
Troubled Times for Alternatives to Einstein’s Theory of Gravity - allenleein
https://www.quantamagazine.org/troubled-times-for-alternatives-to-einsteins-theory-of-gravity-20180430/
======
daxfohl
I still think the answer will have to confront the problem of local realism.
It was the issue that drove Newton nuts (that gravitation was, in Einstein's
language "spooky action at a distance"), and Einstein resolved that through
Relativity, which redefined how we think about "distance". Now the lack of
local realism in QM is driving Einstein's ghost nuts. I think the resolution
of all this will _again_ redefine "distance" to take resolutions involving
quantum entanglement into account. Vaguely I picture some quantum relativity
theory where from the perspective of an entangled particle it's still d=0 from
its entangled partner and _everything else_ is splitting apart. So like
relativity, it's all about which perspective you take. Then perhaps with these
relative distances, and however the math falls out with some kind of quantum
Lorentz transforms _maybe_ we see that in galaxies with lots of entangled
particles this can slow down rotation.

That said, dark matter is entirely possible too. There's no particular reason
to think that all particles need to have an EM effect as well. In fact it's
somewhat crazy to think they _should_. Why _wouldn 't_ there be particles that
only show themselves gravitationally? Or through other perhaps insanely strong
forces that for whatever evolutionary reason Earth Life is just not evolved to
care about or see even indirectly.

 _That_ said, I have no training in physics and this is entirely crackpot
concept. (Of
[http://www.goodtheorist.science/](http://www.goodtheorist.science/) I've only
read ~6.)

~~~
cobbzilla
Your idea reminds me of Wheeler's "single electron universe" [1]. I think
you're on to something but I also think the next big step will involve a
formal (re)definition of time as well as distance.

[1] [https://en.wikipedia.org/wiki/One-
electron_universe](https://en.wikipedia.org/wiki/One-electron_universe)

~~~
dbasedweeb
When you think about particles as excitations of a field, the
indistinguishable nature of said particles stops being such a puzzle.

~~~
daxfohl
But the concept of a field itself was troubling to 18-19th century physicists.
"So you put this (mass/charge/entanglement/whatever) here and automagically
there's this whole force that extends across the universe in zero time? How?
Why?"

Philosophically I don't know if this question has ever been answered
satisfactorily. But over the last 100 years fields have become so
mathematically convenient that they're too hard _not_ to use.

~~~
dbasedweeb
Well those 18th-19th century anything didn’t have a concept of entanglement or
FTL, they were struggling with the notion that light, gravity, and other
forces could propagate without a medium. They saw that waves could be
transmitted through water, sound through air, and the idea that light or
gravity could be transmitted through vacuum was baffling. Their resolution to
the issue was to propose the existence of a substance which was invisible,
intangible, but which permeated everything: the luminiferous ether. Light, in
their understanding, wasn’t really moving through a vacuum, but this ever-
present “stuff” instead. That started to fall out of favor long after the 18th
century, and was finally conclusively shot down by Michelson and Morley with
their interferometry.

The problem Einstein and others grappled with was different, and concerned the
fact that according to relativity nothing should exceed c. Entangled particles
seemed to violate that principle, because the collapse to a given pair of
states was instantaneous. The modern resolution to that is more practical than
philosophical, and points out that _information_ isn’t transmitted faster than
light in entangled particles. Information propagates at or below c, even
though at some scale entangled particles are statistically correlated.
Relativity is only violated, and causality threatened if information is
transmitted FTL, but entanglement doesn’t allow for that. You need a classical
channel make entanglement work for communication, and that classical channel
is going to be no faster than light. Without a classical channel, entanglement
just gives you random noise.

~~~
goatlover
> Relativity is only violated, and causality threatened if information is
> transmitted FTL, but entanglement doesn’t allow for that. You need a
> classical channel make entanglement work for communication, and that
> classical channel is going to be no faster than light. Without a classical
> channel, entanglement just gives you random noise.

But none of that answers the 18th-19th century Physicists question about how
fields extend across the universe, or how light propagates in empty space.
What the hell is a field anyway?

Also, it doesn't explain how the expansion of space happens, what made
inflation happen, and what dark energy is.

