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Double slit in time experiment = evidence for quantized spacetime

  1. Aug 28, 2005 #1
  2. jcsd
  3. Aug 28, 2005 #2

    ZapperZ

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    Oh really? How do you justify that claim? And isn't it strange that such a thing isn't even something the paper even mentioned?

    Zz.

    P.S. If you do a search on here, you would have seen that result has already been discussed in at least a couple of threads.
     
  4. Aug 28, 2005 #3
    In the classic double slit an interference pattern is detected because the electron passes through both slits at once relative to the detector – ie: its in two places at the same time, thus the classic experiment is regarded as evidence for the quantisation of matter over space - wave/particle duality etc.

    Classic double slit (Double Slit in Space). Space (x axis) vs Time (y axis)

    + electron source
    t
    |
    | _ __ _ double slit in space
    |
    |______x electron detector


    In this experiment, the interference pattern (plotted as energy of the electron) registered at one of the detectors is due to an electron being ejected at one of two possible times. That is, the electron is in two times at the same place relative to the detector. Therefore the conclusion is surely that this is evidence for the quantisation of matter/energy over time.

    Double Slit in Time. Time (x axis) vs Space (y axis)

    + electron source

    x
    |
    | _ __ _ double slit in time
    |
    |______t electron detector


    Its little wonder, given the newness of this experiment, that the author is reluctant to postulate ‘wild’ conclusions like evidence for the quantisation of spacetime from this experiment, for very obvious fear of just such dismissive responses. It will need to be replicated, scrutinised, etc until people with a career in physics start making such claims.

    Neverthless, as long as the experiment actually does what it says it does – and see posts like Anuj’s

    Interference in time using double slit

    that actually think about the experiment (with no response so far I see) then the conclusion above seems valid.
     
  5. Aug 28, 2005 #4

    ZapperZ

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    Unfortunately, you appear to not understand the QM principle that is reponsible for the interference effects from a double slit experiment. The typical double slit experiment has a lot to do with the measurement of a pair of non-commuting operators. It stands on one of the major postulate of QM regarding the commutation relation of two observables [A,B].

    It means that A and B can be ANY observable, non-commuting operators. The typical 2-slit experiment illustrates the effect of [x,p_x]. The "interference in time" is a reflection of the commutation relation between [t,E]. The reason why this paper is important is NOT due to what you said, but because it hasn't been done before due to the difficulty in the setup.

    Nothing in the PHYSICS of the experiment suggests "quantization of spacetime" (whatever that is).

    If you wish to make your own speculation, may I suggest you reread the PF Guideline that you have agreed to when you signed up. If you wish to continue this, please submit your proposal to the IR sub-forum under Skepticism and Debunking section.

    Zz.
     
  6. Aug 28, 2005 #5
    I appreciate you pbly get a lot of people dizzyingly going on about their TOE or whatever that no-one else has seen, and as a moderator/mentor you try and rein in the junk as much as possible – or at least put it in its own home.

    I agree the experiment shows the reflection of the commutation relation between [t,E].

    However, think about the experimental setup, drawn in plan view.

    The laser is fired perpendicular to the detectors. This produces an electron at one of two times relative to one of the detectors – so the time dimension, relative to the detector, is also perpendicular (x axis). Now the electron travels through space toward the detector – so a space dimension (y axis) can also be drawn.

    So the electron shows a wave-particle duality in time.

    The quantisation of space-time refers to the theory that matter/energy is quantised over the time dimension, as well as the 3 space dimensions.

    I guess it depends on whether you accept the classic double slit experiment as evidence for matter/energy being quantised over the spatial dimensions though.
     
    Last edited: Aug 29, 2005
  7. Aug 29, 2005 #6

    ZapperZ

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    There have been no logical derivation to show such a thing, nor have there been any quantitative example of one. So in both cases, I have not come across any journal papers concluding the same thing you are saying and you have not offered any.

    So my claim that you are making unsupported speculation remains. If you wish to do such a thing, please continue this in the IR section.

    Zz.
     
  8. Aug 29, 2005 #7
    I appreciate the scepticism.

    OK - do you agree that the classic double slit experiment results, performed with electrons, can be treated by the wave/particle duality explanation? That is, the electron, while a particle is also in two places at once – or at least there is a probability it is = interference.

    http://www.upscale.utoronto.ca/GeneralInterest/Harrison/DoubleSlit/DoubleSlit.html#TwoSlitsElectrons

    “If we think that the probability of where the electron is in space is a wave, then when we don't look the probability wave has two pieces at the slits, representing the fact that there is a 50% chance the electron went through the upper slit and a 50% chance it went through the lower slit. These two probability waves from the two slits, then, recombine at the screen and cause the interference pattern.”

