Cosmology and Comprehension

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

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joe
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Post by joe »

I think I might have a look at that book by Lisa Ransall. I have just finished a book by a theoretical physicist called Lee Smolin on the subject of quantum gravity. He is speculating that space is discrete at very small scales and that string theory is a kind of larger scale version of something called loop quantum gravity. Wonderful stuff. We might eventually know what space is! And at no cost.
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Cliff
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Post by Cliff »

Dear Joe
I just read the first proper chapter of Lisa Randall's book. I have not read anything frightening yet, and only about 400 pages go. By the way today I got the latest "Scientific American" - it has an interesting article about gravity and holographic two dimensional space.
Best wishes from the Grumpy Old Codger Cliff
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Post by joe »

Cliff wrote:gravity and holographic two dimensional space.
Yes. That's the stuff I have just read about. Of course reading and understanding are two different things :? Bekenstein Bound....this seems important. :? :?
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Post by Cliff »

Dear Joe
Just read Chapter 3 of Lisa Randall's Warped Passages.
I think I am still feeling OK with regards to grasping its contents (but there is always the danger of having missed something crucial). However, having said that I do not think it will be easy (for Lisa or anyone else for that matter to sway me from my stubborn old fashioned "conventional" thinking (whatever that is?). Of course there is a long way to go before I finish reading the book, but already I have read the odd thing that suggests the brane idea might just be another way of looking at things.
Perhaps I should wait until I finish reading the book before making too many comments. I might be a different man then ?
One thing I will say for Lisa Randall (at least from what I have read so far) she does seem to genuinely try to put her ideas into simple terms (at least as far as I have actually read). She deserves credit for that if nothing else.
One thing she did say that mused me. Apparently some of her friends who were not physicists first became impressed with her ideas because at the end of one talk Stephen Hawking invited Lisa to sit with him. Now I know that Hawking is a very renowned scientist. However, from what I have seen of pictures of Lisa Randall (including the one displayed on Warped Passages dust cover) she is a very attractive lady. Irrespective of Hawkings knowledge of physics, I think it could be said he has an eye for the ladies. I could not help thinking Lisa's mention of the matter in her book was made a bit tongue in cheek.
Of course if Lisa was not good looking I suppose I might not have given Warped Passages a second glance.
Best wishes from the Grumpy Old Codger Cliff
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Post by joe »

Cliff wrote: but already I have read the odd thing that suggests the brane idea might just be another way of looking at things.
Dear Cliff,

I believe this sentence might be a lot closer to reality than much of what you have been reading. :wink:
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Post by Cliff »

Dear Joe et al
Can we really take cosmologists seriously?
I used to think cosmologists had reasonable understanding about such things as the Big Bang and supernovae. But increasingly I am begining to wonder ?
Last saturday I attended a talk by a well known cosmologist. He expressed strong doubts about String Theories which he suggests seem likely to be leading nowhere. Amongst other things he said that despite being around since the 1980s String theories in their various forms still have not produced a single tested prediction of any sort. Bare in mind that Relativity had some success despite observing techniques in the early 20th century being much less sophisticated than they are today.
Now it seems that even Supernova explosions are not really all that well understood.
By all accounts a star detonates when the nuclear fuel in its core runs out. The core can no longer withstand gravity and implodes into a super dense neutron star. Most cosmologists seem to go along with that idea.
However, the next step is a puzzle, there currentyly being two main ideas.
a) After the neutron star forms the surrounding stellar matter continues to rains down, then bounces off the surface of the core causing an explosion.
b) The outer layers of the star are blown away by a burst of neutrinos unleashed as the neutron star forms.
By all accounts all attempts to produce computer simulations lead to very disappointing fizzles rather than a bang.
I can only say the above suggests that Supernova explosions are not at all wellunderstood!
However, according to the latest "new Scientist" Adam Burrows and team (University of Arizona, Tusconhave simulated the collapse of an 11 solar mass star and found that oscillations or sound waves were triggered in the turbulent and violently shrinking core. The matter raining down on the neutron star was making it ring like a bell. researcherts suggest this booming effect blasts the outer layers into space. The researchers say the sound waves are "preferentially" radiated in some directions. They say that could explain why neutron stars are often observed being kicked out at high velocity from supernova explosins.
Other researchers say it needs to be seen how these ideas will survive the test of time.
I am inclined to suggest "as one bell ringer said to another - Pull the other one". Bong! bong!
Best wishes from the Grumpy Old Codger Cliff
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Post by davep »