~~~
dbasedweeb
A very smart guy named Alfred Korzybski said, “The map is not the territory.”
It’s important to not get too hung up on epistemological implications of our
models of reality, because they are just models. On a practical level a field
is something which has a value at every point, that value can be a scalar,
vector, or tensor depending on the nature of the field. For some good
discussion I think this could help:
[https://physics.stackexchange.com/questions/13157/what-
is-a-...](https://physics.stackexchange.com/questions/13157/what-is-a-field-
really)

 _Now, it is very easy to get hung up on this "Is it real or not" thing, and
most people do for at least a while, but please just put it aside. When you
peer really hard into the depth of the theory, it turns out that it is hard to
say for sure that stuff is "stuff". It is tempting to suggest that having a
non-zero value of mass defines "stuffness", but then how do you deal with the
photo-electric effect (which makes a pretty good argument that light comes in
packets that have enough "stuffness" to bounce electrons around)? All the
properties that you associate with stuff are actually explainable in terms of
electro-magnetic fields and mass (which in GR is described by a component of a
tensor field!). And round and round we go._

Light doesn’t propagate in empty space, because space isn’t empty, it’s
permeated with quantum fields in constant flux. What light doesn’t require is
a medium, and a field is not a medium. The problem here is that these theories
are really described in terms of a bunch of math, and when we use words to
describe those theories, something is lost in translation. There are no words
that fully capture what a field is in QFT, you must use math.

Once you adopt that perspective, inflation would just be the result of another
field with particular properties (esp. a given range of potential energy
curves). Of course, inflation is an untested theory, and there are competing
ones which try to explain the apparent homogeneity and isotropy of the
universe. Inflation is probably the most popular, but it doesn’t rest on the
kind of firm foundation that QED does.

------
Zamicol
My money is still on additions/modifications to relativity in the next 100
years. (Sorry for the sources, just using Google to pull up something.)

\- Hubble's constant has not been calculated, and when it is, there are
problems. [https://www.space.com/38496-hunt-for-hubble-constant-
standar...](https://www.space.com/38496-hunt-for-hubble-constant-standard-
model.html)

\- Like the fallacious search for Vulcan, there are modern problems with the
orbits of some of the outer planets.
[https://solarsystem.nasa.gov/planets/hypothetical-
planet-x/i...](https://solarsystem.nasa.gov/planets/hypothetical-planet-x/in-
depth/)

\- A galaxy with 99 percent dark matter and one almost without any.
[https://www.quantamagazine.org/a-victory-for-dark-matter-
in-...](https://www.quantamagazine.org/a-victory-for-dark-matter-in-a-galaxy-
without-any-20180328/) [https://www.theverge.com/2016/8/25/12647540/dragonfly-
galaxy...](https://www.theverge.com/2016/8/25/12647540/dragonfly-galaxy-
discovered-99-9-percent-dark-matter-stars)

\- The bullet cluster, the speed of rotation in galactic arms, etc.

\- The apparent changing rate of expansion in the universe.

\- We have no idea of the physics behind red shift "caused by the metric
expansion of space".

\- We still don't know what gravity actually is.

The 1998 discovery of the accelerating expansion of the universe was
beautifully simple and clean. It proved a huge swath of experts dead wrong.
[https://en.wikipedia.org/wiki/2011_Nobel_Prize_in_Physics](https://en.wikipedia.org/wiki/2011_Nobel_Prize_in_Physics)

Dark matter/energy could be apart of the mix, but in light of the problems I
would not bet it's the end of the story.

~~~
sxcurry
Your second point - I don't think the potential Planet Nine has anything to do
with "problem with the orbits of some of the outer planets". It has been
proposed as a solution to the orbits of some distant smaller Kuiper Belt
objects. This in return doesn't really have anything to do with relativity,
just basic orbital mechanics.

