Gravitational quantum detection

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drag

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Greetings !

I remember posting a partially(I intend to add a different
more profound example, if I get some feedback on this enitial
message) similar thread here before called "gravitational
double slit", but for some reason I couldn't find it.

Anyway, basicly I was asking wheather physics can answer
the following question today (or at least what is the majority
opinion on this issue) :
What would happen if gravitational waves were used instead
of electromagnetic waves to detect the quantum in the
double slit experiment ?

Would there be a "detection" ? Would it collapse the WF ?
Would the HUP be violated if the first answer is yes and
the second is no ?
(At least make your best guess. :wink:)

Live long and prosper.
 

selfAdjoint

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Gravitational waves ought to diffract, and self-diffract. You would have to use a BIG slit though.

Note: Gravitational waves are not the wave nature of the graviton.
 

drag

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Greetings !
Originally posted by selfAdjoint
Gravitational waves ought to diffract, and self-diffract. You would have to use a BIG slit though.

Note: Gravitational waves are not the wave nature of the graviton.
I think we've had a slight misunderstanding. I'm not talking
about any gravitons or hypothetical theories of
"GR + QM". I'm talking about a "normal" double slit experiment
with photons/electrons/whatever where the detector/s at the
slit/s uses gravity waves. (Abviously this is by far
outside of the range our current technological capabilities
but that does not invalidate the question :wink:).

Thanks ! :smile:

Live long and prosper.
 

jcsd

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gravitaional wwaves pass through pretty much everything so your not going to be able to diffract one. A gravitational wave is the result of a dynamic gravitational system.
 

marcus

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Originally posted by jcsd
gravitaional wwaves pass through pretty much everything so your not going to be able to diffract one. A gravitational wave is the result of a dynamic gravitational system.
tho with all possible good will, nevertheless no one is understanding drag's question

feynmann discussed a thought experiment where one tries to
"fool" the double slit experiment by putting a detector by
one slit so one can catch the electron in the act of going thru the slit

putting a detector destroys the interference pattern
so nature forces you to take the detector away or else she
refuses to do her thing

NOW DRAG SAYS what if you made a detector of photons or electrons that works by feeling the gravitational field have
a little spasm when the electron goes thru the slit
and by the wonders of technology this detector is very small (!)
and can be put beside just one slit (!!!!)

then drag says, wouldnt this be a way of spying on nature and
finding out which slit it went thru without disturbing the fringes
or some such thing---i dont quite understand

this really is one for selfAdjoint or for jcsd
it is a feynmannesque thought experiment so cheers to you drag
but the answer is likely that no you could not use it to tell which slit (or if you set it up so you could the pattern would go away)
 

jeff

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Originally posted by drag
What would happen if gravitational waves were used instead
of electromagnetic waves to detect the quantum in the
double slit experiment? Would there be a "detection" ? Would it collapse the WF ?
Would the HUP be violated if the first answer is yes and
the second is no?
The double slit experiment demonstrates that particles have a wave aspect, and in particular, a debroglie wavelength, given by hbar/p where p is it's momentum. I don't see why detection gravitationally would produce a different result than detection by a geiger counter, or any other suitable detection device for that matter.
 

drag

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Greetings !

Well, marcus finally (I actually thought that what I said
was quite clear but I appologize if I were mistaken)
pretty much understood me. Although I have to say he
really exhagerated somewhat - it's just a hypothetical
question (for now) I didn't say we can actually do it
and I did not say I prefer some some result.

I am not quite clear as to why marcus is so certain of
the answer. A detector near one or both slits would collapse
the WF if its electreomagnetic (like in the normal experiment)
a detector using nuclear forces probably will too (even if
such experiments haven't been conducted, these forces
are parts of the extended quantum theories that have so far
proved to be correct for them).

But gravity is a different thing. In fact, if for example
our detectors will "feel" 60% of the particle passing through
one slit and 40% through the other and there will be no
WF collapse (we'll the diffraction pattern on the screen)
than not only will we know that GR and QM can not be connected
in many currently theorized ways but QM is infact incomplete
or inaccurate altogether. On the other hand we could discover
that the WF will collapse which probably means that gravity
can and should be quantified somehow. Alternativly, we could
detect 100% of the paretcile's mass passing through a single
slit but still see diffraction on the screen (no WF collapse),
thus confirming some "hidden variables" theory.

