The laws of physics

1 Paul P. Budnik Jr.	The laws of physics	donderdag 6 september 2001 18:39
2 Uncle Al	Re: The laws of physics	vrijdag 7 september 2001 22:41
3 Chris Hillman	Re: The laws of physics	zaterdag 8 september 2001 5:59
4 Lubos Motl	Re: The laws of physics	maandag 10 september 2001 23:01
5 Patrick Reany	Re: The laws of physics	zondag 16 september 2001 18:27
6 Paul Leo Jacoby	Re: The laws of physics	zondag 16 september 2001 18:27
7 Chris Hillman	Re: The laws of physics	maandag 24 september 2001 2:45

"Paul P. Budnik Jr." wrote:

>

I saw a rerun of the Nova TV show on time travel last night that bothered me. It seemed to present mathematics as if it were physics. By playing with the mathematics of general relativity and quantum mechanics it is apparently possible (with some fudging from quantum gravity) to construct worm holes that would permit a limited form of time travel. While such speculation can be fun and interesting I think it needs to be clearly labeled as mathematics whose relevance to physics is pure speculation. The contemporary laws of physics are not a description of how nature works. They are only the most accurate description we have of how nature *appears* to work in a limited experimental domain. What happens outside that domain is unknown. If we start taking our existing models too seriously we become blind to reality. Historically it was very difficult psychologically to get beyond the accepted truths of physical reality given by the great philosophers and religion. We know more today but we are not that different in our tendency to take our contemporary understanding far too seriously.

Kip Thorne had a lot of fun with wormholes. The math is enticing, the physics is unobtainable. We move on.

Physics is applied math, and nobody has yet come up with something better than Newton's calculus for modeling the universe. (We're still waiting, Stephen Wolfram!) All forseeable miracles will be incremental rather than revolutionary unless somebody gives something a real boot to the head. It's been done - Riemann, Bolyai and Lobachevsky called out Euclid, and Einstein capitalized on it. Then people got naughty with Planck's constant.

Note the "applied" part. Theoretical investigations are held in very high esteem indeed, especially if there is no empirical test of their allegations. Experimentalists are viewed as rather dirty beasts often ruining a good party with their muddy hobnailed boots. Science as a whole has degenerated into a centrally administered exercise wherein management has triumphed over accomplishment. Theory is a darling here, being mostly impenetrable and infinitely malleable as the political winds blow. Don't you dare have an original experimental thought! PERT and GANT charts won't accomodate it, nor will granting agencies' spreadsheets. Experimentation leaves physical evidence behind (We have *always* been at war with Eurasia, er, East Asia. Goldstein again!). If you cannot guarantee an outcome you will not be funded. (Bootlegging research is insubordination is heresy is felonious embezzlement of laboratory funding.)

Serendipity is looking for a needle in a haystack and finding the farmer's daughter. Don't throw the babe out with the chaff. Play! When you look around you find stuff. Know what to keep and what to abandon.

http://www.mazepath.com/uncleal/eotvos.htm

It asks a new question, and that is sin enough.

-- Uncle Al
http://www.mazepath.com/uncleal/ http://www.ultra.net.au/~wisby/uncleal/
(Toxic URLs! Unsafe for children and most mammals)
"Quis custodiet ipsos custodes?" The Net!

On Thu, 6 Sep 2001, Paul P. Budnik Jr. wrote:

>	I saw a rerun of the Nova TV show on time travel last night that bothered me. It seemed to present mathematics as if it were physics.

First of all, let me point out that humans owning T.V.s but living outside the U.S., or readers who have some other excuse for having missed the broadcast, can obtain written transcripts of NOVA programs here:

http://www.pbs.org/wgbh/nova/transcripts/

Specifically, I assume Paul is discussing this program:

http://www.pbs.org/wgbh/nova/transcripts/2612time.html

(You can't say much in a 50 minute TV program, so this transcript can be read in a few minutes. I assume it -is- complete, in part because it even includes the commercials.)