Cliff wrote:Can we really take cosmologists seriously?
Can you give any reasons why we shouldn't?
Cliff wrote:I can only say the above suggests that Supernova explosions are not at all wellunderstood!
Understanding improves with time -- even if it means finding out that your current theories don't work. A step backwards can be a step forwards in understanding.
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Post by joe »

Cliff wrote:Last saturday I attended a talk by a well known cosmologist. He expressed strong doubts about String Theories which he suggests seem likely to be leading nowhere.
He is not alone. Did he suggest an alternative?
Amongst other things he said that despite being around since the 1980s String theories in their various forms still have not produced a single tested prediction of any sort
While this is true I'm not at all sure how easy it is to test for String Theory considering the sizes and the energies involved. Maybe the latest particle accelerators will open a few more doors. Anyway I have read that black holes (a phenomenon of General Relativity) may be the place to look for evidence of the effects of String Theory. Time and space are stretched, or magnified, at the event horizon of a black hole and it might allow us to "see" small things and small times.
The researchers say the sound waves are "preferentially" radiated in some directions. They say that could explain why neutron stars are often observed being kicked out at high velocity from supernova explosins.
According to Sky & Telescope this month the Pulsar B1508+55 in Draco has travelled 60 degrees across the sky in a little over 2 million years. Unfortunately it doesn't say how far away it is - the Cygnus OB Association? Anybody?
I used to think cosmologists had reasonable understanding about such things as the Big Bang and supernovae. But increasingly I am begining to wonder ?
All I can see from what you have very kindly told us Cliff is that cosmologists might have gained a little more knowledge or at least discarded something that was false, which is the same thing.

I have just had my brother stay with me. He is recovering from a ruptured stomach ulcer. For decades doctors have been telling us that these ulcers are formed as a result of diet, stress, lifestyle, etc. etc. but a few years ago some clever people discovered that it is bacteria that causes them. Did we then question the authority of doctors? No we celebrated the discovery and gave the scientist(s) a Nobel prize.

I sometimes feel that because of the perceived frivilousness of cosmology that we are a little to eager to jump on researchers when they have to modify a theory instead of celebrating the advances. It is after all extremely difficult to observe objects at extreme distances and at extremely small sizes let alone even talk about objects that are outside of our narrow human perspective of space and time. Maybe some cosmologists are getting a little ahead of themselves but I'm not at all sure. There are people who predict that String Theory will provide some, if not all, the answers to what the fabric of reality might be but there are almost certainly many more waiting to prove them wrong. That's science.
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Post by davep »

I suspect another thing that tends to really throw people is the popular names that are used for various cosmological hypothesis -- people often seem to take them at face value. Last week, at Newton's AS, we had Prof. Andrew Fabian from the Cambridge IoA giving a talk that was mostly about why Galaxies tend to clump together -- the talk touched on Dark Matter and Dark Energy quite a bit. He made the simple but important point that Dark Matter and Dark Energy are misnomers that, when read without any context, can be misleading. What they seem to refer to is an observed effect that seems to have the property of matter, but which is unknown, and an observed effect that seems to have the property of energy, which is also unknown.

