Mathematical way of testing this statement?

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  • #26
jeff
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Originally posted by marcus
this post communicates a real person to me and if you start QFT threads as you say you might do later then I would (judging by this post alone) be enthusiastic about reading and maybe putting some questions in to the mix in a non-critical way. this is a remarkably nice open-sounding post.

Regards,
Marcus
Sounds great. I'm happy I found a way to strike a positive chord with you. I'll be sure not to forget how while I'm away.

As ever
Jeff.

P.S. It's true that I avoid introducing mathematical notation in my posts. I actually regard papers overflowing with mathematical formalism accompanied by little exposition with suspiscion that the author's are hiding either the fact that their result is trivial or that their understanding of the material is spotty.

In any case, there's in general little need for alot of symbology here. But if at any time for any reason you'd like to see a more mathematical treatment of a question, just let me know. In fact, you remember those unicode symbols I found. I made macros for all of them and am looking for a good excuse to use them. Unfortunately their use is rarely justified here and I don't think having that kind of fun at the expense of someone else's understanding makes sense (though I'm not sure about that).
 
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  • #27
thermonuclear
May I ask respectfully, why of this endless discussion about string theory on curved backgrounds? The question (the requirement put mainly by relativists to a quantum-gravity theory) is not flat or curved background, but background independence. Background dependence means to make use of any predefined solution (usually symmetric solution) of the Einstein Equations and to perturbate it, as done in the usual QFT. Of course string theory supports curved backgrounds in the same way as the usual QFT does (see e.g. the derivation of the Hawking radiation for a beatiful application). The question is whether it supports background independence as LQG does, I belive not. The more interesting question might be whether background independence is actually a necessary requirement. I (and may be also others) get more and more the impression that, although all your discussions could be highly interesting, they lead systematically to focus on the wrong issues, mainly due to personal attacks...what a pitty.

Regards.
 
  • #28
marcus
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Great clarification, thermonuclear, thank you!

Originally posted by thermonuclear
May I ask respectfully, why of this endless discussion about string theory on curved backgrounds? The question (the requirement put mainly by relativists to a quantum-gravity theory) is not flat or curved background, but background independence. Background dependence means to make use of any predefined solution (usually symmetric solution) of the Einstein Equations and to perturbate it, as done in the usual QFT. Of course string theory supports curved backgrounds in the same way as the usual QFT does (see e.g. the derivation of the Hawking radiation for a beatiful application). The question is whether it supports background independence as LQG does, I belive not. The more interesting question might be whether background independence is actually a necessary requirement. I (and may be also others) get more and more the impression that, although all your discussions could be highly interesting, they lead systematically to focus on the wrong issues, mainly due to personal attacks...what a pity.

Regards.
Actually I have started LQG threads to help me learn more about it and have valued other people's input focused on LQG (which does not distract but helps very much)

I am not looking for debate and regret the distraction it represents.

Various people at PF have helped me learn some LQG by working along with me in threads or making suggestions----Rutwig has stepped in, Chroot has helped, Hurkyl has pulled me out of the ditch several times, various people. You, wolram, somebody named Instanton early on gave a thumbnail sketch of LQG that was very helpful. Sauron obviously knows a lot about LQG.

It is hard enough to plow thru some of these papers without having distractions!

On the other hand if others want to start collective-learning threads about QFT or the Standard Model or M-theory or whatever that is great!

It sounds like Jeff might start a QFT thread further down the road.
I would very much respect and appreciate such an effort---tho could not promise participation---and it is clear that there are a halfdozen or so people here currently studying QFT, eg. Damgo, Tom, or knowledgeable about it, like you probably and Sauron. It could be an outstanding thread. Rutwig, you may have noticed, is savvy beyond any doubt.

I'll try to think about what you said, the substantive thing.
The value of backgr. indep seems obvious to me at the moment
as leading to the discrete spectr. of area and vol operators, and
removing the bigbang singularity, and getting some good black hole numbers and just generally triggering a bunch of progress on several fronts. Also it is an incredible challenge to construct a theory with backgr. indep---this also intrigues me: the fundamental newness and difficulty. But the fact that its value
"seems obvious" to me is also a sign that I should re-examine,
as you suggest. Never should take anything on faith.

