Re: Questions about the Equivalence Principle (EP) and GR
On Sunday, February 24, 2019 at 6:52:50 AM UTC-7, Philip Thrift wrote: > > > > On Saturday, February 23, 2019 at 6:04:15 PM UTC-6, agrays...@gmail.com > wrote: >> >> >> >> On Saturday, February 23, 2019 at 6:53:09 AM UTC-7, Philip Thrift wrote: >>> >>> >>> >>> On Saturday, February 23, 2019 at 7:25:21 AM UTC-6, John Clark wrote: On Fri, Feb 22, 2019 at 11:08 PM wrote: > *In GR, the paths are determined by geometry in the absence of > forces, not by mediating particles.* Yes, that's because General Relativity is a classical theory that is not quantized, it has so far passed every experimental test posed to it with flying colors but we know it can't be entirely correct because when we ask it what happens when things become very small and very massive, such as in the center of Black Holes, it gives the absurd answer of infinity. Neither Quantum Mechanics or General Relativity works when things get massive and small, perhaps quantizing General Relativity will fix this or maybe there is some other way to do so. Nobody knows. > *I could be mistaken, but I see gravitons as being part of a > distinct theory of gravity, which might give the same results as GR,* Nobody has ever experimentally detected a graviton and it's extremely unlikely anybody ever will, so if they make the same predictions as standard General Relativity there would be no point in introducing the idea. John K Clark >>> >>> If all experiments proposed to determine if gravity is quantized* fail* >>> >>> Such measurements, they say, could enable them to uncover the quantum >>> nature of gravity and determine whether or not gravity is quantized. >>> >>> >>> >>> https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.122.071101 >>> >>> >>> that is: the search for a quantized gravity is a wild goose chase >>> >>> what do theorists do then? >>> >>> (I asked Hossenfelder. No answer.) >>> >>> - pt >>> >> >> *The article you cite indicates increasing hypothetical sensitivity for >> measuring gravity for tiny effects. If gravity can be quantized, what >> exactly would be quantized? Bruce says that gravity waves would involve >> gravitons under a quantized theory. Is that all? AG * >> > > > > > I suppose it needs to defined *what an experiment would be* that would > determine that gravity is quantized in a measurable way. > > Theories disconnected from experiments are mere math games. > *A good theory gives pointers on what to measure and how. AG * > > - pt > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: Questions about the Equivalence Principle (EP) and GR
On Sunday, February 24, 2019 at 5:31:35 PM UTC-6, agrays...@gmail.com wrote: > > > > On Sunday, February 24, 2019 at 6:41:00 AM UTC-7, Lawrence Crowell wrote: >> >> On Friday, February 22, 2019 at 4:40:31 PM UTC-6, agrays...@gmail.com >> wrote: >>> >>> >>> >>> On Friday, February 22, 2019 at 1:34:31 PM UTC-7, Brent wrote: On 2/21/2019 10:47 PM, agrays...@gmail.com wrote: > *Even if gravitons are detected, and they account for "force" consistent with the other three forces, wouldn't there remain the task of changing the form of gravity to make it covariant? AG* Gravitons, as quanta of the metric field, are already relativistic particles and covariant. >>> >>> *I thought it's the equations of motion for the particular force, not >>> the mediating particles, that must be covariant. On a related topic for >>> this thread, where does GR depart from Mach's principle? That is, what did >>> Einstein implicitly (or explicitly) deny about Mach's principle? TIA, AG * >>> *Would that require tensors? AG* >> General relativity is covariant, and curvature is expressed according to >> Riemann tensors. >> >> LC >> > > *Thanks, but I think you missed the thrust of my question; namely, if a > theory using gravitons is independent of GR, since it would have to be > covariant, could that be done without tenors, or are tensors nevertheless > necessary. AG* > Tensors transform homogeneously with the Lorentz group and are thus covariant. Yep you need tensors. LC -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: Questions about the Equivalence Principle (EP) and GR
On Sunday, February 24, 2019 at 6:41:00 AM UTC-7, Lawrence Crowell wrote: > > On Friday, February 22, 2019 at 4:40:31 PM UTC-6, agrays...@gmail.com > wrote: >> >> >> >> On Friday, February 22, 2019 at 1:34:31 PM UTC-7, Brent wrote: >>> >>> >>> >>> On 2/21/2019 10:47 PM, agrays...@gmail.com wrote: >>> >>> >>> *Even if gravitons are detected, and they account for "force" consistent >>> with the other three forces, wouldn't there remain the task of changing the >>> form of gravity to make it covariant? AG* >>> >>> >>> Gravitons, as quanta of the metric field, are already relativistic >>> particles and covariant. >>> >> >> *I thought it's the equations of motion for the particular force, not the >> mediating particles, that must be covariant. On a related topic for this >> thread, where does GR depart from Mach's principle? That is, what did >> Einstein implicitly (or explicitly) deny about Mach's principle? TIA, AG * >> >>> >>> *Would that require tensors? AG* >>> >>> > General relativity is covariant, and curvature is expressed according to > Riemann tensors. > > LC > *Thanks, but I think you missed the thrust of my question; namely, if a theory using gravitons is independent of GR, since it would have to be covariant, could that be done without tenors, or are tensors nevertheless necessary. AG* -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: Recommend this article, Even just for the Wheeler quote near the end
On Friday, February 22, 2019 at 3:18:01 PM UTC-6, Brent wrote:
>
>
>
> On 2/22/2019 11:39 AM, Lawrence Crowell wrote:
>
> This sounds almost tautological. I have not read Masanes' paper, but he
> seems to be saying the Born rule is a matter of pure logic. In some ways
> that is what Born said.
