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A Are there experimental proofs for modern theories

  1. Feb 26, 2017 #1
    Quantum theory, although hard to understand with intuition has a lot of experimental proof. Do the more modern theories e.g. String theory, or black hole theories have any experimental proof, or are they theories that the mathematics have led to?
    Without proof, do they deserve so much credit.
    Any thoughts much appreciated.
     
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  3. Feb 26, 2017 #2

    phinds

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    String theory has no proof. Black holes are not a theory they are a known phenomenon.
     
  4. Feb 26, 2017 #3

    fresh_42

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    The crucial parts of your question are the words theory and proof.

    A theory in this context is a description that models all known experimental data and preferably allows prognosis about new experiments.
    Therefore, a "proof" is a concept that satisfies these requirements and is free of contradictions. Special relativity isn't proven. It even cannot be proven at all. It is a theory that describes what we know with an incredible precision and had made some testable predictions when it was suggested. This having said, it is natural to look out for theories, which attempt to close the known flaws of our current models. Even more, it is the only way to proceed. To restrict possible models beforehand carries the risk to miss the best one.
     
  5. Feb 26, 2017 #4
    I am not sure why you think special relativity cannot be proven, so far special relativity passed every possible test. Time dilation for example was proven experimentally and it is even used in GPS systems.
     
  6. Feb 26, 2017 #5

    phinds

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    Theories in physics are NEVER "proven", they are just shown to have to best possible correspondence to experimental results but they are still subject to something coming along that doesn't match. Newton's theory of gravity was totally "proven" for quite a long time, so much so that it was called the "Law of Gravity". Only in math is anything ever proven.
     
  7. Feb 26, 2017 #6
    Actually there is no experimental evidence for the existence of black holes. Some physicist even claim that black holes do not exist:
     
  8. Feb 26, 2017 #7

    phinds

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    The trajectories of the stars in the center of the Milky Way have been mapped with enough precision for us to be sure that there is something in the center that is small enough and massive enough that with physics as it is currently understood it can't be anything BUT a black hole. It seems unlikely that there will be new physics that will show that there can be something that small AND that dense that is not a black hole.
     
  9. Feb 26, 2017 #8

    fresh_42

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    I have mentioned this.
    Please don't turn my statement into the opposite by leaving out essential parts.

    But it still isn't a "proof"; it's plenty of evidence though. Newton's gravity is wrong, although it perfectly describes, why I cannot levitate. Would you call it proven then? Proof is simply the wrong word as it suggest a meaning of absolutism, which physical theories do not have, cannot have. The earth isn't flat. However, for the next five miles, it is.
     
  10. Feb 26, 2017 #9
    I agree, my original question asked if there was proof, when I should have asked : Is there experimental evidence that supports the many new theories such as string theory.
    I agree that a consistent theory is a great place to start. But at some stage it surely needs experimental support e.g when observations of the bending of starlight supported Einstein's gravitational theory.

    Thanks for all your comments so far.
     
  11. Feb 26, 2017 #10

    phinds

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    Yes, much better. String Theory hasn't even made any predictions to TEST empirically so there certainly isn't any evidence for it.

    Absolutely
     
  12. Feb 28, 2017 #11
    LIGO proved that black holes exist (and even merge) beyond any doubt. It was not just a discovery of gravitational waves it was also first direct experimental evidence for the existence of black holes as described by General relativity (at least outside the horizon).
     
  13. Feb 28, 2017 #12

    phinds

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    Excellent point. Thanks for bringing that up. I'd forgotten all about it.
     
  14. Mar 1, 2017 #13
    The evidence for string theory is that it is the only non-renormalizable theory gravity. It is the only quantum field theory that predicts the existence of gravity. String theory predicts the existence of gravity, which is not predicted by any other theory of particle physics. Not only that, but it includes all four forces. General relativity includes gravity but nothing else. String theory is internally mathematically consistent, which is quite an achievement. The way anomalies cancel, it makes you feel like it's to much to be a coincidence. It almost eerily predicts black hole entropy. You have string phenomenology, where they can almost reproduce the Standard Model. You have string cosmology. Some people say string theory accurately predicted the Higgs mass. String theory is currently consistent with all observational data. Of course, string theory is still a work in progress. We do not yet have a final theory. However, the universe would really have to be conspiring against us for for string theory to work as well as it does, and not at least be a step in the right direction. You would not have this many physicists continuing to expend this amount of effort perusing string theory if it did not look promising.
     
  15. Mar 2, 2017 #14
    That is just because of a shift in the English language. In past centuries, scientists, regardless of whatever they may personally believe, had to at least publicly pretend that what they were doing were uncovering the natural laws created by the Christian God. Well, we finally got away from that, and quit using the law. In physics, we don't change the names of things, so if there is something that was discovered/invented back when they used the word "law", we still use the old name, but nothing invented within the last century was given the name "law". The individual equations within Maxwell's equations were given the name "law", like "Gauss' law", but Maxwell's equations are collectively called "Maxwell's equations" instead of "Maxwell's laws".
     
  16. Mar 2, 2017 #15

    phinds

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    Yes, string theorists have been saying for about 40 years now that it is wonderfully promising. You'd expect that after 40 years it would be more than a promise ...
     
  17. Mar 2, 2017 #16
    String theory is certainly "more than a promise". It is the most successful theory we currently have of quantum gravity. You are ignoring the tremendous progress string theory has made over the last 40 years devising models which increasingly match reality. What are you comparing it to? Loop quantum gravity? Twistor theory? What attempt to quantize gravity do you think shows more "promise" than string theory? What quantum gravity theory are you claiming is "more than a promise"? If none, then you admit that string theory is the most successful theory we have of quantum gravity. Obviously, there are physicists who are working on other attempts to quantize gravity, but far more physicists work on string theory because so far, it has been more successful. So what do you advocate? Just give up? Not try to reconcile general relativity and quantum mechanics?
     
  18. Mar 2, 2017 #17

    Vanadium 50

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    That's like calling Manos: The Hands of Fate the most successful movie ever made by Harold P. Warren.
     
  19. Mar 2, 2017 #18
    The mere fact that string theory analogs of quantum general relativity formulas are free of ultraviolet divergences is sufficient reason to invest hundreds of years on it.
     
  20. Mar 2, 2017 #19

    phinds

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    Do me a favor. Loan me $1,000. I GUARANTEE you that I will promise you every year into the future to repay you the following year.
     
  21. Mar 7, 2017 #20

    Demystifier

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    A fundamental theory should certainly be free of UV divergences. But effective theory does not need to be so, and it seems that nobody in the string-theory community still believes that strings are fundamental. Instead, the fundamental theory is believed to be something like M-theory (whatever that is) and UV finiteness of string theory seems irrelevant to the finiteness of M-theory.
     
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