~~~
Zamicol
I could have sworn there were problems with Pluto's orbit where it was
faster/slower than it should have been, but it looks like I'm wrong.

>Specifically, this paper shows that, contrary to recent assertions in the
literature, the current ephemeris for Pluto does not preclude the existence of
the Pioneer effect. We show that the orbit of Pluto is currently not well
enough characterized to make such an assertion.

[https://arxiv.org/pdf/0905.0030.pdf](https://arxiv.org/pdf/0905.0030.pdf)

~~~
bsder
The Pioneer Effect has been explained as "anisotropic radiation pressure
caused by the spacecraft's heat loss".

[https://en.wikipedia.org/wiki/Pioneer_anomaly](https://en.wikipedia.org/wiki/Pioneer_anomaly)

~~~
nonbel
That's an interesting case because they "solved" the problem by basically
increasing the estimated uncertainty. See the dual sets of error bars in Fig
3: [https://arxiv.org/abs/1204.2507](https://arxiv.org/abs/1204.2507)

------
mirimir
> Theorists have dozens of alternative gravity theories that could potentially
> explain dark matter and dark energy, Freire said. Some of these theories
> can’t make testable predictions, Archibald said, and many “have a parameter,
> a ‘knob’ you can turn to make them pass any test you like,” she said. But at
> some point, said Nicolas Yunes, a physicist at Montana State University,
> “this gets silly and Occam’s razor wins.”

That's very kind. Some would say that theories that can't make testable
predictions, or are highly tunable, just aren't science.

~~~
cryptonector
Right now that includes Dark Matter...

~~~
mirimir
Well, it's always seemed _ad hoc_ to me.

But then, IANAP so hey.

------
Xeoncross
The article shows two demonstrations: 1) a spiral galaxy and 2) a triple
system (a neutron star and a white dwarf orbit each other, with another white
dwarf orbiting the pair at a distance).

I think the spiral galaxy is showing that the problem is that it still has the
arms attached. After this amount of time they should not be there so either
the amount of time assumed is wrong or something is modifying the speed (like
dark energy, modified Newtonian dynamics, etc).

However, I don't understand what the "fall" in the triple system is about.
What are they measuring that agrees with Newtonian Physics?

~~~
cryptonector
Are we reading the same FA? The one I read was about a neutron star
collision/merger, and a triple star system with a pulsar, and also a double-
pulsar system. The word 'spiral' does not appear.

------
aleksei
To anyone reading the comments, don't bother.

------
ksaxena
This article discusses LIGO's detection of gravitational waves as a problem
for alternate theories of gravity. But the claim of that discovery seems to
have been withdrawn by the LIGO team. Here:
[https://www.nature.com/news/gravitational-waves-discovery-
no...](https://www.nature.com/news/gravitational-waves-discovery-now-
officially-dead-1.16830)

I'm an amateur but something feels amiss to me here. Can anyone shed more
light on this contradiction?

~~~
civilitty
That article is about a redaction from the research team at BICEP2, a
telescope in the South Pole. It has nothing to do with the Super LIGO
detector, which has detected gravitational waves from black hole collisions
several times now.

~~~
pdkl95
LIGO's comments[1] about the 6 gravitational wave detections they are
currently confirming (and related publications):

[1] [https://www.ligo.org/detections.php](https://www.ligo.org/detections.php)

After following the major science experiments over the last ~15 years, I've
gotten the impression that the LIGO team is being _very_ careful to not
announce anything prematurely.

In an interview[2] with Prof. Rana Adhikari about the first detection, he
describes how incredibly lucky it was to detect a very strong wave in the
middle of the detector's sensitivity range, only _~30 minutes_ after each site
independently enabled data collection. That's the type of situation that
raises serious questions about the validity of the data and might even suggest
sabotage (someone could be faking data). Fortunately, it sounds like they were
careful to investigate the alternative explanations, including searching the
labs for anything that looked like a possible sabotage device. It's always
good to see scientists paying extra attention to rigor.

[2]
[https://www.youtube.com/watch?v=ViMnGgn87dg](https://www.youtube.com/watch?v=ViMnGgn87dg)