We've seen in this thread, and others, people talking about how Dark Matter and Dark Energy are something that have been "invented" by Cosmologists and, given how odd the ideas seem, they've got to be having us on. As I understand it, far from those terms being evidence of them making something up, they're evidence of an admission that there's still a lot more to be worked out. It strikes me that that's a useful kind of honesty. Prof. Fabian spent some time explaining that, rather than Dark Matter (for example) being a solution to a problem, it was more a case of it being the name of a problem for which a number of solutions were proposed (some more compelling than others).

It seems to me that, when someone reads "Dark Matter" or "Dark Energy" in a text, rather than thinking "here's some crazy made-up idea", it makes more sense to think "here's an admission of a gap in our knowledge, a problem that needs to be worked on and is being worked on".

Interestingly enough a thought came to me during the talk that I'd never really considered before so I had to ask about it at the end of the lecture. When you see "Matter" and "Energy" mentioned you tend to think "equivalence" (although, oddly, I'd not thought about it before in terms of "Dark"). In this case (as I thought would be the case) it's wrong to think in terms of "equivalence" because "Dark Matter" isn't necessarily "matter" and "Dark Energy" isn't necessarily "energy" -- they're just handy names for effects that have been observed.

Disclaimer for the better informed: Any nonsense you read above is not from Prof. Fabian, it's from the corrupting filter that is my brain. Feel free to correct the filtering process -- it will be appreciated.
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Post by davep »

joe wrote:According to Sky & Telescope this month the Pulsar B1508+55 in Draco has travelled 60 degrees across the sky in a little over 2 million years. Unfortunately it doesn't say how far away it is - the Cygnus OB Association? Anybody?
http://hea-www.cfa.harvard.edu/~shami/fastpsr/ wrote:We measure a proper motion and parallax for the pulsar B1508+55, leading to model-independent estimates of its distance (2.37+0.23-0.20 kpc)
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Post by joe »

davep wrote:
http://hea-www.cfa.harvard.edu/~shami/fastpsr/ wrote:We measure a proper motion and parallax for the pulsar B1508+55, leading to model-independent estimates of its distance (2.37+0.23-0.20 kpc)
Good, thanks Dave. I looked up Cygnus OB Association without success. I never thought to look at the object itself :?
What they (Dark Matter and Energy) seem to refer to is an observed effect that seems to have the property of matter, but which is unknown, and an observed effect that seems to have the property of energy, which is also unknown.
Perfectly put.
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Post by Cliff »

Dear Joe and Davep
Yes, i agree that I do seem to be taking an increasingly sceptical line about cosmology. However, i dare not say some of the things I might like to because of the possibility of offending people. I might say too much huffing and puffing, too many theories, for my liking now I think.
Joe. I have not read much more of Lisa Randles "warped Passages" for a few days now. Ironically one section she says the reader can skip passed, I found one of the easiest bits of the book to grasp. However, I am beginning to develope mixed feelings about Lisa's book, but I am still barely 1\3 through it, I However amongst other things i gathe Lisa is not a confirmed "string theorist" she is something of an agnostic about strings I think though strong on many dimensions!
However, just for the moment something that only just struck me.
re: the mention in New scientist about the suggestion that sound waves might have some affect on causing supernova explosions.
I understand that neutron stars are extremely dense. Now i can understand sound waves progating inside the Sun, but i cannot help wondering about the way sound waves propogate in a star as dense as a neutron star?
Incidentally Joe, from what i gather
Best wishes from the grumpy old Codger Cliff
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Post by davep »

Cliff wrote:Yes, i agree that I do seem to be taking an increasingly sceptical line about cosmology.
Good, I don't think blind belief is required.
Cliff wrote:However, i dare not say some of the things I might like to because of the possibility of offending people.
Who do you think might be offended?
Cliff wrote:I might say too much huffing and puffing, too many theories, for my liking now I think.
Theories is what science is about. Everything's a theory.
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Post by Cliff »

