
Is gravity not actually a force? Forcing theory to meet experiments - lotusleaf1987
http://arstechnica.com/science/news/2011/04/is-gravity-a-result-of-thermodynamics.ars
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haberman
I really don't understand the question "is gravity a force?" It reminds me of
the Feynman story:

    
    
        > "Say, Pop, I noticed something. When I pull the wagon,
        > the ball rolls to the back of the wagon. And when I'm 
        > pulling it along and I suddenly stop, the ball rolls
        > to the front of the wagon. Why is that?
        >
        > "That, nobody knows," he said. "The general principle is 
        > that things which are moving tend to keep on moving, and 
        > things which are standing still tend to stand still, unless 
        > you push them hard. This tendency is called 'inertia,' but 
        > nobody knows why it's true." Now, that's a deep 
        > understanding. He didn't just give me the name.
    

I don't get why this is "a deep understanding." Why should someone have to
have some deep reason for believing that something at rest won't spontaneously
begin moving? Should you also need a profound explanation for why things don't
spontaneously change their mass or sprout kangaroo legs and start singing "La
Bamba?"

And what does it mean to ask if "gravity" is not actually a "force?" The idea
of a "force" is just an abstraction we use to describe our observations. How
is it a deep question to ask whether we give gravity the label of "force" or
not?

~~~
maggit
> I really don't understand the question "is gravity a force?"

The question is not "is gravity a force?". The question is "What is gravity?"

An accepted answer, what I was taught in school, and what I would answer if
you asked me is "it's a force". And labeling something as "a force" has huge
implications for people that know what that label means.

If a four year old asked me "What is gravity?", I'd know better than to give
him a label, because he wouldn't know what a force is from school. Obviously.

If it turns out gravity is not really a force -- if modelling gravity as a
force breaks down at some point -- that's a good fundamental result. It is a
falsification of the theory "Gravity is a force". (So the line of thought
goes: "What is gravity?", "It is a force!", "Is gravity really a force?",
"Perhaps not!")

How is this not helping us attaining a deep understanding? How is this not
advancing science? How is this any different from any science?

~~~
mryall
> If it turns out gravity is not really a force ...

It definitely isn't. The word "force" implies a Newtonian model for physics.
Under general relativity, gravity isn't seen as a force but a consequence of
curved space-time.

The title was probably chosen by an editor without deep knowledge of the
subject. It doesn't accurately describe the article's content either.

~~~
maggit
I humbly bow to anybody's superior knowledge of physics.

To clarify, I wasn't actually trying to say anything about physics, just about
science. So it would have been better phrased as a hypothetical; If we assume
that gravity is currently best modeled as a force, why is it valuable (nay,
essential) to question whether or not it actually is a force? I hope I
answered that hypothetical properly :)

------
fleitz
I thought Einstein said that over 100 years ago. From my understanding gravity
is not a force but a curvature of space time, did I misread something?

The really interesting bit about black holes and universes encoding
information on the surface is this: The Chandrasekhar limit radius for a mass
equal to the weight of the universe, once you figure that out, look up the
best known estimate for the radius of the universe.

~~~
Stormbringer
Or in other words, a black hole is something that light never escapes from,
and the universe is also something that light never escapes from.

Ignoring hawking radiation of course...

... unless the cosmic microwave background is the equivalent of the hawking
radiation given off by black holes (note: for the picky, before you object,
consider that hawking radiation consists of when one part of a short lived
mutually annihilating pair of particles falls into the event horizon and the
other falls out (hence gets radiated away) and thus from the point of view of
those inside the black hole it would appear as those there was a constant rain
of particles falling in... which I'm equating here to the microwave background
noise), which would imply that our universe is shrinking...

...unless it implies that our universe is getting bigger, maybe if our
universe is a black hole with hawking 'radiation' then on the other side of
the 'universal event horizon' things work a bit differently and it is matter
which is more likely to fall in, not anti-matter...

... which would explain why baryonic matter in this universe has an
overwhelming tendency towards matter instead of anti-matter, which is one of
those really big still outstanding questions in science...

~~~
cmaggard
Did you read this somewhere or are these your own thoughts? I'd like a
citation or to subscribe to your newsletter, respectively. Very intriguing.

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PaulHoule
What's remarkable about this is that it uses the one winning strategy we've
got in quantum gravity today.

In QG we've got two things: (i) general principle such as unitarity and the
holographic principle, and (ii) specific models such as loop quantum gravity,
string theory models, supergravity, etc.

Results based on type (ii) information are always going to be iffy because the
detailed models are all about what happens on the Planck scale or inside a
black hole so experimental confirmation is going to be difficult -- it may be
hard or impossible to prove or disprove any one of these models.

Type (i) results, however, will hold no matter what is correct on the type
(ii) level. Because we're not assuming a huge amount of "superstructure", the
results are much more intellectually convincing than type (ii) results -- and
with more certainty on the theoretical front, there's more "gravity" in the
confrontation of theory and experiment...

(We accomplish very little by experimentally disproving any particular type
(ii) model because we've got 100 others to take its place)

~~~
Jach
Your last bit reminded me of something one of my professors said. I remember
it as "Hmm, our theory didn't pan out at the predicted 7 TeV? Must be at 14."