What I want to know, again, is the answer or at least the
most likely (as it seems today) answer to that (which may
be what marcus said alright).

I could also rephrase the question more clearly perhaps:
Does a partcile produce space-time curvature (as we normally
expect it to as well) when it is not interacting with other particles ?
If the answer is yes - doesn't it mean that the HUP
can be violated "through" gravity ?

Live long and prosper.
 

jeff

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Originally posted by drag
...if...detectors..."feel" 60% of the particle passing through
one slit and 40% through the other...
It doesn't work that way: A detector spying on a slit either detects a particle to have passed entirely through it, or it doesn't detect it at all.

Originally posted by drag
Does a particle produce space-time curvature...when it is not interacting with other particles?
If the answer is yes - doesn't it mean that the HUP
can be violated "through" gravity?
I think I pointed out to you the second time you asked you're question that since gravity couples to everything - including quantum fields etc. - it would be hard to see how to build a consistent QGT without gravity being governed by the same quantum laws that everything else is.
 

LURCH

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This is a very interesting question. I would have to say (and this is only my guess) that I think the presence of a detector, even a GW-based detector, would still alter the pattern on the detection plate at the end of the experiment. And my reasoning is this;

It is a predicted quality of gravity waves that they carry energy away from any phenomenon that generates them. At the quantum level, where wave/particle duality becomes significant, the difference between energy and matter gets hazy. So I think that any thing that carries a detectable amount of energy away from a particle must alter that particle. Which, I suppose, brings up another rephrasing of your question,
Does a partcile produce space-time curvature (as we normally
expect it to as well) when it is not interacting with other particles ?
I would say that if there is a gravity wave to be detected, then the dispersion pattern will be altered. And if there isn't, the interference pattern will be produced at the end of the experiment, but the detector in or near the slit will detect nothing.
 

selfAdjoint

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I agree with you Lurch. I think if there is an interaction with the particle - some exchange of virtual bosons - then the particle is "pinned down" in the sense that its location is established(up to uncertainty) as being at one slit rather than then other, and it can't any more exhibit waviness because localization like that is not consistent with a wave encountering both slits.
 

drag

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Greetings !
Originally posted by jeff
It doesn't work that way: A detector spying on a slit either detects a particle to have passed entirely through it, or it doesn't detect it at all.
Have you ever heard of a working gravitational particle
detector of this scale ?
I'd love to see the design. :wink:
Originally posted by jeff
I think I pointed out to you the second time you asked you're question that since gravity couples to everything - including quantum fields etc. - it would be hard to see how to build a consistent QGT without gravity being governed by the same quantum laws that everything else is.
For the moment I'm not trying to do anything but try
to receive the most likely answer to a question.
Also, you'll agree with me that for the moment we see
that gravity is NOT quantified in any way what so ever
(as far as I've heard at least) and while I'm not trying
to defy QM, it is, in my opinion, quite reasonable to assume
that to find the connection between these two foundations
of modern physics we should not just think of new mathematics
but also of new revolutionary experiments.

Peace and long life.
 

jeff

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Firstly,

Let me just say that your line of questioning from my point of view is just about the most interesting in the forum at the moment.

Originally posted by drag
Have you ever heard of a working gravitational particle
detector of this scale ?
Star Trek the next generation, episode sixty nin......Oh, you probably mean for real, right? My feeling is there's at this point no theoretical reason to doubt that such a thing is possible in principle and that it would operate analogously to any other kind of detector.

Originally posted by drag
...for the moment we see
that gravity is NOT quantified in any way what so ever...
Empirically yes, but the theoretical picture makes a strong - irresistable in my view - case for quantizing gravity.

Originally posted by drag
it is...reasonable to assume
that to find the connection between these two foundations
of modern physics we should not just think of new mathematics
but also of new revolutionary experiments.
Yes, we must try our best.

Let me ask, are you thinking that perhaps gravity need not be quantized, or that gravity may undermine quantum mechanics vis a vis the uncertainty principles?
 

drag

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Greetings !
Originally posted by jeff
Firstly,

Let me just say that your line of questioning from my point of view is just about the most interesting in the forum at the moment.
Thanks. :smile:
I was wondering why my previous thread about this
was so "dull".
Originally posted by jeff
Empirically yes, but the theoretical picture makes a strong - irresistable in my view - case for quantizing gravity.
I'm no expert, but I've heard of a recent attempt, for example,
that failed. They tried to detect gravitational quantization
by observing very distant objects like quasars and looking
for distortions, but failed.