>
> The Born rule is not hard to understand. If you have a state space with
> vectors |u_i> then a quantum state can be written as sum_ic_i|u_i>. For an
> observable O with eigenvectors o_i the expectation values for that
> observable is
>
> sum_{ij} = sum_{ij} = sum_ip_io_i.
>
> So the expectations of each eigenvalue is multiple of the probability for
> the system to be found in that state. It is not hard to understand, but the
> problem is there is no general theorem and proof that the eigenvalues of an
> operator or observable are diagonal in the probabilities. In fact this has
> some subtle issues with degeneracies.
>
>
> Doesn't Gleason's theorem show that there is no other consistent way to
> assign probabilities to subspaces of a Hilbert space?
>
> Brent
>
It is close. Gleason's theorem tells us that probabilities are a
consequence of certain measurements. So for a basis Q = {q_n} then in a
span in Q = P{q_n}, for P a projection operator that a measure μ(Q} is
given by a trace over projection operators. This is close, but it does not
address the issue of eigenvalues of an operator or observable. Gleason
tried to make this work for operators, but was ultimately not able to.
Many years ago I had an idea that since the trace of a density matrix may
be thought of as constructed from projection operators with tr(ρ_n) = sum_n
|c_n|^2P_n, that observables that commute with the density matrix might
have a derived Born rule following Gleason. Further, maybe operators that
do not commute then have some dual property that still upholds Born rule. I
was not able to make this work.
LC
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to everything-list+unsubscr...@googlegroups.com.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
Re: Questions about the Equivalence Principle (EP) and GR
On Saturday, February 23, 2019 at 6:04:15 PM UTC-6, agrays...@gmail.com wrote: > > > > On Saturday, February 23, 2019 at 6:53:09 AM UTC-7, Philip Thrift wrote: >> >> >> >> On Saturday, February 23, 2019 at 7:25:21 AM UTC-6, John Clark wrote: >>> >>> On Fri, Feb 22, 2019 at 11:08 PM wrote: >>> >>> > *In GR, the paths are determined by geometry in the absence of forces, not by mediating particles.* >>> >>> >>> Yes, that's because General Relativity is a classical theory that is not >>> quantized, it has so far passed every experimental test posed to it with >>> flying colors but we know it can't be entirely correct because when we ask >>> it what happens when things become very small and very massive, such as in >>> the center of Black Holes, it gives the absurd answer of infinity. Neither >>> Quantum Mechanics or General Relativity works when things get massive and >>> small, perhaps quantizing General Relativity will fix this or maybe there >>> is some other way to do so. Nobody knows. >>> >>> > *I could be mistaken, but I see gravitons as being part of a distinct theory of gravity, which might give the same results as GR,* >>> >>> >>> Nobody has ever experimentally detected a graviton and it's extremely >>> unlikely anybody ever will, so if they make the same predictions as >>> standard General Relativity there would be no point in introducing the >>> idea. >>> >>> John K Clark >>> >>> >> >> If all experiments proposed to determine if gravity is quantized* fail* >> >> Such measurements, they say, could enable them to uncover the quantum >> nature of gravity and determine whether or not gravity is quantized. >> >> >> >> https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.122.071101 >> >> >> that is: the search for a quantized gravity is a wild goose chase >> >> what do theorists do then? >> >> (I asked Hossenfelder. No answer.) >> >> - pt >> > > *The article you cite indicates increasing hypothetical sensitivity for > measuring gravity for tiny effects. If gravity can be quantized, what > exactly would be quantized? Bruce says that gravity waves would involve > gravitons under a quantized theory. Is that all? AG * > I suppose it needs to defined *what an experiment would be* that would determine that gravity is quantized in a measurable way. Theories disconnected from experiments are mere math games. - pt -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: Questions about the Equivalence Principle (EP) and GR
On Friday, February 22, 2019 at 4:40:31 PM UTC-6, agrays...@gmail.com wrote: > > > > On Friday, February 22, 2019 at 1:34:31 PM UTC-7, Brent wrote: >> >> >> >> On 2/21/2019 10:47 PM, agrays...@gmail.com wrote: >> >> >>> >> *Even if gravitons are detected, and they account for "force" consistent >> with the other three forces, wouldn't there remain the task of changing the >> form of gravity to make it covariant? AG* >> >> >> Gravitons, as quanta of the metric field, are already relativistic >> particles and covariant. >> > > *I thought it's the equations of motion for the particular force, not the > mediating particles, that must be covariant. On a related topic for this > thread, where does GR depart from Mach's principle? That is, what did > Einstein implicitly (or explicitly) deny about Mach's principle? TIA, AG * > >> >> *Would that require tensors? AG* >> >> General relativity is covariant, and curvature is expressed according to Riemann tensors. LC -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
