Gravity never zero

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Ivan, Dec 18, 2011.

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  1. Syne Sine qua non Valued Senior Member

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    Is English not your native language? It is just as proper to say: "If you can calibrate some device accurately, then it will make measurements which are precise..." Some knowledge of position does not bar all knowledge of momentum.

    Perhaps this is where you are getting confused.


    As long as you are trying to measure both, you can, only with the accuracy being split between the two properties. If you choose to measure one property exactly, then you cannot simultaneously make a measurement of the other. If you do, the accuracy of your chosen property will suffer.
     
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  3. OnlyMe Valued Senior Member

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    This is getting tiresome...

    The point is you cannot measure both simultaneously...

    You seem to be claiming it is done routinely, and yet fail to present even one example.

    You just keep restating the principle, in various ways. It is a principle and a component of theory. Not an empiricle fact as you claimed earlier.

    Now I am not a quantum physicist, so if you can provide a link to even one example of a simutaneous measurement, I really would be interested.
     
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  5. Syne Sine qua non Valued Senior Member

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    Yes, refusing to understand can be tiresome. Look up electron diffraction and research the reasons for the results of any such experiment.
     
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  7. OnlyMe Valued Senior Member

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    This a dodge. An attempt to change the point of discussion, with more of the same and an attempt to have someone else find your proof. It is not there...

    Remember this?

    Several times you have been asked to provide a specific reference to an experiment that empirically demonstrates simutaneous measurements. Even when some of your own past links state that it is not even theoretically possible.

    I did look and found two cases, not quite fulfilling your claim. One a paper from 2004 that was suggesting an experiment.., a never executed experiment.., and the other a popular article about an experiment that measured position and momentum — sequentially, not simultaneously. (One detcector in front of the other.) and even then much of the uncertainty was in the method of measurement of momentum, which was measured before the exact position not after or at the same time, so its uncertainty doesn't really fit the principle anyway.

    It is time to put up. Provide a link and reference, of any experiment that measured both simultaneously.

    That is after all what the discussion has hinged on. If it is really "very easily" done. It should be very easy to provide a link! So get off the couch and do it.
     
  8. arfa brane call me arf Valued Senior Member

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    Nonetheless, accuracy and precision are not the same thing.

    See this, for instance:

    --http://en.wikipedia.org/wiki/Accuracy_and_precision


    p.s. name one device that gets calibrated "accurately".
     
    Last edited: May 17, 2012
  9. Syne Sine qua non Valued Senior Member

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    Now you are just pedantically contradicting yourself.


    Where you originally said accuracy was about "how well calibrated the measurement apparatus is", you are now saying this is precision rather than accuracy. But this is all just obfuscation. There was no reason to introduce measurement device calibration in the first place, other than to perhaps distract.

    In common parlance, these words are synonyms, and you have no reason to refute that when you've already said "It has nothing to do with the accuracy of measurement".

    Well, I had hoped that eventually you could be enticed to use your own gray matter, but alas.

    http://en.wikipedia.org/wiki/Diffraction#Single-slit_diffraction

    There's even pretty, moving pictures in this one. Compare these, which are easily demonstrated by experiments far too simple to write whole papers on, to this:


    With a bare minimum of scrutiny, you should be able to see how the narrower slit defines a position better, while the wider slit defines the momentum ("the wave looks long and sinusoidal") better. As you vary the width of the slit, the accuracy of each changes smoothly, only barring the measurement of one property when the other is fully resolved.


    Need to be spoon-fed anything else?
     
  10. OnlyMe Valued Senior Member

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    Once again remember this?

    In the double slit experiment (and then only when single particles move through the experiment at a given instant), you can know their position.., which slit they went through, only when they later strike the detector.., some distance after the slit(s), at which time the particles location is no longer at the slit.

    Then over time and repitition of single particles moving through the experiment an interference pattern developes.

    As far as I can tell no one has been challenging the principle. You stated that both position and momentum could be detected SIMUTANEOUSLY. You continue to just point to experiments that demonstrate wave or particle character, or both in a sequential measurement.

    Where is the proof that supports,

    Where you claim it is easy to measure both at the same time............ Instantaneously? It is there where measurement becomes a limiting factor in the empirical evidence. As far as I know we have no measurement device that can measure both simultaneously. Anytime we use two detectors, the measurements are NOT at the same time and it becomes difficult to know what the second measurement would have been, at the time of the first measurement. The act of making the first measurement cannot be excluded as having changed the results of the second.
     
  11. OnlyMe Valued Senior Member

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    3,914
    Once again remember this?

    In the double slit experiment (and then only when single particles move through the experiment at a given instant), you can know their position.., which slit they went through, only when they later strike the detector.., some distance after the slit(s), at which time the particles location is no longer at the slit.

    Then over time and repitition of single particles moving through the experiment an interference pattern developes.

