
Gravity: We might have been getting it wrong - ryan_j_naughton
https://phys.org/news/2020-01-gravity-wrong.html
======
scrumper
Agh, mildly infuriating (enfrustrating?) article. A little tease about the
result and then several paragraphs about how science is serendipitous and face
to face interactions are better than email and video conferencing.

~~~
pdonis
_> mildly infuriating (enfrustrating?) article_

Par for the course for phys.org.

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rubyn00bie
Because like every article I tried to find was pretty much the exact same
rubbish overview, here's a link to the pre-print paper:
[https://arxiv.org/pdf/1810.05337.pdf](https://arxiv.org/pdf/1810.05337.pdf)

As someone very not versed in physics, the paper is actually... really
readable so far and short (I'm almost done). At the very least, there is more
information than anything mentioned in the links/summaries I could find.

~~~
s1dev
The real paper is
[https://arxiv.org/pdf/1810.05338.pdf](https://arxiv.org/pdf/1810.05338.pdf)

1810.05337 is a summary of results for PRL

Both are very good

~~~
JadeNB
Eternal plea: for those of us who want to see what the paper's about before
downloading it, it's better to link to the abstract at
[http://arxiv.org/abs/1810.05338](http://arxiv.org/abs/1810.05338) .

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tiborsaas
Even the title is wrong, we know for a fact that we are getting gravity wrong.

A better article with actual content:

[https://www.ipmu.jp/en/20190619-symmetry](https://www.ipmu.jp/en/20190619-symmetry)

~~~
pdonis
_> we know for a fact that we are getting gravity wrong_

This statement is way, way too strong. We have a theory of gravity, General
Relativity, which has had its predictions confirmed by countless experiments,
in some cases to thirteen or fourteen decimal places. That is not "getting it
wrong".

Many physicists believe that GR, as well confirmed as it is, can't be the
final fundamental theory of gravity because it's not a quantum theory. But
nobody has yet found a quantum theory of gravity that (a) is consistent with
the rest of quantum mechanics, and (b) makes experimental predictions that
have been confirmed. Unless and until both (a) and (b) are done, the claim
that we are "getting it wrong", even in the restricted sense of not having a
final fundamental theory of gravity, because GR isn't a quantum theory is just
speculation and might itself be wrong. It should certainly not be stated with
the confidence you are stating it.

~~~
thaumasiotes
> Many physicists believe that GR, as well confirmed as it is, can't be the
> final fundamental theory of gravity because it's not a quantum theory. But
> nobody has yet found a quantum theory of gravity that (a) is consistent with
> the rest of quantum mechanics

It was my (lay) impression that we believe general relativity cannot be the
final fundemental theory of gravity because general relativity itself is not
consistent with quantum mechanics. Whether general relativity is a quantum
theory or not is beside the point; we want to have a theory -- any theory --
that is consistent with itself. Right now we have two separate theories
(general relativity / quantum mechanics) that can't be combined because they
conflict with each other.

Obviously, that in itself doesn't prove that the problem is in the theory of
gravity, but it does prove the problem is either in the theory of gravity or
the theory of quantum mechanics, and we have to be getting one of them wrong.

~~~
ncmncm
> _the problem is either in the theory of gravity or the theory of quantum
> mechanics, and we have to be getting one of them wrong._

Not true: we could also be getting them both wrong.

~~~
thaumasiotes
There is no way to be getting both of them wrong but not be getting one of
them wrong.

~~~
syockit
Pedantically that is true, but you should still word it as "at least one of
them" to avoid being misunderstood.

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wrycoder
Much more information from a previous phys.org:

[https://phys.org/news/2019-05-constraints-symmetries-
hologra...](https://phys.org/news/2019-05-constraints-symmetries-
holography.html)

Their work assumes the AdS/CFT correspondence.

"Our new paper provides a rigorous proof of this claim in the context of the
AdS/CFT correspondence, where quantum gravity is defined in a mathematically
precise way, and we have done so in the most general way, excluding all
possible global symmetries from quantum gravity,"

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reggieband
Interesting ... another time holography in the context of physics has come up.
Youtube recommended the Wired series where some expert explains some concept
at different levels and one recent one was on Gravity [1]. In the expert
section they talk briefly about holography and how a two dimensional surface
seems to be able to encode all of the information of a three dimensional
volume. They go on to speculate how this might relate to the event horizon of
black holes. I get a bit lost since it is heavily edited and they are clearly
talking about things beyond my ken. My takeaway was that there is a
possibility the information we thought was getting lost within blackholes is
actually still present within the surface of the event horizon.