After reviewing the transcript, I think it would be fairer to say that that this program talks very sketchily about lots of -mathematical physics-, most of which can fairly be described as "highly speculative". Because NOVA interviewed a dozen leading physicists, who hold -very- different views on the possible reality of "time travel", "traversable wormholes" [had there been time and had this topic retained its brief popularity, they could have discussed "warp drives" too; all three subjects are closely related], I would expect that any intelligent viewer will realize that the show describes an intense ongoing debate at the frontiers of current research.

>

By playing with the mathematics of general relativity and quantum mechanics it is apparently possible (with some fudging from quantum gravity) to construct worm holes that would permit a limited form of time travel. While such speculation can be fun and interesting I think it needs to be clearly labeled as mathematics whose relevance to physics is pure speculation.

As the show makes clear, there is a -very- wide diversity of opinion among leading physicists about how plausible these various different ideas are, and furthermore the opinion of each individual can evolve (c.f. the case of Kip Thorne's evolving views, which are sketched in the show). Again, since several people interviewed flatly contradict the viewpoint of other interviewees, I think the implicit point of the show is that physics is continuously evolving and that each era has its major arguments; this show concerns one of the major arguments of our own time (no pun intended), which at present appears far from any definitive resolution (although history shows that such situations can change very quickly with the introduction of a brilliant new idea or technique).

By the way, for those who want to judge for themselves, here are some relevant papers by some of the people interviewed in the show:

Kip Thorne:

http://xxx.lanl.gov/abs/gr-qc/9308009

Igor Novikov:

http://xxx.lanl.gov/abs/gr-qc/9607063

http://xxx.lanl.gov/abs/gr-qc/0007064

Matt Visser:

http://xxx.lanl.gov/abs/gr-qc/0003025

http://xxx.lanl.gov/abs/hep-th/0004022

Stephen Hawking:

http://xxx.lanl.gov/abs/hep-th/9409195

Raymond Chiao:

http://xxx.lanl.gov/abs/physics/0101068

Guenther Nimtz:

http://xxx.lanl.gov/abs/physics/0104063

Here are some further recent relevant preprints:

http://xxx.lanl.gov/abs/gr-qc/0012089

http://xxx.lanl.gov/abs/gr-qc/0102077

http://xxx.lanl.gov/abs/gr-qc/0003092

http://xxx.lanl.gov/abs/gr-qc/9905033

http://xxx.lanl.gov/abs/gr-qc/9805019

This is just a very small sampling of the relevant literature; even a casual search of the LANL server will turn up many more papers.

>	The contemporary laws of physics are not a description of how nature works. They are only the most accurate description we have of how nature *appears* to work in a limited experimental domain.

I always find it very hard to believe that any working physicist could not accept this as a fundamental verity of physical science. And I am pretty sure that -all- of the people interviewed by NOVA for this show -do- recognize the essential role of experiment and observation. For example, many of Matt Visser's recent papers have dealt with forthcoming attempts to verify experimentally the existence of analogues of Hawking radiation, and most of Kip Thorne's recent papers have dealt with forthcoming attempts to directly verify the existence and predicted properties of astrophysically generated gravitational radiation. Raymond Chiao and Guenther Nimtz are famously arguing about the correct interpretation of Nimtz's experiments. Hafele and Keating are, well, "Hafele and Keating" :-/ Etc., etc.

>	What happens outside that domain is unknown. If we start taking our existing models too seriously we become blind to reality.

I am confident that this is not a danger in the case of time travel/traversable wormholes/warp drives, because most papers on these subjects make it pretty clear that their authors know this stuff is highly speculative. Not surprisingly, for the program in question, NOVA sought out and interviewed a few physicists who happen to hold particularly strong (and mutually inconsistent!) views. My impression is that most authors who have written papers in these areas are not as confident of the correctness of their current viewpoint on various aspects of this stuff as are three or four of the people who were interviewed by NOVA for this particular program.

