On 5/26/2025 2:55 PM, Alan Grayson wrote:
On Monday, May 26, 2025 at 3:51:29 PM UTC-6 Alan Grayson wrote:
On Monday, May 26, 2025 at 5:57:36 AM UTC-6 John Clark wrote:
On Sun, May 25, 2025 at 3:33 PM Alan Grayson
<[email protected]> wrote:
/> I'm disagreeing with anyone, including you, who thinks
the EP is an absolute, when in fact it's a relative, an
approximation./
The Equivalence Principle, which is the foundation of General
Relativity, states that at sufficiently small scales there is
no way to tell the difference between a gravitational field
and a simple acceleration. And it is not an approximation. But
is it always correct? That is not certain because General
Relativity does not take Quantum Mechanics into account,
nevertheless so far at least the Equivalence Principle has
easily passed every experimental test put to it.
*Since the EP depends on measurement accuracy, it's
mischaracterized as some absolute principle. That's pretty obvious
regardless of contrary opinions, including Einstein's. AG *
*BTW, in what way is the EP the foundation of GR? Not at all obvious
how Einstein actually use the EP to develop GR. AG
*
Not a "foundation" just a suggestion that acceleration due to a
gravitational field could be modeled as force-free, geodesic motion in a
curved spacetime.
Brent
For fun I asked GPT to do "Deep Research" on the following
questions:
"Have there been any proposed experimental tests to see if
Einstein's Equivalence Principle remains true even when
quantum mechanics is taken into account? In other words tests
to determine if gravity can change the quantum entanglement of
two particles, and if not are any such tests planned?"
_SPOILER ALERT_: GPT's ultimate conclusion was "So far, all
completed tests have found *no anomalous effect* – entangled
states remain intact in different gravitational or accelerated
frames, consistent with EEP and standard quantum theory"
GPT put those words in boldface type, not me. Below is GPT's
full response:
========
Tests of the Equivalence Principle with Quantum Entanglement
Einstein’s equivalence principle (EEP) – that all objects fall
identically in a gravitational field – is classically tested
to extreme precision. Extending EEP to quantum systems,
especially entangled ones, poses conceptual challenges (the
EEP is classically formulated and its quantum generalization
“requires careful considerations”ar5iv.org
<https://ar5iv.org/pdf/2203.11628#:~:text=The%20EEP%20is%20however%20formulated,the%20notion%20of%20test%20particles>).
Recent proposals and experiments therefore ask: *Can gravity
alter quantum entanglement?* Would any change signal a
breakdown of EEP? Below we summarize key efforts, completed or
proposed, that probe this question using entangled photons or
atoms in varying gravitational or inertial conditions.
Space- and Satellite-Based Experiments
*
*Micius satellite test (Xu /et al./ 2019)* – An experiment
by Pan, Ren, Ralph /et al./ (China/U.S.) sent one photon
of a time-energy–entangled pair to orbit aboard the Micius
satellite while keeping the other photon on the
groundpub.math.leidenuniv.nl
<https://pub.math.leidenuniv.nl/~gillrd/Peking/Files/Xu-2019-Satellite-testing-of-a-gravitationa.pdf#:~:text=containing%20closed%20timelike%20curves%20and,the%20prediction%20of%20event%20formalism>.
This setup exposed the two photons to different
gravitational potentials. The goal was to test predictions
of a speculative “event formalism” model that entanglement
would *probabilistically decohere* when particles traverse
different gravity gradients. The result (published in
/Science/) was that no abnormal decoherence was seen: the
entanglement correlations matched standard quantum theory,
*not* the model’s decohering
predictionpub.math.leidenuniv.nl
<https://pub.math.leidenuniv.nl/~gillrd/Peking/Files/Xu-2019-Satellite-testing-of-a-gravitationa.pdf#:~:text=containing%20closed%20timelike%20curves%20and,the%20prediction%20of%20event%20formalism>.
In other words, despite the large gravitational potential
difference, the quantum entanglement survived intact.
/(Team: Jian-Wei Pan et al., USTC and collaborators;
status: completed 2017/19.)/
*
*Space-QUEST mission concept (Joshi /et al./ 2017)* – A
European “Quantum Entanglement Space Test” proposal
(ESA/Topical Team) led by Ursin, Ralph, Cacciapuoti /et
al./. This feasibility study outlined sending entangled
photon pairs between ground and the International Space
Station (ISS)ar5iv.labs.arxiv.org
<https://ar5iv.labs.arxiv.org/html/1703.08036v1#:~:text=Models%20of%20quantum%20systems%20on,theoretical%20predictions%20of%20Ralph%20and>.
One photon would be sent upward while its partner remained
on Earth, testing theories (e.g. by Ralph and co-workers)
that such a setup could *induce decoherence of
entanglement* if each photon samples a different
gravitational field gradientar5iv.labs.arxiv.org
<https://ar5iv.labs.arxiv.org/html/1703.08036v1#:~:text=Models%20of%20quantum%20systems%20on,theoretical%20predictions%20of%20Ralph%20and>.
