
New antimatter gravity experiments begin at CERN - lainon
https://home.cern/about/updates/2018/11/new-antimatter-gravity-experiments-begin-cern
======
wcoenen
If anti-matter would be found to be affected differently by gravity, then that
would be a big problem for general relativity wouldn't it? If gravity is
warped spacetime geometry, then it has to affect the path of all particles in
the same way.

~~~
snarfy
If anti-matter is regular matter moving backwards through time, it seems it
should 'fall' upward.

~~~
ridiculous_fish
No, gravity is time symmetric!

Imagine throwing a ball up, and watching it fall back to your hand. Run the
clock backwards and it looks exactly the same!

~~~
zeven7
But if you just hold out a ball and drop it, it won't look the same in
reverse.

~~~
ridiculous_fish
It will! Imagine the ball right before it hits the ground: it will have a
large downward velocity. Reverse time and the ball acquires an upwards
velocity, that slows as it reaches your hand, exactly as if it's accelerating
towards the earth.

If you know some calculus, observe that Newtonian gravity is coupled to
acceleration but NOT velocity:

    
    
        d^2 x / dt^2 = a = g
    

Now run time backwards: let dt be negative. This doesn't change a, because dt
is squared and squaring a negative is still positive. The acceleration is
independent of the direction of time.

To show this isn't just mathematical hand-waving: consider a magnetic field.
This does couple to velocity. Reverse time, and the magnetic field pushes the
other way. Electromagnetism is not time symmetric, it's time ANTI-symmetric.
Gravity is different from EM in this respect.

~~~
zeven7
Ok, interesting. The gravity part makes sense.

I don't understand the difference with magnetism though. Let's say you have a
positively charged item and you're standing on top of a large negatively
charged surface. You "drop" the positively charged item. How does its velocity
over time differ from the gravity example? And how is it different with time
reversed? Seems like it would be the same to me... In forward motion, it would
accelerate until it collided with the surface. With time reversed, it would
start with a fast velocity and slow down over time.

Edit: I googled this. It sounds like the motion of magnetized bodies is time
symmetric, but when the charge of the electric field produced by the motion is
taken into account it has to be reversed. Is this correct?

~~~
ridiculous_fish
In classical electromagnetism, we separate the electric field E and the
magnetic field B.

If we isolate E, we get rest: electrostatics. Charged particles exert an
attractive or repelling force in proportion to their charge, just like
gravity, except charge instead of mass. So E is time-symmetric. This applies
to your example.

Now consider just B. A positively charged particle is moving to the left,
through a magnetic field that points inwards. By the right-hand rule, the
force on the particle is up. Reverse time: now the particle is moving to the
right, so you rotate your hand 180 degrees and the force is downwards. This
magnetic field produced an upwards force forwards in time and a downwards
force backwards in time: it's antisymmetric.

Put mathematically we have:

    
    
       F = qv x B
    

where q is the charge, v is the velocity, B is the field. Reverse time and the
velocity gets a minus sign, so F reverses.

So E is symmetric and B is anti-symmetric.

~~~
blueprint
What makes it the right-hand rule rather than the left-hand rule?

~~~
ridiculous_fish
Positive charges obey the right hand rule, while negative particles obey the
left hand rule. Classical EM doesn't distinguish between these, and we might
as well reverse the signs and hands.

QM does so distinguish, for reasons way beyond me.

~~~
blueprint
Seems like a very important/foundational answer to know, though. Do you happen
to know of anything I can read about why charged particles behave by that
rule?

~~~
snarfy
[https://www.youtube.com/watch?v=0mXW1zPlxEE](https://www.youtube.com/watch?v=0mXW1zPlxEE)

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

------
saagarjha
Forgive me if this sounds presumptuous, but is this experiment literally
trying to answer "does antimatter attract normal matter"? To me, this seems
like a pretty simple thing to test–why hasn't this been done before?

~~~
jessriedel
The strength of the gravity between a proton and an (anti-)proton is 30+
orders of magnitude weaker than electromagnetism. The only reason we are able
to notice gravity at all is because the electromagnetic forces between
macroscopic amounts of matter (~10^23 protons) cancel out essentially
perfectly, leaving only the gravitational force remaining. But the amounts of
antimatter we can create and collect is extremely microscopic, so we can't use
this canceling trick. Furthermore, we can't keep antimatter from annihilating
for long enough to take long detailed measurements.

~~~
saagarjha
Why not use neutrons and antineutrons, or any other neutral particle that has
mass?

~~~
jessriedel
Antimatter is generated at extremely high (relativistic) speeds and generally
has to be slowed down ("cooled") in order to make careful measurements or to
even collect multiple particles together. And that can't be done unless you
can steer the particle with electromagnetism.

If you just generated individual relativistic anti-neutrons and tried to watch
them follow ballistic trajectories in gravity, I suspect they'd just look like
perfectly straight lines up to the limits of your detector resolution. Not
sure though.

(The only other quasi-stable neutral particles are neutrinos, and those are
essentially non-interacting with any detector. They leave relativistically and
you'll never see them again.)

~~~
phyzome
Neutrons can be contained in a magnetic bottle, even if they don't last long
in isolation. Presumably the same is true for antineutrons, although I don't
know how hard it would be to slow them with magnetic fields...

~~~
jessriedel
Yea, thanks for mentioning. I believe those bottles only work when the
neutrons are already at very slow speeds. They exploit the strong force and
the residual electromagnetic "handle" neutrons have by virtue of being built
from charged components (quarks), which leave them with a magnetic dipole
moment.

------
mlindner
The title can be misleading if it is not read literally (or your brain tries
to fill in extra information). This is testing the effects of gravity on
antimatter, NOT antigravity testing.