Chris Hillman

On Fri, 7 Sep 2001, Chris Hillman wrote:

>	First of all, let me point out that humans owning T.V.s but living outside the U.S., or readers who have some other excuse for having missed the broadcast, can obtain written transcripts of NOVA programs here:

I would like to tell you that the most successful TV station in Central and Eastern Europe is called TV NOVA. NOVA entertains you. :-)

http://www.tv-nova.cz/

>	After reviewing the transcript, I think it would be fairer to say that that this program talks very sketchily about lots of -mathematical physics-, most of which can fairly be described as "highly speculative".

Yes, I agree. My feeling is that especially the discussions on time travels usually emphasize whether a solution of Einstein's equations exist but they already don't spend too much time by the question whether it can be actually realized. The existence of a solution certainly does not guarantee that something like it can exist in reality. Namely the existence of closed time-like curves etc. must be considered very carefully. There has been a lot of confusion about various periodic completions of the solution for the black holes. The actual black hole arising from a collaps of the black hole looks much more boring!

A different type of object. Even if a solution for a wormhole exists and seems to be realistic according to the classical equations, such a wormhole can be - and usually is - affected by the possible quantum decay channels (visible as negative modes around this background) that usually make any configuration like that extremely unstable.

>	subjects are closely related], I would expect that any intelligent viewer will realize that the show describes an intense ongoing debate at the frontiers of current research.

Actually I don't think that this topic lies "at the frontiers of current research". Without deeper principles one cannot answer such questions although the gentlemen are certainly very famous and smart. For instance, several string theorists studied the question which singularities in General Relativity are "good" and can occur in reality (after they are smoothed out) and which are the "bad" ones. Today, people know much more about those things but a complete understanding is very far.

Thanks for your references.
Lubos
______________________________________________________________________________
E-mail: lumo@matfyz.cz Web: http://www.matfyz.cz/lumo tel.+1-805/893-5025
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Superstring/M-theory is the language in which God wrote the world.

"Paul P. Budnik Jr." wrote:

>

[snip] The contemporary laws of physics are not a description of how nature works. They are only the most accurate description we have of how nature *appears* to work in a limited experimental domain. What happens outside that domain is unknown. If we start taking our existing models too seriously we become blind to reality.

What's wrong with mere speculation?

Patrick

http://www.ajnpx.com

"Paul P. Budnik Jr." wrote:

>

I saw a rerun of the Nova TV show on time travel last night that bothered me. It seemed to present mathematics as if it were physics. By playing with the mathematics of general relativity and quantum mechanics it is apparently possible (with some fudging from quantum gravity) to construct worm holes that would permit a limited form of time travel. While such speculation can be fun and interesting I think it needs to be clearly labeled as mathematics whose relevance to physics is pure speculation.

[...]

I agree completely. Now tell me how one can see a signal travel faster through a substance and not conclude that light can travel different speeds? Why would any one jump to a conclusion that it travel faster than time? Nobody should think speed of light is fixed in all mediums the same speed. else how could a prism work.

[Moderator's note: The speed of light in some medium is one thing, the speed of light in vacuum quite another. Followups set to sci.physics.relativity, where discussion of such issues belongs. -MM]

-- "Engineers will be quick to tell you why it is impossible ... They have been trained to prove mathematically that it can't be done ...Thank goodness the calculations that "proved" it was impossible for man to fly were wrong!"

THINK CAREFULLY -- IT'S DANGEROUS
EXCELLENCE IS ALWAYS HIDDEN IN THE DETAILS pj
pjacoby@charter.net
http://www.angelfire.com/il3/thruster/

On Mon, 10 Sep 2001, Lubos Motl thanked me for some references and wrote:

>	For instance, several string theorists studied the question which singularities in General Relativity are "good" and can occur in reality (after they are smoothed out) and which are the "bad" ones. Today, people know much more about those things but a complete understanding is very far.

Do tell!

(E-reference? Can I understand it without knowing anything about string theory? If not, can you summarize what people know?)

I missed this intriguing remark last week only because I missed -everything- related to science last week.

Chris Hillman

Home page: http://www.math.washington.edu/~hillman/personal.html

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