Entanglement Makes Quantum Particles Measurably Heavier, Says Quantum Theorist 109
KentuckyFC writes: Physicists have long hoped to unify the two great theories of the 20th century: general relativity and quantum mechanics. And yet a workable theory of quantum gravity is as far away as ever. Now one theorist has discovered that the uniquely quantum property of entanglement does indeed influence a gravitational field and this could pave the way for the first experimental observation of a quantum gravity phenomenon. The discovery is based on the long-known quantum phenomenon in which a single particle can be in two places at the same time. These locations then become entangled — in other words they share the same quantum existence. While formulating this phenomenon within the framework of general relativity, the physicist showed that if the entanglement is tuned in a precise way, it should influence the local gravitational field. In other words, the particle should seem heavier. The effect for a single electron-sized particle is tiny — about one part in 10^37. But it may be possible to magnify the effect using heavier particles, ultrarelativistic particles or even several particles that are already entangled.
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You can't hover over links before you click them?
Particle physics is easy ... (Score:4, Funny)
We only need to measure the mass of a 9.10938291 × 10^-31 kilogram particle accurate to 1 part in 10^-37. Alternatively, we can speed the electron up to 0.999c so it weighs more, then entangle it, and then measure it's mass to 1 part in 10^-37, with less than 5 sigma of measurement error.
Either way, I should have it done by lunch time.
It's even easier (Score:2)
[...]Either way, I should have it done by lunch time.
I see you've read the article, so can you explain something for me?
I'm told that photons gain energy when falling into a black hole. Suppose you have two entangled photons and one goes off and gets captured by a black hole.
Based on the article, would there be any noticeable effect on the other entangled photon?
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It's kinetic energy increases, but its mass stays constant (exactly 0), as does its total energy (since it loses gravitational potential energy as it gains kinetic energy).
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Excuse me? E^2 = p^2c^2 + m^2c^4 is the correct statement (or to be pickier, the four vector P = E/c - \vec{P} has conserved length equal to mc). Photons have zero mass, so for them E^2 = p^2c^2. You are thinking of E = \gamma m_0 c^2, which works fine for massive particles where m_0 \ne 0, not so well for light where \gamma = \infty because light travels at the speed of light.
BTW, does /. grok latex if one wraps it, that is, does $$E = \gamma m_0 c^2$$ work? Might as well try it...
No, apparently not.
Momentum, not mass (Score:5, Informative)
The photon has zero rest mass, yes.
E = mc**2 is a nice popularization; it's also wrong. It's actually E**2=(mc**2)**2 + (pc)**2, where p is the momentum. When momentum is zero, you can usually simplify this to E=mc**2, but a photon's existence is defined mostly by its momentum. Since m is zero for a photon, this means the energy of a photon is given by entirely by E=pc.
Hope this helps!
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How do you define gravitational potential energy such that a massless particle has any?
Regardless, both this comment and the parent comment are ignoring the importance of reference frame. Relativity is not at all my specialty, but it's unclear to me how you should talk about a single photon in relativistic gravitational fields, since it's impossible to make any measurements on the photon without affecting it's energy.
Re:Particle physics is easy ... (Score:5, Interesting)
Either way, I should have it done by lunch time.
Or we could spend some time coming up with additional consequences that might allow indirect tests. For example, does this effect have any consequences for the spectrum of Hawking radiation (just to consider one area were entangled pairs and high gravitational fields are involved)?
How about the structure of the very early universe?
Or are there ridiculously subtle interferometric effects that might allow the detection of the phenomenon? Or other quantum effects?
Consider the Mossbauer Effect as an example of measuring stupidly small energy splittings so many orders of magnitude below any reasonable detector resolution that no doubt some smug bastard made fun of the people doing the hard work of calculating them "because no one will ever be able to measure that!"
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Mod parent up.
Also, perhaps further development of the theory could hint at methods of unification of QM with GR.
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Sure, and consider that we do not yet have direct experimental confirmation that antiparticles fall down, instead of up. There's a reason for that, and it is 30 orders of magnitude.