~~~
nonbel
Wow, I just read about the latest gravitational wave and I see that _once
again_ they detected it by deviating from the procedure used to generate the
background model:

>"Although such times are in general not included in searches, it was
determined that LHO strain data were una ffected by the procedure at
frequencies above 30 Hz, and may thus be used to identify a GW source and
measure its properties."
[https://www.ligo.org/detections/GW170608/paper/GW170608_subm...](https://www.ligo.org/detections/GW170608/paper/GW170608_submitted.pdf)

I'm not saying they aren't seeing anything, but the false alarm rate
calculations are meaningless unless they process the data the exact same way
for background. They keep making these special exceptions every time.

EDIT:

Mostly just saving this for myself...

Here it is for the 5th detection:

>"Single-detector gravitational-wave triggers had never been disseminated
before in low latency. Given the temporal coincidence with the Fermi-GBM GRB,
however, a GCN Circular was issued at 13:21:42 UTC (LIGO Scientific
Collaboration & Virgo Collaboration et al. 2017a) reporting that a highly
significant candidate event consistent with a BNS coalescence was associated
with the time of the GRB."

[http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9](http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9)

4th detection:

This one looks clean (but for the 1st detection the questionable info was not
included in the main paper).

[https://www.ligo.org/detections/GW170814/paper/GW170814-PRLp...](https://www.ligo.org/detections/GW170814/paper/GW170814-PRLpublished.pdf)

2nd detection:

>"Since GW150914 had already been confirmed as a real gravitational-wave
signal [4], it was removed from the data when estimating the noise
background."

[http://link.aps.org/doi/10.1103/PhysRevLett.116.241103](http://link.aps.org/doi/10.1103/PhysRevLett.116.241103)

Earlier discussion about 1st and 3rd detections:

Its claimed "significance estimates come solely from the offline analysis",
which seemed to satisfy me at the time...
[https://news.ycombinator.com/item?id=14462719](https://news.ycombinator.com/item?id=14462719)

------
d_burfoot
I've been thinking recently that physics should import an idea from software
engineering: the test harness. For physics, the test harness would include a
large database of X/Y pairs where X represents an experimental configuration
and Y represents the outcome.

Theories of physics would be instantiated as software libraries. The most
modern physics library would pass the vast majority of the tests, by correctly
predicting the outcome Y for every configuration X. But since physics is not
yet complete, there would presumably be some tests that the best current
theories cannot pass, or can only pass by jumping through some really ugly
hoops - such as postulating the existence of dark matter and energy.

To be taken seriously when proposing a new theory, a researcher must submit an
update to the current library, and show that the new theory passes all the
tests. The research can also identify new X/Y combinations, not covered in the
current test suite, where the new theory diverges from the old one.
Experimentalists could then decide the question by running the corresponding
experiments and adding the results to the main suite.

~~~
dbasedweeb
This is already essentially how it works. A new theory has to be complementary
to old ones. This is often said in terms of “matching the predictions of...”
another theory. There are more standards of course, but that’s the baseline. A
lot of pet theories people have for things like QM fall apart because they
don’t match the tested predictions of QM. For example, Special and General
Relativity make new and more accurate predictions which complement, but do not
contradict Newtonian theory.

An issue with a theory replacing QM for example, other than the high degree of
precision needed, is Bell’s Theorem, which tends to rule out LHV theories.
[https://en.m.wikipedia.org/wiki/Bell%27s_theorem](https://en.m.wikipedia.org/wiki/Bell%27s_theorem)