The paper presents a detailed mission design (Space-QUEST)
and notes that under standard quantum field theory no
decoherence is expected, but some exotic models (the same
“event operator” models) predict irrecoverable loss of
entanglementar5iv.labs.arxiv.org
<https://ar5iv.labs.arxiv.org/html/1703.08036v1#:~:text=Models%20of%20quantum%20systems%20on,theoretical%20predictions%20of%20Ralph%20and>.
(Team: international quantum optics collaboration
including Austrian Academy of Sciences, University of
Vienna, ESA, etc.; status: proposed/concept study.)
Laboratory/Accelerated-Frame Experiments
*
*Acceleration (free-fall/centrifuge) test (Fink /et al./
2017)* – In Vienna, Fink, Ursin, Scheidl /et al./ placed a
polarization-entangled photon source and detectors on a
platform that was /dropped/ 12 m (microgravity) and
separately spun in a centrifuge up to 30 g. They measured
an entanglement witness for accelerations spanning 0.03 g
(near-free-fall) up to 30 gnature.com
<https://www.nature.com/articles/ncomms15304?error=cookies_not_supported&code=0de1ebbf-a81e-4d7e-a5a1-d5e23484627f#:~:text=at%20rest%20in%20gravitational%20fields%2C,uniform%20acceleration%20on%20photonic%20entanglement>.
The result (Nature Communications) was that entanglement
quality showed *no significant loss* beyond noise limits
at any acceleration testednature.com
<https://www.nature.com/articles/ncomms15304?error=cookies_not_supported&code=0de1ebbf-a81e-4d7e-a5a1-d5e23484627f#:~:text=at%20rest%20in%20gravitational%20fields%2C,uniform%20acceleration%20on%20photonic%20entanglement>.
In effect, even extreme inertial forces (equivalent to
gravitational fields by the EP) did not degrade the photon
entanglement. The experiment set an upper bound on any
acceleration-induced decoherence of the entangled
statenature.com
<https://www.nature.com/articles/ncomms15304?error=cookies_not_supported&code=0de1ebbf-a81e-4d7e-a5a1-d5e23484627f#:~:text=at%20rest%20in%20gravitational%20fields%2C,uniform%20acceleration%20on%20photonic%20entanglement>.
/(Affiliation: Vienna Institute of Quantum Optics (IQOQI)
and University of Vienna; status: completed 2017.)/
*
*Rotational (Sagnac interferometer) test (Cromb /et al./
2023)* – At the University of Glasgow, Cromb, Padgett,
Faccio /et al./ placed a Hong–Ou–Mandel interferometer
(entangled photons) on a rotating platform (fiber Sagnac
loop). They observed that as rotation rate increased, the
two-photon interference pattern *flipped* from the usual
HOM dip to a peakjournals.aps.org
<https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L022005#:~:text=a%20Hong,curved%20space%20on%20quantum%20entanglement>.
This indicates that noninertial (rotating) motion
fundamentally altered the symmetry of the entangled state.
While not directly a gravity test, this table-top
demonstration (Phys. Rev. Research 2023) shows that
entangled photons are sensitive to rotational
(relativistic) effects and “paves the way” to test
entanglement in curved spacetimejournals.aps.org
<https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L022005#:~:text=a%20Hong,curved%20space%20on%20quantum%20entanglement>.
/(Affiliation: University of Glasgow; status: completed
2023.)/
Proposed and Future Tests
*
*Entangled-atom interferometer (Geiger & Trupke 2018)* – A
theoretical proposal (Phys. Rev. Lett.) by Geiger (Paris
Observatory) and Trupke (Vienna) suggests using *two
entangled atoms of different species* in a differential
free-fall interferometer. Each atom (e.g. ^85Rb and ^87Rb)
forms its own atom interferometer; the two are prepared in
an entangled superposition via a heralded photon detection
at the input beam splitterhal.science
<https://hal.science/hal-01707541/document#:~:text=We%20propose%20an%20experiment%20to,the%20detection%20of%20a%20single>.
The interferometers then measure the differential
acceleration of the two species. Crucially, because the
atoms start entangled, this probes WEP in a regime where
“the two particles involved … are not classically
independent, but entangled”hal.science
<https://hal.science/hal-01707541/document#:~:text=We%20propose%20an%20experiment%20to,the%20detection%20of%20a%20single>.
Their proposed setup (high-finesse cavity, Raman
processes) predicts sensitivity to Eötvös parameter η
below 10^−7hal.science
<https://hal.science/hal-01707541/document#:~:text=two%20particles%20involved%20in%20the,E%C3%B6tv%C3%B6s%20parameter%20can%20be%20achieved>.