Best regards
 
  • #29
jeff
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Originally posted by thermonuclear
The question is whether it [string theory] supports background independence as LQG does, I belive not.
I don't think anyone's arguing that string theory is background independent. The question is whether M-theory will turn out to be background independent. There are clues in string theory that M-theory will be a more intrinsically quantum theoretic framework than strings so that the answer could very well be yes, but nobody knows.

Originally posted by thermonuclear The more interesting question might be whether background independence is actually a necessary requirement.
No argument there, and I'm semi-blown away that you made that point because it seems that most peope here consider background independence a given, but in terms of pure logical possibilty - as opposed to plausibility - it's really not.

Originally posted by thermonuclear I (and may be also others) get more and more the impression that, although all your discussions could be highly interesting, they lead systematically to focus on the wrong issues, mainly due to personal attacks...what a pitty.[/B]
You're right and I feel bad about that. Part of the difficulty for me is that I've already learned QFT, string theory, LQG, GR and just about everything else along with all the math so that the problem of how to contribute to the threads dedicated to a combined effort to learn about something without dampening the spirit of the thread has been a bit trickey. Unfortunately those are the threads that interest me most, but as a teacher not a student.

But what am I supposed to do? I don't think it makes sense for me to pretend that anyone here has anything to teach me (though they might). The only alternative is just to stay out of those threads. So either I start my own threads which was not something I initially had any interest in doing, or just leave. The truth is I'm not here to make a contribution. I'm here because I can keep my mind engaged in the kind of low level discussions of physics that help me stay creative in my own research while avoiding having to deal for the same self-serving reasons with students in person who end up taking too much of my time.
 
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  • #30
wolram
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with reverance to MARCUS and JEFF i find it difficult to define something if you dont know ALL of its properties, there seems to be
several ongoing arguments as to what gravity is and its properties
and or how it is conveyed
http://space.com/scienceastronamy/gravity-speed-030116html [Broken]
http://www.ldolphin.org/vanFlandern/gravityspeed.html
http://goodfelloweb.com/nature/cgbi/#b
the last link may be "iffy" but its worth a look
MARCUS ,JEFF are there still as many S theorists working on same as of a few years ago?
how about a poll to see who believes what the best theory is?
top link should be-------------gravity-speed-030116html its ok on original but wont post.
 
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  • #31
marcus
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Just occurred to me I should probably edit out my earlier post
because it was lacking in reserve and dignity. In fact I was
yakking like a moron. However I did enjoy this link, which I think
I got from you, to an item in "physics news update", about gravity.

http://www.aip.org/enews/physnews/1999/split/pnu454-1.htm [Broken]

I've been going over past physics news update (pnu) things today
and like that website very much. The science writers they have there, doing the short summary reports, are serious and dont waste words just being "journalistic". I see you have pointed to several pnu newsitems. Thanks for the lead.

Marcus
 
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  • #32
wolram
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What is the simplest evidence that there are more than 4 dimensions?
There is none. All of the 'evidence' is of the theoretical kind, but none of it has been put to the test because...we don't know how! All we know is that our space-time is 4 dimensional to about a few parts per hundred billion based on how well gravity follows 4-D general relativity inside our solar system.

i found this quote by a respected scientist
--------------------------------------------------------------------------------




------------------------------------------------------------------------
 
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  • #33
marcus
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Originally posted by wolram
What is the simplest evidence that there are more than 4 dimensions?
There is none. All of the 'evidence' is of the theoretical kind, but none of it has been put to the test because...we don't know how! All we know is that our space-time is 4 dimensional to about a few parts per hundred billion based on how well gravity follows 4-D general relativity inside our solar system.

i found this quote by a respected scientist
That is an interesting quote. I'm curious to know who said it, as I would look them up on the web and see what other things they said. Sometimes I am amazed at how much the internet makes science better---that is, more fun and accessible to a wider audience. (Because one of the most fundamental things science ought to be is fun and accessible to a wider audience, if it is that, then it is better science.) If I hear of a person or an idea then it is highly probable that I can find out more about that idea within 3 minutes, and so on.

