bang issue has got very much more complicated.
Things like the Cosmic Background Radiation have been discoverd which tend to back up the Big Bang. Then there have been other discoveries such as the accelerating universe (based on distant supernova measurements). Things like inflation, dark matter and dark energy have been discovered or introduced introduced and I have difficulty in getting my head round the possibility of ordinary matter accounting for a small percentage of the "stuff" that apparently supposedly exists.
A few years ago I read about Mond theory - Modified Newtonian Dynamics. I think basically this theory suggests that gravitation cand be different in different parts of the universe. If I recall correctly the first article I read about MOND in Scientific American several years said that Mond could account for most of the problems (except for one) as well as the Big Bang but without needing things like Dark Matter ( when I read the article I do not think Dark Energy was even thought about).
I have not read much about Mond since but once farly recently it was mentioned in New Scientist I think, and it was suggested that although very few cosmologists accept Mond it still has many possible merits.
Although I am still a Big Bang fan, the way I read things. the Big Bang seems to get more and more into difficulties and needs more complicated devices to make it work. Having said that being a coward I tend to favour the Big Bang but sit on the fence ready to fall whichever way seems the softest landing.
Incidentally some people also believe in a so-called fractal universe?
They see young tiny galaxies being spawned off apparently larger ones and they do not accept that the redshifts of some cosmological objects in particular some quasars give a true indication of at least some objects distances.
Best wishes from the Grumpy Old Wittering Old Codger Cliff
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Post by joe »

I don't know much about MOND but it doesn't replace the Big Bang of course, it just modifies what might have happened afterwards. I think it says something about Newton's equation Force = Mass x Acceleration, a law that works where gravity is "strong", i.e. within the solar system. We assume that it works exactly the same everywhere but MOND says that inbetween stars or galaxies where the force of gravity is small, very small, then things change. Using F=ma to explain the rotation speeds of galaxies has led astronomers to conclude that there isn't enough visible matter to account for the speeds therefore there must be other dark matter. MOND proposes that there is no need for dark matter just a tweak of the "acceleration" in Newton's 2nd Law. This cannot be verified in the laboratory because gravity is too strong here. One would have to conduct experiments way outside the solar system.

MOND interferes with a very successful theory (not good) but Dark Matter has yet to be identified properly (not good either). Take your pick. Gravitational lensing is a reality (dark matter needed there) so I don't know how MOND explains that phenomenon.
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Post by Cliff »

Dear Joe
Thanks for your comments.
Having just said what I did, I am now quite happy to leave god out of my equations so as to speak and hope I will not mention god again, in the discussions. But for anyone else who believes in god I am happy to respect their ideas.
Reading what you just said I think you know at least as much about Mond as I do and probably more. Your mentioning the point that Mond might be iffy with respect to fitting in with gravitational lensing is interesting. When I mentioned that I read one particular thing Mond could not satisfactorily explain I do not think it was gravitational lensing, so that could be a second phenomena Mond finds awkward. I still cannot remember what the other thing was that seemed to get Mond into trouble. Perhaps it was gravitational lensing? But either way I am glad you mentioned it.
As I said before, I was wholly happy with the Big Bang initially. Then we got inflation needed then, Dark Matter and Dark Energy and I do now feel out of my depth.
However, I have always thought the idea that the speed of light and gravity may not be constant constants quite fascinating. (and in some respects fairly easy for someone like me with limited mathematcal knowledge to find possibly acceptable.)
Best wishes from the Grumpy Old Codger Cliff Meredith.
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Post by joe »

I have a funny feeling that MOND can be used to explain lensing although I've no idea how, so perhaps we are back down to one hurdle again. I'll have to try and find out.
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Post by Cliff »

Dear Joe
Dare I say it?
After our previous forum natter I had second thoughts ie perhaps the gravitational lensing problem was actually the snag with Mond that I could not remember? I am still not sure!
If as you think possible Mond does manage to cope with gravitational lensing as you think may be, it could be interesting ?
However, although I do not think I will properly understand the scientific technical arguments properly one way or the other, it will be interesting to see how things develope.
Cor blimey I think I managed to end a sentence without a question-mark. However, please do not think any of the above question-marks are there because I expect an answer from you, they are there just to illustrate my uncertainty on these issues generally.
Best wishes from the Grumpy Old Codger Cliff
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Post by davep »

http://en.wikipedia.org/wiki/Modified_N ... Criticisms might interest you two if you've not looked already. It mentions (although has no link to) TeVeS -- a version of MOND that predicts gravitational lensing.

EDIT: http://arxiv.org/abs/astro-ph/0502222 turned up while doing a search for TeVeS. Way over my head but might interest anyone with a good understanding of this stuff.
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Post by joe »

Thanks for those Dave. A tad complicated I would say :?