    As far as I can tell no one has been challenging the principle. You stated that both position and momentum could be detected SIMUTANEOUSLY. You continue to just point to experiments that demonstrate wave or particle character, or both in a sequential measurement.

    Where is the proof that supports,

    Where you claim it is easy to measure both at the same time............ Instantaneously? It is there where measurement becomes a limiting factor in the empirical evidence. As far as I know we have no measurement device that can measure both simultaneously. Anytime we use two detectors, the measurements are NOT at the same time and it becomes difficult to know what the second measurement would have been, at the time of the first measurement. The act of making the first measurement cannot be excluded as having changed the results of the second.
     
  12. arfa brane call me arf Valued Senior Member

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    My, aren't we being evasive?
    In common parlance, quantum mechanics is "weird". Somehow, this fails to be a scientific observation. . .

    Just to hammer this home: I said the accuracy of measurement depends on how well calibrated a measuring device is, and that is not a contradiction. The contradiction is in your own mind, I'm afraid.

    Your claim that a device can be calibrated accurately appears to be a misunderstanding (perhaps a common one). Accuracy is how close any measurement is to its "actual" value. Precision is how repeatable a measurement is (read what Wikipedia says again). You calibrate an instrument so you can make repeatable measurements, which are accurate. So calibration is about precision, using a precisely calibrated device means accurate measurements.

    You could calibrate a device accurately, but you would need another precisely calibrated one to do the calibration. Precise = close as practicable to a reference standard (i.e calibrated). Accurate = close to an actual value (determined by measurement).
     
  13. Syne Sine qua non Valued Senior Member

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    Let's count the straw man arguments there.

    1. I never mentioned any double slit experiment. Either you are introducing it to necessitate a delayed measurement or you don't understand a single slit diffraction. In a double slit experiment, it is true that you can only observe either particle or wave behavior, but not both. This is entirely due to what you chose to measure. In a single slit diffraction, the slit can be continuously varied between the width of one wavelength and multiples of one wavelength. At multiples of the wavelength the single slit acts just as if there were multiple sources, with the same double slit interference.

    The difference is that the only measurement is an instant of the detection screen. The interference pattern, whether highly focused or regularly spaced, and everything in between, is an indication of both position and momentum to varying accuracy depending upon the width of the slit.

    2. I am not challenging the uncertainty principle. You conveniently left out the qualifier of "exactly" in order to erect the straw man. Like I've already said, you don't seem to understand the difference between "no simultaneous measurement" and "no simultaneous exact measurement".


    I'll be waiting for a response to what I actually said.

    Evasive? You're the one "hammering" on calibration after you've already said it has nothing to do with accuracy of measurement. You seem to be using this pedantry to dodge the issue entirely.


    And again, is English not your native language? I.e. means that the following is a clarification of the proceeding. "Accuracy of measurement" = "calibration". Now you've added "depends on" all of a sudden. If you realize you made a mistake, just admit it. Don't dishonestly try to rewrite the exchange.

    Just more smoke. What does any of this have to do with the uncertainty principle?
     
  14. OnlyMe Valued Senior Member

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    You are right you did not mention the double slit experiment. You referenced signle slit diffraction. The issue then becomes whether you are evaluating a group of particles or photons or an individual particle or photon.

    From my meager understanding single slit diffraction doesn't involve single photons or quantum particles of any kind. While at least individual photons and electrons can be examined in a double slit experiment.

    While something is learned about light in single slit diffraction, it is difficult to project that to single photons.

    The uncertainty principle involves the measurement of individual quantum particles and/or photons.

    The whole point of simutaneous measurement has nothing to do with how certain either of the two or more measurements are. It has do with it not being possible at quantum scales.

    How many times now have I asked for you to provide even one example of an experiment where two aspects of a quantum particle are measured simultaneously. I don't even care if the results are accurate, just prove it can be done... You claimed that it was easy...

    I am beginning to believe that you are arguing for the sake of arguement.

    Take a little time and read your own references. One of the first even said it was not possible, even in theory... And yet you continue to argue otherwise.

    To be completely clear. Provide a credible reference to any experiment that measures position and momentum of any quantum particle simultaneously. THE MEASUREMENTS DON'T HAVE TO BE EXACT — THEY JUST HAVE TO BE SIMUTANEOUSLY MEASURED.
     
  15. OnlyMe Valued Senior Member

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    Syne, the following quote is the best example of what I have been asking you to provide a reference for. Not the theory but a credible experimental proof.

    For this to be a true statement the measurements cannot be sequential, one and then the other. Continuing to try and divert the discussion by wandering off into descriptions of waves and wave particle duality, is nothing more than an attempt to avoid admitting you were wrong in that quote.

    If you really believe you were right, provide a link to an experiment that demonstrates simutaneous measurements of position and momentum for a quantum particle. (Simutaneous means at the same time.)
     