There was also a brief mention of holography in this interview with String
Theorist Jim Gates on Lex Fridman's Youtube channel [2]. I can't remember the
exact context of how holography is related to strings but I believe he was
talking about how it could impact some of the maths behind the multiple
dimensions some string theories required.

[1] [https://www.youtube.com/watch?v=QcUey-
DVYjk](https://www.youtube.com/watch?v=QcUey-DVYjk)

[2]
[https://www.youtube.com/watch?v=vGQ3q4dO_9s](https://www.youtube.com/watch?v=vGQ3q4dO_9s)

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paulpauper
this article is way to vague. Do they means symmetry as it relates to string
theory or some other theory for quantum gravity? I was hoping for more info.

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ksaj
Modeling, even if incorrect, is important for at least 2 reasons. The most
obvious one is that we can refine the theory as new results come out of the
experiments. The second is that a successful model, even if wrong for the
experiment it was devised, will eventually shed light on a similar problem
elsewhere.

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rehasu
If you talk to physicists and they tell you we've got something right, stop
talking to them.

Every good(!) one knows that we got it wrong. Just a little less wrong than in
the previous model. You cannot get it right. It wouldn't be a model but
reality as a whole if you got it right. So the only questions are how you can
get it less wrong than the last model, and which of the available models is
most useful for the problem you are currently tackling. So yes, sometimes you
even want to use a more-wrong model because it fits your problem better.

edit: thought about bringing in an example, but honestly it would need too
much googling to be precise enough.

~~~
edem
> sometimes you even want to use a more-wrong model because it fits your
> problem better.

Or they are equal in fit, but the more wrong is easier to use.

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greesil
This part is fun: "Their result has several important consequences. In
particular, it predicts that the protons are unstable against decaying into
other elementary particles, and that magnetic monopoles exist."

~~~
alextingle
That caught my eye too. Magnetic monopoles would be very useful, if we could
find them.

~~~
greesil
What would you do with a magnetic monopole? I might make this an interview
question at work. Hmmm

~~~
hnuser123456
Make an infinite energy machine by having magnets on a rotor, surrounded by
monopoles on a stator (or vice versa), so the rotor is infinitely accelerated
with no external input energy. Hook it up to an alternator and harness the
free power.

~~~
jcranmer
I'm pretty sure that doesn't work for the same reason that replacing monopoles
with charged objects (which we can actually build!) doesn't produce a
perpetual motion machine.

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mindcrime
Huh, interesting. We know there are (or were) some fundamental asymmetries in
the universe, leading to, for example, the imbalance in matter vs anti-matter.
I wonder if this research will lead to anything in terms of understanding why
these kinds of asymmetries exist?

~~~
Ididntdothis
An interesting question is also why the universe has any kind of structure and
is not uniform.

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foxes
See [0] for the actual paper mentioned in the article.

[0] [https://arxiv.org/abs/1810.05338](https://arxiv.org/abs/1810.05338)

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tus88
Huh. We said the same thing a bit over a century ago.

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xhkkffbf
If we can't figure out gravity, what hope have we of doing ANY science? I mean
stuff falls. Everything falls. The orbits of the planets aren't that complex,
but gravity pretty much predicts them close to perfectly.

~~~
xenocyon
It's not that we can't model gravity at planetary-orbit scales; that's been
done. The issue is that relativity (which addresses gravity) is a good model
at large scales and the quantum "Standard Model" (which addresses the other
three forces) is a good model at small scales, but these two models are
incompatible with each other and no falsifiable theory that works at all
scales has yet been found.

~~~
Koshkin
They cannot be "incompatible with each other," otherwise Nature would be
"incompatible" with itself.

~~~
tsimionescu
The _models_ are incompatible with each other, which means that one or both
are somehow wrong, or there is some boundary we can't fathom between the small
scale and the large.

~~~
Koshkin
Wrong - we do know that the models are _not_ incompatible. (There exists a
_consistent_ mathematical framework that includes both.) Me, I was referring
to a simpler fact that these models are both _pretty damn close_ to what
Nature itself tells us.

