Gravity-Detecting LIGO Also Found To Be Creating Gravity Waves (sciencemag.org) 82
LIGO is a large-scale physics experiment to detect "ripples in spacetime," as well as gravity waves from outer space. But it turns out that it's also creating gravity waves, according to a team of physicists led by Belinda Pang, a physicist at the California Institute of Technology. sciencehabit quotes Science magazine:
Although these waves are far too feeble to detect directly, the researchers say, the radiation in principle could be used to try to detect weird quantum mechanical effects among large objects... Of course, LIGO doesn't generate large gravitational waves -- you could probably make bigger ones yourself by whirling bowling balls around -- but it does so with optimal efficiency [and] the waves could still be used to probe quantum effects among macroscopic objects, Pang says.
Quantum mechanics says that a vanishingly small object such as an electron can literally be in two places in once. Many physicists suspect that it might just be possible to coax a macroscopic object, such as one of LIGO's mirrors, into a similar state of quantum motion. That delicate state wouldn't last long, as interactions with the outside world would make it "decohere" and put it in one place or another. However, one could imagine measuring the rate at which such a state decoheres to see whether it matches the rate expected from the radiation of gravitational waves, Pang says.
"It's unbelievably difficult," Pang says. "But if you want to do it, what we're saying is that LIGO is the best place to do it."
Quantum mechanics says that a vanishingly small object such as an electron can literally be in two places in once. Many physicists suspect that it might just be possible to coax a macroscopic object, such as one of LIGO's mirrors, into a similar state of quantum motion. That delicate state wouldn't last long, as interactions with the outside world would make it "decohere" and put it in one place or another. However, one could imagine measuring the rate at which such a state decoheres to see whether it matches the rate expected from the radiation of gravitational waves, Pang says.
"It's unbelievably difficult," Pang says. "But if you want to do it, what we're saying is that LIGO is the best place to do it."
"...these waves are far too feeble..." (Score:2)
Figures (Score:2)
Gravity wave != Gravitational wave (Score:3, Informative)
Re:Gravity wave != Gravitational wave (Score:5, Informative)
https://en.wikipedia.org/wiki/... [wikipedia.org] -- waves on the surface of water whose dynamics is dominated by gravity. See https://en.wikipedia.org/wiki/... [wikipedia.org] for smaller ripples dominated by surface tension.
https://en.wikipedia.org/wiki/... [wikipedia.org] -- what the fucking article is about
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There's a VERY important difference, however. I think it's more about getting this shit fucking correct. Even TFA spells it out properly...not sure how that was missed in TFS. Oh, Slashdot, you keep me young.
Copenhagen Interpretation (Score:5, Informative)
No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.
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*Technically, the square modulus of the wave function.
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Sorry for the physics rant; I feel better now.
Re:Superposition (Score:1)
Re:Copenhagen Interpretation (Score:5, Informative)
(Sorry for the delay in answering; Sunday night movie with the wife. :-) )
The term "superposition" means, in this context, two things--or rather, one thing, but expressed two ways:
(1) Given a particular physical setup--the collections of forces (or, equivalently, sources of potential energy), both internal and external, that act on a quantum particle, along with the initial conditions of the system--quantum theory cannot produce a single answer to any question you might pose, but only a list of possible answers, along with the probabilities that a measurement of the relevant physical quantity will produce each possible result.
For example, if I ask "In my particular experiment, what is the magnitude of the orbital angular momentum of the electron in a hydrogen atom", quantum theory will produce a list of (say) 5 possible values, along with the probabilities of obtaining the 5 values: 2%, 10%, 76% 10%, 2%--when you make the measurement. Thus, after the measurement, the angular momentum has a definite value; but before the measurement, the most we can say is that the electron will be found in one of those states, according to the weighted probabilities.
But, that is a lot of words; so, the phrase "quantum superposition" was invented to mean all of that. The common phraseology is to say that "prior to measurement, the electron is in a superposition of these 5 quantum states".
(2) The math way to say exactly the same thing is the state function (i.e., the solution to Schrodinger's equation for the given potential energy function) is a function that is a superposition (a sum) of so-called "basis functions" (or "basis states"); each basis state is one of the 5 states mentioned above.
This is what people mean when they write things like "the electron can be in two places at the same time", but it is a horribly imprecise and misleading way to phrase it. --But I understand why writers do it; look how many words it took me; what newspaper editors would allow 400 accurate words when 40 semi-accurate words will sort of do, and who the hell besides a few physicists will care, or even know?
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One difficulty is that the observation of the interference patterns of double slit experiments with even single photons demonstrates the superposition of quantum states in a macroscopically observable way. It's very difficult to explain or understand the interference patterns of single photons fired through a double-slat experimental array without assuming that the individual photons do, in fact, have multiple locations.