The antiparticle experiment actually might be doable. And it is the thing that is a mere 37 orders of magnitude short of measuring the difference in weight of entangled quantum antiparticles.
So yes, you are right, one cannot be certain that there is no supremely clever way to measure Planck-length scale phenomena without using
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The mass difference between an entangled cat and a non entangled cat is the mass of the tread it got entangled in.
see these images [shutterstock.com]
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You saved me from having to reply. I do not think that this "measurably heavier" means what you think it means (or rather, they think that it means), to quote Inigo Montoya. Let me 'splain. No, there is too much, let me sum up. In addition to the fact (as you have so ably pointed out) that we will never, in the future course of the universe, be able to measure the effect predicted, it is a theoretical prediction based on assumptions in a particular circumstance. If the assumptions turn out not to be co
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So you're/they're saying mass-energy in any form doesn't have a "weight"? Einstein was even wronger? Rearrangements at constant mass-energy can have different weight? At the Planck scale you can say pretty much anything you like and not have much chance of your words being falsified, and while I'm not a falsificationist and agree that a consistent hypothesis can have meaning even if it can't be verified or falsified, this falls into the same scientific category that magnetic monopoles do, only tens of or
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:-)
BTW, nice recursively demonstrative 1337 handle...;-)
rgb
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Now I know that I am just entangled.
Massively entangled.
It's true (Score:5, Funny)
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I noticed how fat yo mamma is when I got entangled with her last night.
Next Big Thing (Score:2)
So what is going to be the Next Big Thing?
What is the next Theory of Relativity waiting to be solved and what will be the game changing technology made possible by it?
Re:Next Big Thing (Score:4, Funny)
not to spoil it for you but it's time travel. i'll be making my announcement in 2044 and personally demonstrate that you can travel 5 minutes back in time. needless to say, i forgot to carry the one.
Re: Next Big Thing (Score:1)
Time travelling works fine. To prove it, I will travel back to when this article was accepted on slashdot and be the first poster. Be warned, time travelling makes me cranky and homophobic.
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How do you modify the spin of a particle without measuring it? (and how would you know the difference of whether you had measured it or not?)
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Presumably you get your pop science entirely from tabloids dear anonymous coward because entanglement has been throroughly verified by experiment. Too bad Einstein didn't live to see the flaw in his EPR paradox explained (Bell inequality).
Not "does indeed" (Score:4, Insightful)
That's a theoretical analysis, not an experimental measurement, and is likely to be particularly dubious since we don't have a working theory for quantized general relativity yet. Interesting, but the phrase "does indeed" in the summary is a significant overstatement.
Penrose gravitational wavefunction collapse (Score:1)
This sounds a lot like Penrose's proposal for wavefunction collapse caused by gravitational disturbance caused by particles being in a superposition of two locations...
Interesting use of measurable (Score:2)
Seeing as you are talking about a change in mass that is 34 orders of magnitude smaller than the Planck constant
h/2 > (delta MV)(Delta x)
(6.62606957 × 10-34 m2 kg / s)/2 > (Delta (M)*V)(Delta x)
delta M = 9.10938215kg×(10^-31)/ 10^37
or = 9.10938215kg×(10^-68)
We are looking at some pretty big uncertainty about where the particle is and how fast it's moving.
Should have searched first (Score:2)
The current uncertainty of electron rest mass is
http://en.wikipedia.org/wiki/E... [wikipedia.org]
The 2006 CODATA recommended value has a relative uncertainty of 4.2×1010
So all you need to do is add 27 orders of magnitude to the certainty of the electrons mass.
that should read 10exp10 not 1010 (Score:2)
What is with slashdot and the exponentiation symbol\
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You're right it's even worse in qm. I am curious why you didn't mention that ?
Oh hell let me put this in a way you can grasp (Score:2)
The amount of change in mass you would be trying to detect is less than what the uncertainty principle allows for the creation of virtual particles over the length of time any reasonable experiment could run. Good luck with that.
