Gravity-Detecting LIGO Also Found To Be Creating Gravity Waves (sciencemag.org)

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."

Comments

Gravity wave != Gravitational wave

[skoskav]

Hopefully I ruined the fun by being pedantic.

Re:Gravity wave != Gravitational wave

[TeknoHog]

Let me wikipedia that for you:

https://en.wikipedia.org/wiki/... -- waves on the surface of water whose dynamics is dominated by gravity. See https://en.wikipedia.org/wiki/... for smaller ripples dominated by surface tension.

https://en.wikipedia.org/wiki/... -- what the fucking article is about

Copenhagen Interpretation

[jIyajbe]

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.

----------------

*Technically, the square modulus of the wave function.

----------------

Sorry for the physics rant; I feel better now.

Re:Copenhagen Interpretation

[jIyajbe]

(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?