The mathematics is fascinating: I've not explored for decades, but remember well my surp
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Re double-slit, I've always wondered how they can measure a single photon AND have it pass through the slit. Why isn't the photon consumed in the process of measuring it?
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I mis-spoke. The experiment typically involves electrons, not photons.
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AFAIK the experiment typically involves photons.
Not that this is relevant to my question...
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It is. The point is that if you measure which slit it passes through, the interference pattern that implies that it passed through both AS A WAVE, not a particle, disappears. The rule for this sort of thing is that if you measure wavelike properties, you don't get a definite particle position/state. If you measure a definite particle position/state, you don't get wavelike behavior any more. This is called complementarity and is the basis of the uncertainty principle. Electrons and photons alike behave
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Thanks, but the one thing your comment does not do is answer my question :-).
It is [consumed].
So then why do we see *anything* at the detector screen when measuring at the slits? How do you measure a single photon passing by without consuming it?
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OK, I'll try again. YOU DON'T. All you see is electrons being "consumed" as they hit the screen, forming the interference pattern.
If you DO look for them as they pass through the slits -- where one can do this without "consuming" them by e.g. putting a conducting loop around the slit that will experience a voltage pulse as the electron passes THROUGH it or by illuminating the volume right behind one of the slits with intense light that can scatter off of the moving electron and hence detect the slit the e
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e.g. putting a conducting loop around the slit that will experience a voltage pulse as the electron passes THROUGH it
Thanks.
Experimental setup (Score:2)
In an over simplified-way that might make physicist angry... ("I am a doctor, Jim ! Not a quantum physicist !")
Design a machine that fires approximately 1 photon per second.
Measure and confirm rate of photo firing.
Then put double slit in front.
Expose picture.
As during any given second, there's (an avarage) maximum of only photon,
then (in average situation) this single photon should not have any other to interact with.
Classic physics should predict only a (predominant) picture of the slit with (nearly no) pa
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This is what people mean when they write things like "the electron can be in two places at the same time", but it is a horribly imprecise and misleading way to phrase it.
Yah, I wonder if they said something like "the electron could be in either of two places at the same time" instead if that could be more easily understood (if that phraseology doesn't break the idea of superposition in the first place).
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Re:Physics breaking things (Score:1)
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Oh, physics breaking things. I'm so scared. Wait, no I'm not. What have you got against "physics breaking things"? From what I've been able to figure out however is that nothing, electrons included, are all that well defined.
And that is where you fail. Science will never claim to know everything. But it is indisputably the best way to shrink-wrap the tightest boundary about what things we do know.
That is all. [mic drop]
Re:Where I fail (Score:1)
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Looking at this thread again, I am inclined to concede graciously. You and I may very well share the same take on reality.
My point was that science is not infallible, but that it is the best tool we have for understanding the universe. And whatever counter-intuitive theories we come up with must be accepted if they fit the data. And that means that electrons are very well defined by our current theories, even if it means they can be in two places at once.
Peace out.
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Sometimes 2 ore more theories may explain the data equally well
Theory on faster than the speed of light (Score:1)
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Sorry, I wasn't clear: I'm not suggesting the other interpretations of QM are nonsense; I am suggesting that the statement that "the electron could be in two places at once" is nonsense. As the poster below me said, there are NO interpretation of QM (of which I am aware) that will make that claim.
(That said, the Copenhagen interpretation, whatever its ontological problems, has the virtue of having stood the test of time and--more importantly--LOTS of experiments.
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Many interpretations are that it is actually a wave, and not a particle at all during travel. So it isn't "two places at the same time" so much as it is a wave. From the perspective of this wave though travel is instantaneous (time does not pass), so its not breaking a law being a particle at one place, a wave during the travel, then a particle at the end point.
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The classic double-slit experiment says otherwise; if you pass one electron at a time through the apparatus, and you get an interference pattern, that means the electron passed through both slits (i.e. it was in two places at once), and interfered with itself.
Nobody explains this in a way that makes sense (Score:1)
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You have lots of electrons, but only one at a time.
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heard of it. How would I be saying that nobody explains the experiment in a way that makes sense if I hadn't heard of it. You have some serious reading comprehension issues.
Re:And again people sound off... (Score:1)
Re:Lack of detail (Score:1)
Not worth arguing over [Re:Lack of detail] (Score:1)
There are different models to "explain" quantum physics. Some versions imply things can indeed be in two places at once. For that matter (no pun intended), what is a "place" and "at once" exactly? English wasn't meant to be precise enough for sub-atomic behavior.
