# Science approaching science fiction

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1. Mar 9, 2010

### Blenton

I hate it how science is fast approaching the realms of science fiction, it seems as if it diminishes the quality of the real subject. Trying to explain principles of general relativity and quantum to my father, and it sounds like some script from startrek. How can it be taken seriously by any layperson when theyre just as crazy?

2. Mar 9, 2010

### Pinu7

Fact: Nature is weird.

3. Mar 9, 2010

### Ivan Seeking

Staff Emeritus
Note that the best science fiction is merely an extrapolation, albeit far-fetched in most cases, of known science.

The fact is that you are complaining about theories that are already a century old, or nearly so! Relativity and QM predate Star Trek by 40-60 years. Just tell dad that this stuff has been around longer than he has. In terms that we, in this fast-pace world of rapidly evolving technolgy, are familiar, the Relativity and QM theories are ancient; and most importantly, well tested.

Last edited: Mar 9, 2010
4. Mar 9, 2010

### KrisOhn

Heh, if you find QM and Relativity weird, you should check out some string theory. String theory is something that I find pretty outlandish at times.

5. Mar 9, 2010

### humanino

I have strong doubts. Let me remove supersymmetry as a prediction belonging to string theory itself. Supersymmetry is quite a prediction, it can be interpreted in superspace as the addition of fermionic dimensions to our beloved familiar up/down-left/right-front/back bosonic dimensions, but it does not require string theory, or if it does, one has to argue about local supersymmetry as a gauge, that is to say supergravity and M-theory, which I will assume would take us too far. What I mean to say is, quantum mechanics in itself is quite weird already and this is often overlooked. For instance, it is pretty well established that local determinism is dead by the violation of Bell's inequalities, although some people on this very forum seem to have time to discuss it. To me, for instance additional (bosonic) space dimensions, be them curled up, are rather pale and straightforward extension in comparison with the death of local determinism. Can you give an instance of string weirdness which, according to you, supersedes quantum mechanics ?

Although I could quote amazing predictions such as antimatter by Dirac, or the pion by Yukawa, the simplest prediction from quantum mechanics + relativity which is often overlooked and I wish to emphasize is the following : all electrons are the same. Offering a solution to this puzzle is astounding. We tend to take for granted previously established answers to simplest questions which once upon a time seemed simply impossible to address.

6. Mar 9, 2010

### Galteeth

I was reading a bit about the fusion experiments that will be going on at the national fusion center in scientific american. That laser they are using to initiate the fusion sounds an awful lot like the "phaser" from star trek!

7. Mar 9, 2010

### Ivan Seeking

Staff Emeritus
Check out the size of the memory devices that Spock uses in the original series. They are arguably out of date! It struck me one day that much of TOS is no longer sci-fi. No warp drive or human transporters, but many of the practical devices used are now mundane.

The modern cell phone pretty handily competes with Kirk's communicator.

8. Mar 9, 2010

### fluidistic

I don't want to be off topic in any way, I just want to say thank you for this little comment
. I gave up trying to explain that indeterminism is present in QM and in any other theory that pretends to replace it (as proven it seems by physicists, but I don't remember where I've read this). People saying that determinism still exist and that QM has some "God" idea in it were not physicists. I'm just glad to know that a physicist agree on the fact that "local determinism is dead".

9. Mar 9, 2010

### Ivan Seeking

Staff Emeritus
Huh, I assume, Humanino, that by "some people", you are referring to non-physicists?

10. Mar 9, 2010

### KrisOhn

While I remotely grasp what you are talking about in your initial paragraph, note that I am only a first year mathematical physics student and I will not be able to parallel your level of understanding.

I also now understand what you mean when you say that quantum mechanics is plenty weird enough without being given due credit. I am thinking now I should have held my tongue, as there is much I do not know.

But, on with it.
It is not necessarily string theory itself that I find particularly weird, as you said, it is easy to visualize extra dimensions being wrapped up. What I find weird is but a spawn off of some of the math used in string theory; called Dirichlet branes.

I quote from String theory lecture notes by Gerard't Hooft. Found here: https://www.physicsforums.com/showthread.php?t=383289 Page 41.

This whole notion of branes, is quite bizarre to me, perhaps it is because I cannot visualize it, or maybe its because I cannot understand the notion of having more than 3 internal dimensions while there are only 3 external dimensions. It is a very interesting subject though.

Last edited: Mar 9, 2010
11. Mar 9, 2010

### humanino

Thanks for offering an answer. The full weirdness of D-brane I think can only occur in M-theory, which I already acknowledge could supersede quantum mechanics, and as we do not know yet I did not want to go into. But in principle I could agree, although brane model building remains usually quite traditional geometry, not weird at all in comparison with non-commutative geometry which is _the_ geometry of quantum mechanics.

Otherwise, probably my most useful comment here, the exponent can be obtained with brackets x^{25} :
$$x^{25}$$
(in general, you can click on the code to see the LaTeX source)
There are physicists who insist to keep quantum mechanics deterministic, or at least investigate whether it could be the case in principle, some of whom have achieved in a few weeks more than I will achieve in my entire life
Determinism beneath Quantum Mechanics

Last edited: Mar 9, 2010
12. Mar 9, 2010

### KrisOhn

Not sure if that is sarcasm, tough to catch on forums. But the three dots were meant to annotate sections that I did not need to quote.

And thanks for the info; both of physics and code.