FTL communications? (Score:4, Interesting)
Given that two particles can emitted by a single source entangled, sent a long distance apart, and remain entangled,
And that if one particle becomes disentangled the other particle instantaneously becomes disentangled,
If we can measure the entanglement of a particle by its mass,
Then we can communicate faster than light.
But the no-communication theorem [wikipedia.org] states that, during measurement of an entangled quantum state, it is not possible for one observer, by making a measurement of a subsystem of the total state, to communicate information to another observer.
So I think this means that either the no-communication theorem is wrong, or the change in mass of an entangled particle cannot be measured.
Re:FTL communications? (Score:4, Informative)
So I think this means that either the no-communication theorem is wrong, or the change in mass of an entangled particle cannot be measured.
That's an interesting point, but on my reading of the paper (which was pretty cursory, admittedly) the extra mass term comes from the joint wavefunction, which means both particles would have to be measured. It looks like the pair has greater mass, not the individual particles.
This makes sense because insofar as they are entangled it doesn't even make sense to talk about the individual particles. Furthermore, if one were to measure either of the particles individually, that would break the entanglement and the extra mass term would fall to zero.
Thing of the highly idealized experiment of two sources on a balance beam, one that emits pairs of non-entangled particles, one that emits pairs of entangled particles. The theory says that the balance will tip toward the side of the entangled pairs, but it does not follow from this that measurements on any of the individual particles will reveal increased mass.
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Maybe It's Me (Score:2)
wouldn't it be cool (Score:5, Informative)
FWIW, it appears from the paper that this extra "mass" is an artifact of analyzing entangled particles in a linearized gravity [wikipedia.org] framework and observing a stress-energy tensor term that seems to appear higher for entangled particles and radiated away as particles move to decoherence. This perhaps might be considered the mass of the entanglement.
On the other hand, wouldn't it be cool if the reason for the observed equivalency of gravitational mass and inertial mass was somehow related to quantum entanglement? (yes I know this is unrelated to this phenomena, but still)...
Re:wouldn't it be cool (Score:4, Funny)
Right? I was just gonna say that.
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Is it really a motional term (i.e., due to a higher level of quantum jitter)?
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Dude that would be so cool!
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I looked at the paper and i have the feeling that they misuse the term "entangled". At least their definition of the density operator seems dodgy. If they would not say it's entangled i would call it a superposition state of a single particle.
Which, in terms of the density matrix is not so different. But we experimentalists usually require two particles with multiple states to use the word "entanglement".
Moreover, since they are comparing a mixed state, i would find it particularly interesting if there is
Not (Score:3)
One part in 10^37 is not measurably heavier. No measurement in science has anything like 37 significant figures*.
*No, the cosmological constant does not count, as it was not measured from quantum principles, but from cosmological ones.
I'm not fat... (Score:2)
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Holy Fucking WRONG (Score:3)
The discovery is based on the long-known quantum phenomenon in which a single particle can be in two places at the same time.
Wrooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong.
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The discovery is based on the long-known quantum phenomenon in which a single particle can be in two places at the same time.
Wrooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong.
Right. The long-known phenomenon is that a single particle can have two velocities at the same time. Sheesh.
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It doesn't "behave" in any way until you interact with it. It doesn't exist "in two places at the same time".
And (Score:3)
Leon's getting larger.
encryption (Score:2)
Didn't RTFA, but still wondering: does this mean quantum encryption can be beaten by adding a "weight scale" to the transmission link?
I'm not fat (Score:1)
I'm just really quantumly entangled.
not real (Score:1)
It takes about 8 minutes for the gravity from the sun to reach the earth, but quantum phenomena would travel instantaneously.
Different things.
That's a little anecdotal, but all truth is on some level.
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I would expect quantum and gravitational effects to travel at the same speed viz. Ockham's razor.
A more complex explanation could model it, but something more would be needed to persuade me.
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Only one of the meter or the second can be independently uncertain.