Re:Not worth arguing over (Score:1)
Re: (Score:1)
The classic double-slit experiment says otherwise; if you pass one electron at a time through the apparatus, and you get an interference pattern, that means the electron passed through both slits (i.e. it was in two places at once), and interfered with itself.
That's bovine fecal matter. You do not detect an interference pattern. An interference pattern would be the envelope of a very large number of detection events. You would only have one detection event. xkcd hails your extrapolation skillz [xkcd.com]
Next, your understanding of the Young experiment is lacking. It might have helped if you did this in a Physics lab. Or wrote the wave equations, to realize the factors that drive the interference pattern's shape. You might otherwise be surprised to find out that if you pass
Re:Magical thinking (Score:1)
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I haven't seen any evidence to suggest anyone has actually measured an electrons location and velocity at a given time to absolute accuracy. That's a problem I have with much of the surrounding physics claims.
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Mathematically? It's because the function that produces the probability values is time-dependent; the result is that the probabilities of the various values (momentum [not velocity] and position, to take your examples) change over time. Thus, if you wait too long after you made your first measurement, subsequent measurements of the same physical quantities will have "decohered" again.
Physically? Since there are lots of possible quantum states, and since the probabilities associated with those states are det
Re: (Score:1)
Then explain the double slit experiment. Why the sinusoids interference pattern?
Re:What might be happening (Score:1)
Looks like it's time for "the talk" (Score:3)
No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.
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*Technically, the square modulus of the wave function.
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Sorry for the physics rant; I feel better now.
The good ole story of what happens when two particles feel really entangled.
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No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.
That doesn't really explain the crazy part of QM, it just sounds like a particle bouncing around to form the probabilities, like saying Schrödinger's cat is dead or alive long before you open the box. What's so hard to understand is that it's not just passive observation, the act of observation collapses the wave function. The opening of the box decides if the cat is alive or dead. I think in laymen's terms you can't explain an uncollapsed wave function any more correctly than that a qubit is both 0 an
Part of the problems with describing quantum... (Score:1)
So qubits apparently involve encoding of functions, not just states.
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Correct; I was attempting to explain what, not why. To the best of my knowledge, the question of why an observation collapses the wave function has only been partly answered. Essentially, you have to ask (for every case) exactly how the observation was done. Most commonly, you bounce one or more photons off of the thing you want to observe (or you arrange for it to emit on or more photons). This appears to be the cause of the collapse. Hopefully someone who knows more than me will chime in with more detail?
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You will find that the interference pattern is destroyed! You will instead get two blotches of electrons, one in front of each slit.
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No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.
Well, according to the standard interpretation of the theory, that is itself only a model of what we think the world seems to be like. What QM has to say about the subject could also be interpreted as "particles are not actually points in space, and what we see may be an artifact of the way we measure things"; not the orthodox view, I know, but I think it is healthy to try to find a path away from the current orthodoxies, not least because we know that our theories are incomplete. Unless things have moved a
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Hey, somebody had to do it. Using English with embedded classical logic to describe quantum phenomena is a waste of time. And even most physicists have never read Schwinger or studied the Nakajima-Zwanzig equation and hence have little idea of how to formally obtain the classical measurement projection in an open system interacting with a classically described statistical bath when the combined closed system is in a stationary state and has no probabilities at all. And then there is relativity and time r
WARNING: Geekiest joke ever dropping here (Score:4, Funny)
LIGO my EGO!! [wikipedia.org]
Re: (Score:2)
An ego big enough to generate gravity waves? Hmmm, who could that be?
Well of course. (Score:1)
At least what you say makes sense. (Score:1)
Your statement makes sense, and is pretty much topical and if people feel they don't understand it, could stand to read it several times until they get a better understanding. Better yet they should take a moment and think through what a good question might be and ask it.
Re:Well, what would be different? (Score:1)
1. It would take more than eight minutes for changes (caused by its motion around the Milky Way galaxy) in the sun's gravity to reach the earth and even longer for the more distant planets.
2. So the earth's orbit around the sun would depend on where the sun was eight minutes ago, the time it takes changes in the gravitational field to reach the earth, and not on where it is now.
3. This is not observed.
So how is what would be observed given 1 and 2 be different from what is observed?
Re:Clocks (Score:1)
Re:Time not a dimension (Score:1)
Now you border on something that begins to make sense with the only one speed bit, but here is an observation for you: An object at motion is also an object at rest.
Re:Your AI nonsense (Score:1)
Gordon doesn't need to hear all of this. (Score:3)
Finally, quantum theory and gravity unified! (Score:2)
Comment (Score:2)
This topic sounds like a Star Trek episode. Think Star Trek: Voyager where the crew has to rescue a planet from itself because they were experimenting with gravity waves!