13. Mar 9, 2010

### humanino

No, that was not
I used three dots myself as a reference to the message I was answering, your entire message, without needing a specific quote from it.

P.S.
I also have communication issues when facing people in real life. Seriously.

14. Mar 9, 2010

### Leptos

Join the club. Have you see the relationship section on PF?

What do you guys think of Edward Witten, Leonard Susskind, David Gross, Yoichiro Nambu, Michio Kaku, and so on?
They seem like brilliant people, but wouldn't it be better if guys like them weren't string theorists?

15. Mar 9, 2010

### humanino

I only send private messages to Cyrus, he's a great advisor for relationship issues.

16. Mar 9, 2010

### ZapperZ

Staff Emeritus
Your starting premise is faulty. Try explaining flight or a TV to a primitive tribe. They'll think YOU are crazy.

What YOU consider to be crazy, many of us accept easily and USE every day.

Zz.

17. Mar 9, 2010

### humanino

BTW KrisOhn, I am sorry if I offended you with my answer, as a first year student I trust you will soon understand this business better than me.

18. Mar 9, 2010

### KrisOhn

Hah, I am with you on that one. I find I talk faster than I think, and that can turn into a problem sometimes. But I am working on it.

Oh! Not at all! It was I that should have held my tongue, but I am kind of glad I didn't. I find that discussions/arguments are the best way to realize what you know, and more importantly, what you don't know. All in all, I'm glad people challenge each other, I don't think science would be as far along as it is today without that.
Thanks

19. Mar 11, 2010

### Ivan Seeking

Staff Emeritus
20. Mar 11, 2010

Bingo!

Blenton, try to see this as an opportunity to catch up instead of watching the train pull away. If your trouble is in explaining it to a layperson, consider it an opportunity to gain a greater/new conceptual understanding of a given topic. It is very exciting, and rewarding, to find new ways to explain things.

21. Mar 11, 2010

Quoted for truth!!

One of the great things about PF, for me personally, is that is shows me on a daily basis just how much I don't know. With an endless amount of knowledge to obtain, it is inspiring to be constantly humbled by the fountain of wisdom that is PF and the people who make up its community.

22. Mar 11, 2010

### EnumaElish

I never quite understood this proposition. Surely, two electrons are differentiated by their positions in space?

Also, I read that electrons in a vacuum (in the form of cathode rays) travel at speeds below the speed of light; is that measurement consistent with theory?

23. Mar 12, 2010

### ZapperZ

Staff Emeritus
[Edit: After reading humanino's response, I may have misinterpreted your question, so the discussion below may not be relevant.]

Let me give you 2 identical ping pong balls... oh wait, can we say that? Of course we can! What this means is that you have 2 entities that have identical characteristics in all aspects. They obviously cannot be at the identical location in space, but that has never been a criteria of classifying something has being the same. If it is, then the phrase "2 identical objects" of any kind can never been used or be correct.

So being separated in space does not make 2 things not identical. But having said that, for electrons, if they are close enough to each other that their wavefunctions have a significant overlap, then their "indistinguishibility" kicks in even more via a quantum statistics called the Fermi-Dirac statistics. In this case, they are even more "alike" in the sense that you can no longer track each of them separately, even if they are separated in space.

Not sure what is not inconsistent here. Since an electron has a mass, at best, they can only get just below c, albeit, at 0.99999c. For most practical purposes (i.e. in doing calculations), any time the electrons energy is above 1 MeV or so, we approximate the speed to be practically c.

Zz.

Last edited: Mar 12, 2010
24. Mar 12, 2010

### humanino

I will try to argue in the spirit of Feynman's "The reason for antiparticles"
It is formally possible to describe an antiparticle moving forward in time as its particle moving backward in time. If one chooses to do so, it is always possible in a finite system with two electrons to describe one electron exiting the system in the far future, annihilate with its antiparticle (for instance like in the diagram below)
One can construct the antiparticle as one wishes, since the annihilation takes place in the far future of the finite system. So one can claim that the antiparticle came from the distant past of the finite system. One can in the far past reverse the above diagram so that one obtains a pair creation. Thus we obtain an electron in the distant past which we can take to be emitted in the general direction of our finite system and eventually become the second electron of our system !

This can be re-interpreted as saying that the two electrons in our finite system are really one and the same electron line.

This little tale is one way to interpret the necessity that, in quantum field theory, there is only one electron field, all electrons in the Universe being excitations of this single field, and we can always arrange the electrons' configuration in a single system so as to have just one external electron line.

Please note that there is no claim that all electrons in the Universe are just the same line going back and forth in a particle and antiparticle cosmic billiard game. The claim is that quantum field theory must be able to deal with the situation if it were happening. We can never prove with a finite system that this is not what is happening. If two electrons were distinguishable, we could prove this scenario wrong.

edit
I realize that it might appear odd why this little tale is relevant to justify the depth of quantum field theory. After all, it's just a simple tale, why did people need quantum field theory to come up with it ? Because near the beginning, it claims "antiparticles moving forward in time can formally be described as particles moving backward in time". Strictly speaking, one must also reverse their handedness. This claim is an essential ingredient of the tale, and it made sense only with quantum field theory.

Last edited by a moderator: Apr 24, 2017
25. Mar 12, 2010

### Andre

Humanino, it looks that svg (scalable vector graphics) is not very common and it appears that it will not display. Could you convert it to jpg perhaps?

Last edited by a moderator: May 4, 2017