Yes you're right I was thinking of mass (or force). In any case, the choice of which units to define and which to measure is arbitrary, so it makes sense to define the ones we have the least ability to measure.
Cesium has been pushed down to a relative uncertainty of 10^-14sec/sec
Which is a mind-blowing achievement, I think, but it's still a far cry from 10^-37.
However this only applies to direct measurement: A cesium clock's output frequency is stable enough that the GR-induced change in frequency due to raising it one meter higher, for example, is directly measurable because that change is larger than the random wander.
That's also amazing, and maybe there's a way to test this "entanglement makes particles heavier" idea, but we still aren't going to get measurements of anything down to 10^-37 that way. You mentioned "one meter higher",
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"decimal places" should have been "significant digits".
Turns out the parent post was only accurate to within its first 44 characters.
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Sure we can.... Light years....
No, we can't. Think about it for a second ;-)
Re:Uh No (Score:5, Insightful)
The size of the visible universe is only on the order of 10^9 light years, so that won't do it. But combine it with the range of the weak force, which has been measured and our direct measurement capability spans a range of about 10^39 (weak force ~= 10^-18 meters, lightyear ~= 10^12 meters, visible universe ~= 10^9 lightyears) so we can at least comprehend this number in a concrete way. Measuring it even indirectly... not going to happen with your basic bathroom scale. But we are talking about finding a way to relate effects on the Planck scale to the cosmogical scale so big exponents should be unsurprising. Unlike the outspoken AC above I will wait for peer review before adjusting my bullshit meter. Naturally, we all want to believe there is some big breakthrough here after the endless low calorie diet of contrived mathematical attempts to unify the big theories for the last too many decades. Is this one it? Seems unlikely just based on the long run of failed attempts. But I will just sit back with popcorn and enjoy the show. At worst, a refreshing break from the usual multidimensional mathematical salad parade. I'm particularly interested in more eplanation of how two entangled particles became one, at least according to the press.
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We can't measure anything using any instrument anywhere to a precision of 1/10^37th. Bullshit meter is off the charts
We can't make any single measurement which contains 37 digits and have each of those digits accurate, that's true.
Just out of curiosity, how do radios work? I'm told that the measurement units for an antenna nanovolts per meter. Does the receiver make a 12-volt measurement to 8 digits of accuracy in order to recover the signal?
Or does the receiver amplify the signal so that it's large enough to be readily detected?
And is there no way to make multiple measurements so that the effect adds up? Can we do a mill
Re:Uh No (Score:5, Interesting)
Your question doesn't have a simple answer, but if it did, it would involve signal-to-noise ratio within a given bandwidth. A radio receiver with a bandwidth in the audio range (~10 kHz) can amplify a signal by about ten trillion times its original power or a few million times its original voltage, before hitting the thermal noise floor of -174 dBm/Hz. These figures aren't exact (for one thing, they neglect the impedance change from a 50-ohm antenna input to an 8-ohm speaker) but the basic idea is correct: the noise floor at 25C in a 50-ohm system is -174 dBm/Hz + 10*log(bandwidth) dBm.
You can improve SNR by making your measurement near absolute zero, but you can't get rid of the noise entirely because some of it isn't strictly thermal in nature. Synchronous demodulation can let you recover information from below the noise floor, given a carrier of known phase. There are other tricks and hacks, but the bottom line is that you are still going to be at least ten or fifteen orders of magnitude away from being able to work with 37 significant figures in any real-world physical measurement. Integration times for such a measurement would have to approach heat-death-of-the-Universe durations.
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Radio receivers work through several mechanisms. First, you have an antenna that is only sensitive to a certain frequency range (but highly sensitive in that range). Then you have some kind of tunable resonant circuit that narrows down the range of frequencies even further, ideally to just the single frequency band you're looking for. When radio reception is good, the signal/noise ratio in that band is quite large, even if the signal is weak. That is, the radio signal is overwhelmingly the most powerful thi
Misapplied Bullshit meter (Score:2)