You have turned up some interesting stuff on the web, you know what I mean. Its great. And every serious "science watcher" has, I believe, a perfect right to express their opinion. You dont have to play football in order to know the teams and who's winning, just like you dont have to be a horse in order to know the odds.
In fact it probably helps if you are NOT a horse. Outsiders make good watchers. I am talking too much as usual. Well, my wife just came in and told me what I have to do for the next hour or so.
Be back later,

m
 
  • #34
wolram
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quote is by Dr Sten Odenwald, im sorry i dont have a link, i downloaded this in the late nineties, i know i should keep urls
 
  • #36
marcus
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Originally posted by wolram
this is the horses mouth
http://cgpg.gravity.psu.edu/research/index.shtml
click on links
i hope you find this interesting
this is a great link. thanks!


I had been to the site before to look up the schedule of talks at
a conference but had never tried "links"

they have books and papers there that I dont know of
being available elsewhere online

the site will keep me busy for a while, am reading
Ashtekar's paper ("Quantum mechanics of geometry" 1998)
now, which I dont remember seeing even a reference to
anywhere else.
 
  • #37
jeff
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Thiemann in this very recent paper includes a useful assessment of the LQG program which I think is worth a look:

http://xxx.lanl.gov/abs/gr-qc/0305080

Perhaps I'll post a summary.
 
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  • #38
wolram
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do you understand all of that JEFF, in my unqualified opinion that is a mathmatical soup deep enough to drown most people
as i understand we should be getting results from satalite surveys soon until then im going to keep from drowning
in the mean time if you have information that a non post grad could understand i would love to see it
 
  • #39
jeff
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Originally posted by wolram
do you understand all of that JEFF
Yep.
 
  • #40
wolram
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analy retentative or what? yep is what my dog exclaimes when i accidently tread on his tail, that sort of reply gets you no points
if you know somthing its not big or clever to keep it to yourself
i thought you were going to be helpful shows how stupid i am, good luck on your ego trip and watch out for icebergs
 
  • #41
jeff
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Originally posted by wolram
analy retentative or what? yep is what my dog exclaimes when i accidently tread on his tail, that sort of reply gets you no points
if you know somthing its not big or clever to keep it to yourself
i thought you were going to be helpful shows how stupid i am, good luck on your ego trip and watch out for icebergs
Some people like starting threads to teach or to create a place where people can learn on a cooperative basis and that's fine. I prefer answering specific physics questions and you haven't asked one. But you're definitely the first to misinterpret one of my "yeps" as "fu*k you". Where did that come from? I didn't deserve that and your way out of line. In fact your post violates rule 5 of the site posting guidelines as spelled out by Janus as follows:

Keep arguments confined to the Ideas and subject at hand, and not on personalities. I also frown on “baiting”; trying to prod the other guy into starting an argument or to delve into personalities.

You know, I have this sort of problem with marcus all the time. The interesting thing is how carefully he's avoided asking me specific physics questions or answering any of mine with anything but personal insults. You owe me an apology and if you can't see that then your the jerk, not me.
 
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  • #42
wolram
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ok jeff i see your point i did step out of line i do apologise,
but you must see it from my side as well, i have been trying to
learn what gravity is now for over a year spending hours on the net
reading books etc, only to find out that the theories are full of holes.
it may ruffle your feathers if i say string theory isnt in "vogue"
it may do the same to other people if i say QLT is in "tatters"
its an uqualified opinion but its the truth as i see it.
im willing to listen and learn from anyone, but i dont want to wast my time in the process..
 
  • #43
jeff
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Originally posted by wolram
ok jeff i see your point i did step out of line i do apologise
I appreciate your apology very much, thankyou. I think we can forget about it.:smile:


Originally posted by wolram
it may ruffle your feathers if i say string theory isnt in "vogue"
People here are much more interested in LQG than strings, which is fine. The most important thing to me - and I've posted this a number of times - is that LQG provides an interesting opportunity to learn some neat physics and that's exactly what's happening. In any event, even if LQG is wrong - as most high energy theorists believe - there's evidence that it's telling us something about QG that we don't yet understand.

If it was my intention to shove strings down everyone's throats here I would've started my own threads on the subject. So unless someone explicitly says something about strings, I tend not to mention it. Besides, unlike LQG, strings can't be understood by reading two or three judiciously chosen papers. Strings also require a solid foundation in QFT, and alot more math, neither of which people here have. Anyway, the scope and nature of LQG and strings are very different and nobody really needs to choose between them.

The most important omission in the threads about LQG are discussions about it's central unresolved issue of how to solve the hamiltonian constraint and finally determine it's quantum dynamics and whether it has GR as it's classical limit. Like I said, maybe I'll try to throw something together to explain this.
 
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