Dear Davep
My interpretation of what you say is that you accept that it is right that I should be sceptical about cosmology but as if I was not so in the past. Just to clarify that matter I can say that I have never had blind faith in cosmologists ideas but in recent years what faith I had in them has declined.
Perhaps there are too many cosmologists trying to make a name for themselves. So they feel the need to come up with new ideas, not all of which are ggod ones (indeed too many perhaps).
Another point I would like to try to clear up is that my mention of pusars or whatever travelling at great speed was not to question the validity of the observations that have shown that, I was already aware of that. No I was questioning the validity of the apparently new theory that seemed to be explaining how stars (or at least some of them) get thrown of at great speed by supernova explosions. I might be being naive but I think the idea that supernova expolsions are triggered (or poosibly partly triggered?) by sound waves in neutron stars is not just somewhat but indeed very premature. I have been reading a bit about the Sun recently, and in particular about sound waves travelling about and possibly being reflected by the various layers within the Sun. However, from what I gather those matters are far from well undertstood. That being the case I think it is rather premature to say the least for someone to suggest that sound waves related to neutron stars may be a factor in supernova explosions. I am curious about the nature of sound waves related to stars as dense as neutron stars!
With regards to your comment that everything is theory, well I am not sure quite what that means. I will say though that with regards to theories in general, it is often said that you can never prove a theory is right, you can only prove it to be wrong. However, I think it can be said some theories can be tested at least to some degree. If the test works satisfactorily it is a good theory. If a theory fails a critical test then arguably it is a bad theory. However, even worse in my opinion are theories that can never be tested (or at least not in an acceptable period of time. Of course someone will say well what is a an acceptable period of time? I think each individual one of us as a right to have an opinion as to what that might be.
Best wishes from the Grumpy Old Codger Cliff
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Post by davep »

Cliff wrote:My interpretation of what you say is that you accept that it is right that I should be sceptical about cosmology but as if I was not so in the past.
No, that isn't what I was saying.
Cliff wrote:Perhaps there are too many cosmologists trying to make a name for themselves. So they feel the need to come up with new ideas, not all of which are ggod ones (indeed too many perhaps).
You say that as if it's a bad thing. Do you think it's a bad thing -- coming up with lots of ideas and seeing which will work and which won't?
Cliff wrote:I might be being naive but I think the idea that supernova expolsions are triggered (or poosibly partly triggered?) by sound waves in neutron stars is not just somewhat but indeed very premature. I have been reading a bit about the Sun recently, and in particular about sound waves travelling about and possibly being reflected by the various layers within the Sun. However, from what I gather those matters are far from well undertstood. That being the case I think it is rather premature to say the least for someone to suggest that sound waves related to neutron stars may be a factor in supernova explosions.
I'm not sure I can see how it is "premature". If you observe a mechanism but don't fully understand how it works why would it be premature to suggest that the same mechanism, in a related body, is a variable that needs to be considered?
Cliff wrote:I am curious about the nature of sound waves related to stars as dense as neutron stars!
What's your thinking in this regard?
Cliff wrote:With regards to your comment that everything is theory, well I am not sure quite what that means.
It means what it says. Science, especially (but not just) Cosmology is all about advancing a hypothesis towards being a theory. To complain that there are too many theories is to complain about the very existence of the scientific method.
Cliff wrote:I will say though that with regards to theories in general, it is often said that you can never prove a theory is right, you can only prove it to be wrong.
Correct -- that's an important aspect of the scientific method.
Cliff wrote:However, I think it can be said some theories can be tested at least to some degree.
All theories should be testable -- if they can't be tested then they're not really a theory are they? A theory should be falsifiable; if it is falsifiable then it can be tested; if it can't be tested then it's not falsifiable and it can't really be a theory.
Cliff wrote:However, even worse in my opinion are theories that can never be tested (or at least not in an acceptable period of time. Of course someone will say well what is a an acceptable period of time?
Can you think of a theory that can't be tested? Surely, if you've got an idea that can't be tested, what you've really got is a hypothesis that can't ever become a theory?
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