    Therefore, with the same reasoning, the double slit in time experiment might also be explained by the electron having a wave/particle duality. Expect, in this formulation, the electron – or the probability of the electron – is a wave in time, not space.

    http://physicsweb.org/articles/news/9/3/1/1/0503013

    shows the diagram of the double slit in time setup.

    See - call the left peak = t1 and the right peak = t2, (the laser fires to the right) so then t2>t1. Now, the page says "interference is observed by the detector on the left because we do not know if the electron was released from the atom by the first or second peak of the laser."

    So the right detector can’t discern what time slit the electron was emitted from = interference = the electron (or the probability of the electron if you like Copenhagen) being in two times at once = wave/particle duality over time = energy quantised over time.
     
  9. Aug 29, 2005 #8

    ZapperZ

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    You are confusing the DETECTION mechanism with the double-slit mechanism. There's a huge difference there. The detection issue occurs whether you have a double slit, a single slit, a gazillion slits, etc. Do a search here in PF regarding the single-slit diffraction. It has more to do with the uncertainty principle than any form of "quantization".

    Secondly, the "wave-particle" duality is only used when describing such phenomena to the general public. Look in a QM text and tell me where there is such a thing in the formalism of QM. There is only ONE, ONE, description of all such phenomena. Marcella has treated and painfully derived the single, double, multiple slit phenomena using purely QM method without having to invoke any kind of "dualism". Again, do a search of PF on "marcella" to see the reference that have been cited many times.

    The "click" or dots, or lines that one detect on the detector has nothing to do with "quantized spacetime". It has everything to do on how we classically detect photons, electrons, neutrons, etc. And in a spectrum, the peak in intensity isn't a quantized space. It is a peak in either the distribution of energy or momentum.

    You have again not able to cite ANY published papers that make the same point you are trying to make. None of the experimental observations make that claim. I believe I've given you plenty of opportunity to do that. If you cannot cite a legitimate source that make the same speculation as yours, please use the IR forum to submit your ideas. This part of PF is not the place to do that.

    Zz.
     
  10. Aug 29, 2005 #9
    Thanks for the reading pointers. So then.

    [E,t]

    The detector makes a measurement of E. Our ability to predict what t will be is undefined. There is a smearing of values on repeated measurement of t. This is the uncertainty principle. (HUP), the ‘wave-like behaviour’.

    The superposition of all the possible emission times causes the interference.

    Is that more like it?

    >>>>

    “the "wave-particle" duality is only used when describing such phenomena to the general public”.

    Well. Physicists only have themselves to blame for confusing the issue.
    However, after reading some of your posts on this, I understand your point - that there is no need for such an artifact in QM.

    Also, many descriptions on the HUP imply that the after measuring A, B is smeared. Possibly, as you claim, they are misinformed. Your point, I think, is that B is fixed, it’s just not possible to *predict* what it will be. It’s a subtle but key point.
     
  11. Aug 29, 2005 #10

    ZapperZ

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    But we don't expect the general public to be delusional enough to walk in from the streets, and without bothering the study the details beyond superficial understanding, to come up with speculations and theories that they want to sell.

    Zz.
     
  12. Aug 29, 2005 #11
    Maybe it should have been 'our ability to predict what the general public will do is undefined once we set up a forum?'

    so I take it you have no violent objection to post #9 then?
     
  13. Aug 29, 2005 #12

    DrChinese

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    It is not true that B has a definite value independent of the observation of A. So I definitely disagree with the implication of your statement. There is plenty of suggest that the "smearing" of B is a literal result of measuring A - see Bell.

    ZapperZ's reference to Marcella describes the double slit interference using terms involving the HUP - so there is no need to resort to wave/particle duality to explain the results. That is because it is the HUP which is at the base of ideas such as Double Slit, Bell, etc. Recall that the basic idea of EPR was that you could "beat" the HUP by measuring A and B on particle pairs. Bell showed that this was incompatible with the predictions of QM (i.e. the HUP). Aspect validated the HUP at the expense of local reality. Marcella shows that the HUP directly fits in to the double slit.

    So any way you cut it, the HUP stands at the base of much of the "weird" phenomena which is QM. To rephrase ZapperZ: look to the QM formalism, and the HUP is a key element of that formalism.
     
