Re: What's up with gravity wave detection?
From: Eric Flesch (eric_at_flesch.org)
Date: 08/31/04
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Date: Tue, 31 Aug 2004 20:07:13 GMT
On Tue, 31 Aug 2004 01:47:02 -0000,
dubious@radioactivex.lebesque-al.net (Bilge) wrote:
> You didn't address the fact that light is a four vector, which for
>whatever reason, you seemed to think was an essential feature.
T'was you who used that term to describe light, not me, and in any
event the four vector relates to spacetime transforms which is not my
point which is regards to the nature and behavior of the individual
photon.
> Eric Flesch:
> >(two books on QG) are speculative works.
>
> In what way do you find them speculative? In view of the fact that
>you specifically referred to qed, which is a quantum field theory,
>try to be specific.
I was specific, but you snipped that part. My whole reply was:
"These are speculative works. What has quantum gravity ever predicted
which has been observationally confirmed? (which is the topic of this
thread)" To that I will add that they present progress-thus-far on an
experimentally unverified hypothesis. Specifically, the "graviton"
does not exist and so will never be found. I do however think that
gravitational waves should be detectable, but they have no particle
analog. I expect the tension of the universal brane would dampen
gravitational waves from far-away places to where they do not reach
us. Too much is made of the "similarity" of gravity and light, when
gravity is likely, instead, to use a 4th spatial dimension to
propagate in addition to the usual three. OK, is that specific enough
for you? (and off-topic to my original point, altho perhaps more
on-topic to the thread title)
> >A pity fhen that photons don't travel in continuous paths, shown by
> >the delayed-choice experiment.
>
> That is not what that experiment shows and in any case, what does that
>experiment have to do with anything?
It shows that GR stress-tensors do not model photon behavior and so
cannot be used, as they so often are, to claim that the in-flight
photon exerts gravity.
>You mentioned qed, so obviously you
>must think special relativity is ok. How does formulating qed in curved
>spacetime differ in any way from formulating it curved spacetime with
>a specific value for the curvature, nanely zero, in any way that matters
>to your argument?
It makes no difference, I suppose. You're obviously very learned and
skillful, Bilge (you could have picked a nicer nick), but physical
models are just descriptions. Think of the reality of being a photon.
You are emitted from place A. You are absorbed at place B. And what
is your experience in between? You are travelling at the speed of
light, you know. What is the time dilation involved? Did you not
have time to view the passing scenery? No time to exchange gravitons?
This is the point, the in-flight photon has *no time* to interact with
spacetime whilst on its journey. There is no classical existence
whilst travelling at c. No continuous travel, no precise vector. The
photon can only depart and arrive. Its experience is that of stepping
across, analogous to conduction between bodies in contact. And the
wave description of its flight is the mapping of that vectorless
conduction into our 4D spacetime manifold. Model that, "Bilge".
> All you've quoted is
>an ancient and irrelevant thought experiment about quantum mechanics.
>Stop jumping from topic to topic.
I was replying to Carlip's "demonstration" that light is attracted to
mass, showing that gravitational equivalence to time flow accounts for
it. Never mind, then.
> No one, least of all me, is disputing quantum mechanics. I'm disputing
>your understanding of quantum theory and general relativity, not to mention
>qed.
I'm not a professor of QM as you appear to be. Your knowledge is
greater than mine. That doesn't prohibit that I might have a correct
thought which you did not yourself arrive at. Think about it. There
are problems with current theory, such as the inability to unify QM
and gravity. Is it not sensible to investigate changes in the model,
consistent with observation, which might bring that unification
closer? Any simplication is bound to be favorable. My idea on light
is a simplification.
> >I expect (ignoring neutrinos) that the box will weigh less the more
> >"in-flight" radiation there is inside the contained box, so W(1)=W(3)
> >and W(2) is less. Do tell me about any such experiment which has been
> >done -- citation please.
>
> In other words, what you are saying is that energy, momentum and
>angular momentum are not conserved.
It depends on what frame you use. The key is what the null geodesic
represents. It is, in fact, the straightest of lines. When spacetime
is bent by a mass, you (presuming your thought is similar to others'
in your profession) seem to think that there is a "straighter" line
than that, by which the curvedness of the geodesic can be described.
But what is spacetime curvature all about, other than a redefinition
of straightness in local places? We can view the curvature from a
distance, but even our lines of sight follow those geodesics.
If we take the gravitational contours to represent true straight
lines, then angular momentum is still conserved. But this would lead
to some interesting results, it is true. Using advanced technology,
we could build this device:
Say we can construct a pinhead-sized black hole using electrical
current (so it evaporates when the current is shut off). We place
this in the engine room of a spaceship. Now we release photons at it
at such a trajectory that they go half-way around the black hole and
come back with a return vector opposite to the emitted vector. That
means we have double recoil in one direction only. We could move our
spaceship without any external emission.
Ridiculous? Remember that any sufficiently advanced technology seems
like magic to learned men of a previous era. Think about it.
Eric
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