/(Institutions: LNE-SYRTE/Observatoire de Paris,
University of Vienna; status: proposed in PRL 2018.)/
*
*Entanglement-witness protocols (Bose /et al./ 2023)* –
Sougato Bose and collaborators (UCL, Groningen, Glasgow)
have introduced the idea of a “quantum equivalence
principle” test using entanglement. They propose creating
massive particles in large spatial superposition and using
an entanglement entropy witness to detect any WEP
violationar5iv.org
<https://ar5iv.org/pdf/2203.11628#:~:text=quantum%20entities,principle%20via%20witnessing%20quantum%20entanglement>.
In essence, both matter and the gravitational source are
treated as quantum; any difference between inertial and
gravitational masses in this fully quantum regime would
reveal itself through lack of entanglement. Their 2022/23
paper provides a protocol for such experiments and argues
it is “unique” for testing the weak equivalence principle
in the quantum domainar5iv.org
<https://ar5iv.org/pdf/2203.11628#:~:text=quantum%20entities,principle%20via%20witnessing%20quantum%20entanglement>.
/(This work is theoretical/preprint (Entropy 2023) but
outlines concrete tabletop schemes.)/
*
*SUPREME-QG space mission (Shahriar /et al./ 2023–25)* – A
NASA-funded concept (NIAC Phase I, 2025) led by Selim
Shahriar (Northwestern U.) envisions a spaceborne WEP test
using *macroscopic entangled atomic states*nasa.gov
<https://www.nasa.gov/directorates/stmd/niac/niac-studies/supreme-qg-space-borne-ultra-precise-measurement-of-the-equivalence-principle-signature-of-quantum-gravity/#:~:text=entanglement%20to%20test%20the%20EP,N%20SC%20states%20are%20difficult>.
The idea is two simultaneous atom interferometers with
^85Rb and ^87Rb, each using a Schrödinger-cat–like state
of N≈10^6 entangled atoms generated by cavity
spin-squeezingnasa.gov
<https://www.nasa.gov/directorates/stmd/niac/niac-studies/supreme-qg-space-borne-ultra-precise-measurement-of-the-equivalence-principle-signature-of-quantum-gravity/#:~:text=entanglement%20to%20test%20the%20EP,N%20SC%20states%20are%20difficult>.
Such a many-particle entangled state behaves as one
massive superposition, boosting sensitivity by √N∼10^3.
The goal is to measure differential free-fall with
precision η∼10^−20nasa.gov
<https://www.nasa.gov/directorates/stmd/niac/niac-studies/supreme-qg-space-borne-ultra-precise-measurement-of-the-equivalence-principle-signature-of-quantum-gravity/#:~:text=entanglement%20to%20test%20the%20EP,N%20SC%20states%20are%20difficult>
– orders of magnitude beyond current tests. (The proposal
outlines technology development for these giant entangled
statesnasa.gov
<https://www.nasa.gov/directorates/stmd/niac/niac-studies/supreme-qg-space-borne-ultra-precise-measurement-of-the-equivalence-principle-signature-of-quantum-gravity/#:~:text=entanglement%20to%20test%20the%20EP,N%20SC%20states%20are%20difficult>.
Status: concept study, NIAC-awarded 2025.)
Each of these efforts is explicitly aimed at the *intersection
of gravity and entanglement*. So far, all completed tests have
*found no anomalous effect* – entangled states remain intact
in different gravitational or accelerated frames, consistent
with EEP and standard quantum theorypub.math.leidenuniv.nl
<https://pub.math.leidenuniv.nl/~gillrd/Peking/Files/Xu-2019-Satellite-testing-of-a-gravitationa.pdf#:~:text=containing%20closed%20timelike%20curves%20and,the%20prediction%20of%20event%20formalism>nature.com
<https://www.nature.com/articles/ncomms15304?error=cookies_not_supported&code=0de1ebbf-a81e-4d7e-a5a1-d5e23484627f#:~:text=at%20rest%20in%20gravitational%20fields%2C,uniform%20acceleration%20on%20photonic%20entanglement>.
Future and proposed experiments (e.g. entangled atoms in
free-fall) aim to push these tests into new regimes; any
observed entanglement degradation tied to gravity would signal
new physics.
*Sources:* Peer-reviewed articles and official reports as
cited abovepub.math.leidenuniv.nl
<https://pub.math.leidenuniv.nl/~gillrd/Peking/Files/Xu-2019-Satellite-testing-of-a-gravitationa.pdf#:~:text=containing%20closed%20timelike%20curves%20and,the%20prediction%20of%20event%20formalism>
--
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 [email protected].
To view this discussion visit
https://groups.google.com/d/msgid/everything-list/34c2f86b-10f0-456b-92ea-24042e1a7f46n%40googlegroups.com
<https://groups.google.com/d/msgid/everything-list/34c2f86b-10f0-456b-92ea-24042e1a7f46n%40googlegroups.com?utm_medium=email&utm_source=footer>.
--
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 [email protected].
To view this discussion visit
https://groups.google.com/d/msgid/everything-list/a40c5615-6bf6-4192-a8ac-17332bb4f51b%40gmail.com.