I think the problem with MOND is that it has no physical or empirical foundation, for want of a better description. It seems to be a shot in the dark. A clever one though. Dark matter is not quite in the dark (Har Har), it is something that can be tested for, although with limited success so far. That's not to say MOND is a complete load of tosh, far from it, lots of people seem to take it very seriously but it doesn't have the back up of 3000-4000 years of observations. Same goes for a variable light speed perhaps.
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Post by Cliff »

Dear Davep
As Joe just said, Davep thanks for your input.
I would certainly accept that Mond may be not have been tested. However I am not sure about it being untestable. Having said that I certainly could not test it myself. There is no way that I can make a serious useful contribution to big time cosmology so please do not bother to waste to much time on me except for fun.
Sorry if I am repeating myself but I would love the Big Bang to be correct. But I have to admit that as time goes on the Big Bang theory seems to get more complicated. I think it can be said that the Big Bang theory was initially devised on the basis of observations related to ordinary matter. However, as more observations have been made additional extraordinary things (and not only that but in extremely large amounts - which bugs me) have need to be added to make the theory work.
At the moment I just cannot get my head round that.
However, dare I say it but the idea that light may not travel at the same constant speed everywhere in the universe I can go along with as a possibility (though not as a fact just a possibility). After all if I understand correctly light does not travel at the same speed through all materials.
There was an astronomer who came up with the idea of tired light. I gather it was shown to be wrong but still interesting.
I can even accept the possibility that maybe gravity does peculiar things as well (only a possibility of course). However, I could not possibly prove it.
Best wishes from the grumpy Old Codger Cliff
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Post by joe »

Cliff wrote:if I understand correctly light does not travel at the same speed through all materials.
You do understand correctly Cliff, in a fashion :) . The speed of light, 300,000km/s, is always quoted as the speed of light through a vacuum, a state that exists throughout most of the universe. It still travels at that speed through all other materials also if I understand correctly. The density of a vacuum is obviously negligible and light travels through it without encountering any particles....in theory. A more dense substance like a gas or liquid or even a star will slow the light down because it then hits many more particles. The light doesn't "bounce off" the particle, it is absorbed and re-emitted almost instantaneously but many encounters will have a slowing down effect for the light. The light still travels at 300,000km/s between the particles though.

Light travelling at different speeds in a vacuum elsewhere in the universe seems a bit strange as there is no reason for it to do so. I've not read anything on the subject therefore I'm ill informed.

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Post by Cliff »

Dear Joe
I accept what you are saying. However, I must say that I have always been slightly bugged insomuch as "light travels at whatever specific speed through a true vacuum. However, are there true vaccums anywhere? Possibly between the supposed particles?
If we are not sure quite what Dark Matter is ?, and even more so what Dark Energy is ? Can we be really sure that Dark energy and\or Dark Matter do not affect the speed of light ?.
As I sad I stll favour Big Bang ideas but I am not totally convinced and as things progress I seem to get more unhappy about it, rather than more comfortable. And may be even the old tired light idea may not even be that daft either.
Best wishes from the Grumpy Old Codger Cliff
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Post by joe »

Dear Cliff,

I suppose that Dark Matter and Dark Energy can have some sort of effect on light but that is the light we are seeing. Either DM and DE are present in the universe or they are not, either way the light we see is present in one of those universes. The only way we could tell whether DM and DE had an effect on the speed of light would be to measure it with these things present and then again without them.

I don't suppose there are true vacuums anywhere but one or two protons per cubic metre is pretty close. I think I remember reading that the atmosphere of the Sun is more of a vacuum than anything ever produced on Earth. Scientists.... :roll: Rubbish.

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Post by Cliff »

Dear Joe
Yes, you are right about some of the Sun's atmosphere being thinner than the best vacuum ever produced in a laboratory on Earth.
I read that recently in "The Cambridge Ecyclopeidia of the Sun". I could not remember the exact details so I just checked and it says for example on page 102,.............' The Sun's temperature increases to 10,000 degrees Kelvin in the chromosphere, but the density in the chromosphere drops to roughly a million times less than the photoshere. ........
Whilst page 94 says ..........' The photosphere has an effective temperature of 5780 degrees K but its gases are so rarified that we would call them a vacuum here on Earth.'..................
Sorry to pages in the wrong order but I never do anything the right way round.
I feel almost inclined to say that whichever monthly astronomy magazine produces the most convincing argument that enables me to understand cosmology will get my vote in the forum survey.
Did I hear you say, "absolutely NO CHANCE."
Best wishes from the Grumpy Old Codger Cliff
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Post by Mike Feist »

To Quote 'If we are not sure quite what Dark Matter is ?, and even more so what Dark Energy is ?'

Are they not made-up concepts to fill a flaw in current cosmological thinking!

Mike
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Post by davep »

Mike Feist wrote:Are they not made-up concepts to fill a flaw in current cosmological thinking!
I'd have thought that "made-up" is a little harsh. Probably no more "made-up" than any other hypothesis that seeks to explain various observations.
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