------
mrcodydaniel
Redefining the laws of physics in terms of information theory is not new, but
so far as I know hasn't been tried and expressed well with gravity.

Certainly all of QM can be done in terms of information, and I think Seth
Lloyd is working on this right now. Cool to see a new take on gravity though.

Also, it's neat to think that black holes are deterministic from their
surface, though it's sort of required if you force thermo on it. After all, if
the information's beyond the event horizon, it's not really in our universe,
and thus violates thermo assumptions about closed systems. Sort of a case of
mashing theory against the universe.

-Cd

~~~
long
This same guy that the article discusses, Erik Verlinde, has formulated a
"holographic" theory of gravity, which made some waves about a year ago.

~~~
jarin
I hope that pun was intentional

------
SeanLuke
> it has not gone through peer review

I think this is really all we need to know.

~~~
JonnieCache
It has not _yet_ gone through peer review. It's a long process. I doubt that
this is one those "scientists" who deliberately avoid peer review.

Ars regularly do this, discuss papers that are "hot off the press" and have
not been fully peer reviewed yet. This is simply the reality of following the
bleeding edge of science. They are always up front about it, I don't see a
problem.

~~~
SeanLuke
The problem I have with this, as a reviewer, is that an amazing amount of junk
gets submitted to journals with no hope of passing peer review. With your
standard, all this junk is merely things "hot off the press". As to whether
this is "one of those scientists", I don't know (probably not). But the
article hints that his idea has _already_ been falsified, and yet it still
goes through with publishing about it breathlessly!

Peer review is a more important standard than you take it to be. For every
announced-but-not-yet-peer-reviewed revolutionary discovery -- Wiles's proof
of Fermat's Last Theorem comes to mind -- there are a _massive_ number of
P!=NP papers "awaiting peer review", every one of which is dead wrong, but
each of which will excite some moron in the press to write about it.

The press has such an incredibly bad track record at this that my personal
estimate, based on the performance of similar breathless "hot off the presses"
articles I have read, is that without reading the article there is over a 95%
probability that this paper won't pass peer review. Once I _read_ the article,
based on the fact that half of it is a sheepish admission that there are
problems with the theorem, I think that this prior probability was more than
confirmed.

With a probability this low, I see no reason to waste my time reading
breathless articles like this.

~~~
scott_s
I don't think you're giving enough credit to the author of this summary by
calling it "breathless." His conclusion is:

 _This is how science works. Ideas are proposed, they are backed up, they are
shot down. Over time, it would not surprise me to see Verlinde defend his
work. Perhaps Kobakhidze's derivation and its extension to the microscopic
case is incorrect. Perhaps Verlinde will revisit his original work to revise
how microscopic cases should be handled. Whatever happens, science will move
on; time, further arguments, and experiments will be the ultimate arbiter of
which drastically different view of reality is correct._

I think this article has two purposes: explain a new, untested theory, and
demonstrate how science works in practice. He links to, and discusses, two
papers that refute the theory. You call that a "sheepish admission," but I
think that was one of his goals.

~~~
JonnieCache
Ars deal with this in the _first paragraph:_

 _"In this article, we are going to look at a manuscript that purports to
overturn hundreds of years of accepted ideas about gravity, and use it as an
illustration of how controversial ideas are dealt with in modern physics."_

I don't think you can be any more up front than that. It's not a sheepish
admission, it's the whole point of the article. Ars are trying to highlight
exactly the problems you're talking about.

------
Tycho
Could light be like a harmonic overtone of gravity at a much higher frequency,
with both being vibrations/ waves in the ether of space-time?

/serious-face

------
zeynel1
Gravity is not a force; gravity is a hoax. I am glad that physics
establishment finally is realizing this:
<http://science1.wordpress.com/2008/12/25/dear-physicist/>

~~~
teraflop
That's certainly an unorthodox view. As far as I can make out from that post
and the rest of your blog, you seem to reject Newtonian gravitation in favor
of Kepler's laws of planetary orbits. How does your model account for the
perturbations that are observed in three-body and more complex systems?

For instance, right now there is a satellite called SOHO at the Sun-Earth L_1
Lagrangian point. Why do you say that Newtonian gravity is a myth, when the
existence of such an orbit violates Kepler's third law but is in perfect
agreement with calculations according to the Newtonian model?

~~~
HelloBeautiful
<OFF TOPIC> There's a live feed from that satellite with some interesting
moments -
[http://www.youtube.com/watch?v=gpNyAtU-3Tc&feature=share](http://www.youtube.com/watch?v=gpNyAtU-3Tc&feature=share)

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d_r
This won't help me learn a new technology, build my startup quicker, or even
introduce me to others who are trying.

But it is pseudo-science babble that I might find in an e-mail forward.

Not Hacker News.

(Hit my 365 days yesterday so I am officially "allowed" to complain.)

~~~
ahlatimer
The guidelines suggest different criteria for what constitutes "Hacker News"
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