  16. arfa brane call me arf Valued Senior Member

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    Yes, you are being evasive.

    For instance, I did not say that calibration has nothing to do with accuracy, quite the opposite in fact. What I said was the HUP has nothing to do with the accuracy of measurement.

    Why? Because there is no "actual" value for either the position or the momentum if one is measured to some arbitrary precision (using, recall, a calibrated system). Hence, there is no accuracy involved.

    So that's what precision/accuracy (in the context of measurement) has to do with the uncertainty principle. It helps if you understand what they are and how they're related. Perhaps you could give that a try?
     
  17. Syne Sine qua non Valued Senior Member

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    You don't even seem to have a rudimentary understanding of the double slit experiment. You seem to think that an individual particle will create an interference pattern all by itself. This is not the case. What does happen is that its wave behavior dictates a probability distribution of where the particle will hit a detection screen. But one particle can only ever hit the detection screen in one place. It is only upon an accumulation of particles, displaying wave-like behavior, that we find an interference pattern, and thus the effect of the particle having traversed two slits.

    A single slit diffraction is not much different. In both, each particle can only hit the detection screen in one place, and in both, it is only at the detection screen that we find the results (of either restricting it to a single slit or narrowing the single slit to one wavelength).

    Quantum eraser experiments prove that, even if we have already determined position (which slit information), we can still recover an interference pattern by effectively erasing such information. Delayed choice quantum eraser experiments show that this "erasure" can even occur after the particle has passed the slits. The final detection screen/coincidence counter is the final measurement of all subsequent manipulations.

    You don't seem to have the tools to understand these four experiments, nor more complicated ones that deal with partial which-slit information, with an associated weaker interference pattern, at the same time.


    Single slit diffraction can be done one photon at a time, just like a double slit experiment. And just like with two slits, it takes an accumulation of photon hits to see the underlying probability distribution.

    At this point, I'm starting to assume you may just be a lost cause.

    *Sorry, apparently it wasn't clear that the "it" I was referring to was the uncertainty principle, just like what I quoted you as saying immediately after that:

    You should research partial which-path information in experiment,... or just read what every credible reference on the subject clearly says. Of course, you can also choose to ignore it all, like OnlyMe.
     
  18. OnlyMe Valued Senior Member

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    Obviously you are not reading posts or you are intentionally misrepresenting what is posted.

    The portion in bold above, does connect the interference pattern to more than one event.

    And you still avoid answering my question and/or providing any proof to support the quote below. Show any proof of a simutaneous measurement of both position and momentum for a quantum particle.

    Or how it seems to be in conflict with the bold portion of the following quote from one of your earlier links.

    Uncertainty Principle
    The uncertainty principle also called the Heisenberg Uncertainty Principle, or Indeterminacy Principle, articulated (1927) by the German physicist Werner Heisenberg, that the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory. The very concepts of exact position and exact velocity together, in fact, have no meaning in nature.​


    You seem to be interested in nothing but evasion, misrepresentation and straw man arguments. Likely because you cannot provide any reference of any simutaneous measurement. As stated in the quote above, "the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory." — Let alone in practice.

    One more time prove otherwise.
     
  19. AlexG Like nailing Jello to a tree Valued Senior Member

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    An interference patterm can be produced by a single photon. (or electron, which is what is often used in the double slit).
     
  20. Syne Sine qua non Valued Senior Member

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    Then why don't you find me a single credible reference that doesn't include the qualifier "exactly", or similar. Alternatively, why don't you explain to me why every reference painstakingly says things like "exact position" and "exact velocity". Why not just say "the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory"?

    It is you who keeps conflating "no simultaneous measurement" with "no exact simultaneous measurement" without justifying how you do so, in the face of every reference on the subject.
     
  21. Syne Sine qua non Valued Senior Member

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    Since when?
     
  22. OnlyMe Valued Senior Member

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    That has not been my understanding, at least in the classic set-up. It has been my understanding that when single photons pass through one of two slits they are registered as a discrete particle at the detector. When this is repeated the pattern that developes mirrors the interference pattern seen when a beam of light is sent through the experiment.

    See WiKi Double slit experiment, Interference of Individual Particles.
     
  23. OnlyMe Valued Senior Member

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    I said I don't care if your reference is to an experiment with inexact measurements. All I have been asking is for a reference to an experiment with simutaneous measurements of any accuracy, for quantum particles or photons.

    The UCP is about the uncertainty of knowing two measurements with certainty simultaneously. The empirical fact is that we do not have the ability to measure both at the same time, even in theory.

    Do you get it? Position is measured at an instant.., a point in space, while momentum or energy is always measured over time. While you are measuring momentum position is changing. We have no detectors that can measure both, at the same time, at quantum scales. The closest we can get is to make sequential measurements, which give us no information about simutaneous values.

    Read slowly and more than once if you have to. I know I do not explain things well all of the time. Do you get it now?
     
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