  14. Aug 29, 2005 #13
    OK, rewrite. - at the risk of getting off-topic or rehashing HUP posts...

    Many descriptions on the HUP imply that the after measuring A, B is smeared. Possibly, as per Zz, they are misinformed. If I understand Zz (which I may not!) I think he is saying that after A is measured, B is NOT smeared (its fixed?), it’s just not possible to *predict* what it will be. The smearing comes from repeated measurment of B. It’s a subtle but key point.
     
  15. Aug 30, 2005 #14

    DrChinese

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    The implication is that B exists and has a definite value when A is measured. Even if B cannot be predicted, it neither exists nor has a definite value independent of the act of observation. delta A and delta B are restricted by the HUP, and that restriction is fundamental in every sense of the word. It is not just a limitation on the measurement process (or the prediction mechanism), it is a description of the relationship between observer and observed. Experimental results are incompatible with the view that B has a definite value when not observed. So B is not fixed.
     
  16. Aug 30, 2005 #15

    ZapperZ

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    I have written on here, and in my journal, on the misconception of the HUP so many times, I don't think I want to write it anymore. This wasn't my intention when I got into this thread, but rather to seriously question your understanding of QM and what you were reading when you made the speculation regarding the spacetime quantization.

    Zz.
     
  17. Sep 8, 2005 #16
    At the risk of providing more comedy or frustration for Zz et al, I may be able to restate my original point.

    The results from the double slit experiment are explained by the Heisenberg Uncertainty Principle (HUP). The double slit in time experiment provides more evidence for the HUP in that it verifies the relationship predicted by the HUP between E,t (energy, time).

    However, underlying the HUP is the Planck Constant (h), the constant used to describe the sizes of quanta. So, in that the classical double slit provides evidence for the utility of the HUP, it therefore is evidence for the utility of h, one of the five fundamental constants (although h-bar is often used rather than h) that make up Planck units.

    From these (including h) you get the Planck length, which is the ‘quantum of length’, the smallest measurement of length (which defines space) with any classical meaning. We can easily imagine lengths smaller than the Planck length, but such lengths may well have no physical manifestation in our universe. i.e.: talking about their ‘length’ is nonsensical because length is a 'classical' concept that breaks down at that level. That is what I mean when I say the classic double slit seems to follows logically to ‘quantized space’.

    And thus, as the Planck time is the quantum of time, this new experiment follows logically to ‘quantized time’. Taken together = ‘quantized space-time’.

    This thread on PL discusses this.

    https://www.physicsforums.com/showthread.php?t=47592&page=1&pp=15&highlight=planck+length
     
    Last edited: Sep 8, 2005
  18. Sep 8, 2005 #17

    ZapperZ

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    This is illogical. You are saying that just because you "get" h from the double-slit experiment, it proves quantization of spacetime. Now show me HOW you would derive the value of h from this experiment. Go on. I dare you!

    If that is the case, then ALL experiments that can derive the value of h would be experiments that produced the quantization of space and time. Would you claim the photoelectric effect experiment is a quantization of spacetime? Would you argue that the fractional quantum hall effect experiment is also a quantization of space time? So why not pick on those experiments? They are more established, and if you look in CODATA, the STANDARD value of h is obtained from Hall effects measurement. So why not use that experiment? Or is it because you are ignorant of what they are, what they do, and what they signify?

    This is ridiculous!

    Zz.
     
  19. Sep 8, 2005 #18
    no. doesn’t 'prove' the quantization of spacetime. Points *toward* it.

    Well, please do correct my ignorance, but isn’t the whole point of the double slit in time experiment that it validates.

    dE*dt >=h

    ?

    I didn’t say the experiment derives h, I said it supports h. It provides (yet more) evidence for the utility of h. From h you get the Planck length etc et al.

    And yes, any other experiment that supports or derives the value of h could be said to leads to the SPECULATION of quantised space and time via the PL and PT.

    thats all. No TOE claimed here.

    In retrospect I think the thread should have been titled 'double slit in time experiment = more support for HUP' then possibly speculated briefly that this might lead down to more speculation on quantised space-time < which there isn't DIRECT experimental evidence of, or none that I know of.
     
  20. Sep 8, 2005 #19

    ZapperZ

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    No, it doesn't!

    Even the standard double slit is a VERY difficult demonstration of superposition. It isn't transparent for such an interpretation. In fact, even the single-slit isn't a clear demonstration of the HUP - it merely a clear demonstration of the relationship between the knowledge of x and p_x. You do NOT get "h" out of such thing.

    You are threading on very shaky grounds. The paper you cited made no such claim. If you think such thing has any validity, submit it to the IR section. This thread has gone long enough based on speculation.

    Zz.
     
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