As for wheather the HUP can be violated, personally I do
not think so, 'cause it would seem to me that this is
not just a limmit but rather a fundumental border. Of course,
I'm really totally not qualified to judge on the matter. :wink:

As for gravity being quantized, again my personal insignificant
opinion is that it won't happen, at least, not in the
standard manner in which the other forces were quantized.
(If I weren't an atheist, I'd say that God loves riddles. )

Live long and prosper.
 

drag

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Greetings !
Originally posted by Lurch
This is a very interesting question. I would have to say (and this is only my guess) that I think the presence of a detector, even a GW-based detector, would still alter the pattern on the detection plate at the end of the experiment. And my reasoning is this;

It is a predicted quality of gravity waves that they carry energy away from any phenomenon that generates them. At the quantum level, where wave/particle duality becomes significant, the difference between energy and matter gets hazy. So I think that any thing that carries a detectable amount of energy away from a particle must alter that particle.
Well, I suppose I could try to argue that a space-time
wave may be completely different in its effect, but
I won't. Besides, considering quantum limmitations on
sensitivity I suppose there wouldn't be a way for us
as observers (if not the experimental particle) to
escape the HUP during the entire experimental process.

HOWEVER, there is something else I believe I can see here.
GR is not a quantum theory, it is a theory of geometry
(that Einstein preffered and liked) hence, theoreticly,
we may not even need any machine creating waves in space-time
through very intense gravitational interactions. Basicly, we
could just put something there and see if it gets attracted.
Now, if I'm not mistaken, the HUP should have no effect here
because it's not even a quantized interaction - rather a
"continuos" geometry change the scale of the observation of
which we can then increase(not enough though :frown:). For example, suppose that I send the same particle through two very long tunnel
like slits - the gravitational attraction should become
more apparent - wheather the WF will collapse or not and
if there will at all be some attraction.

In fact, the more I come to think of it as I write - let's
consider wheather this IS a technologicly possible experiment
TODAY:
We run the double slit experiment, the slits are turned
into long narrow (according to the wavelenght) tunnels
one above the other and the particles (say electrons) are
injected at very relativly low speeds. Now, we allow the
tunnel slits to be capable of detecting an electron impact.
Then we run the experiment for a great deal of them and
see wheather amongst the electrons that did not emerge
from the tunnels and were detected there, a greater, by some
degree, amount impacted the lower walls of the tunnels
slit and a lesser amount impacted the upper walls.
Thus we might just be able to see wheather the uncollapsed
WF "flows" in accordance with space-time or just the other
3 forces we've already quantized.
So, does the above make any sense ?

Further more, if I am nor mistaken this could even have
ramifications for the Equivalence Principle, since we know
that if the same occured in a "normally" accelerating frame
the WF will feel the acceleration, right?
Originally posted by selfAdjoint
I agree with you Lurch. I think if there is an interaction with the particle - some exchange of virtual bosons - then the particle is "pinned down" in the sense that its location is established(up to uncertainty) as being at one slit rather than then other, and it can't any more exhibit waviness because localization like that is not consistent with a wave encountering both slits.
But, aren't you assigning quantum propeties and behaviour
to gravity ? If I'm not mistaken, it has so far refused
to work according to such models, or am I indeed mistaken ?

Well anyway, I'd really appreciate your responses and I'd
like to remind you, again, that I'm not claiming anything
or am specificly in favour of some option, I'm just trying
to examine them in general and make some general sense of
the question, and the rest is a matter for you the experts to
decide upon. (Though if it's possible, I'd appreciate you telling
me at which stage I should either start copyrighting or go do something more useful like water some plants or somethin'... )

Live long and prosper.
 

drag

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Oops... :frown: Sorry for that one, I thought about it the
next day, but I couldn't get online since then. The above
experiment, of course, would not test what I wanted
to find out. It would test wheather the WF follows space-time
curvature (geodesic lines) which, I believe, is almost
certainly known as the case, rather than test wheather the
WF itself would create space-time curvature - which is
the object of my inquiry.

Anybody care to make suggestions as to technologicly possible
experiments or some comments on the matter ?

(One abvious possibility is to trap an intense laser beam
between two mirrors and see wheather the medium in between
produces graviatational pull - but, abviously, that would require
"slightly" more accurate instruments than the ones availible to
us today. :wink:)

Live long and prosper.
 

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