~~~
nsxwolf
Does anyone expect it to behave any differently than matter?

~~~
spenczar5
Almost all physicists think it should be no different, but a few think
antimatter might gravitationally repel normal matter. See
[https://en.wikipedia.org/wiki/Gravitational_interaction_of_a...](https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter).

~~~
jp555
So antimatter warps space in opposite way that matter does? Then you’d
probably then need a negative-Earth-mass amount to counteract the depth of the
earth-mass caused gravity-well we’re in.

The antimatter mass equal to our planet is a lot of antimatter. Rockets, even
antimatter powered ones, seem a lot better way out of Earth’s well.

~~~
Jyaif
> Then you’d probably then need a negative-Earth-mass amount

Assuming antiparticles are "repulsed" by earth's gravity, 1.01kg of antimatter
would be enough to take 1kg of matter to space.

~~~
Pxtl
The trick would be to attach them together with causing a nuclear explosion.

~~~
louthy
Oh the humanity!

------
mrfusion
If Antimatter were to have antigravity could you bust up a black hole by
filling it with antimatter?

~~~
qubex
A black hole is a creature of pure self-sustaining curvature — the field
itself has enough energy in it to maintain the warpage (as the singularity
presumably at the core is beyond the event horizon and gravity, like
everything else, cannot escape it’s own grip and emanate from the singularity
to the event horizon where we observe the effects).

So tossing in antimatter would not do much. It would never cross the horizon
in an external observer’s reference frame and thus would never interact with
anything and thus would produce no effects.

Besides we know that when matter and antimatter react, they emit energy that
has positive sign, not zero... twice the value of any particle’s mass. That in
turn implies that matter and antimatter have the same sign of energy despite
opposite charge.

Furthermore by coupling attractive matter and repulsive antimatter one could
create a perpetually-accelerating device as the repulsive antimatter would try
to escape the matter and the matter would chase after it. This obviously is
cause for concern (but in general General Relativity does not conserve energy,
so it’s not incompatible with the theory per se — just very dubious).

I’m expecting the antimatter to fall downwards just as matter would. But the
whole point of science is to check that what you expect conforms to what the
universe actually does. So this is definitely not a waste of resources: much
the contrary, it’s a vitally important measurement to make.

~~~
krohling
I don't this is exactly accurate. Hawking radiation for example, causes black
holes to evaporate over time. While the radiation that is detected outside the
black hole has positive mass/energy the in-falling anti-particles have
negative mass/energy which results in the net reduction of the black hole's
mass/size. Does it not then make sense that in-falling anti-matter would have
an evaporating effect?

~~~
qubex
The “one of the virtual particles of the pair created in the vicinity of the
black hole’s horizon falling in leaving the other one to escape to infinity as
radiation whose mass-energy must be subtracted from that of the black hole”
view of Hawking radiation is a pedagogical construct thought up by Hawking
himself after calculating the effect by other means for the sake of public
promulgation. In reality it has to do with the restriction of the resonant
modes of quantum fields imposed by having a border (horizon). Case in point:
if the full truth were that of infalling versus escaping virtual particles
there’d be a definite trajectory associated with the escaping particle that
would convey information about where, approximately, the virtual
particle/antiparticle pair popped into existence, violating Heisenberg
uncertainty. In reality, Hawking radiation has wavelengths comparable to the
diameter of the black hole that make it impossible even in theory to resolve
where the supposed particle/antiparticle pair “popped” into existence,
preserving the uncertainty principle. This is also why radiation becomes more
energetic as the hole shrinks in size: that’s because the associated diameter
shrinks and allows wavelengths of emitted radiation to contract, packing more
energy into those waves. If it really were particle/antiparticle being shorn
apart by the hole’s gravitational attraction you’d expect more radiation to be
emitted by a big hole (vacuum activity per volume area being constant, and
thus a bigger hole would border more unit volumes and allow for greater
interaction with the quantum vacuum that would slow down as it shrank).

~~~
XorNot
Hang on, Heisenberg's uncertainty principle doesn't need to be preserved with
virtual particle/anti-particle pairs - that's the point of Hawking radiation -
the particles are no longer virtual, and so much must acquire a real value of
energy from somewhere (and do so from the mass energy of the black-hole).

You're very much trying to draw a line here that QM doesn't support -
everything is a particle and a wave at the same time, and the interpretation
that one pair of a particle in-falls is at least as valid as the
interpretation that it's to do with the exclusion of wavelengths.

EDIT: For example, the proposed argument with bigger black holes falls down by
a similar interpretation to the wavelengths - for virtual particle pairs with
sufficient initial velocity to escape the gravity of the black hole, the
initial location of them by necessity becomes very indeterminate, or their
mass very light - in both cases making it progressively less likely with black
hole size that one part of the pair appears initially inside the black hole
event horizon, or makes the resulting energy of the radiation less and less.

------
markovbot
OT: Why does CERN need a TLD? I'm not complaining, it just seems like an odd
(and expensive) thing to have.

~~~
anyfoo
Given that the literally first web server was at CERN, I hope they get a
special price for their TLD.

~~~
kgwgk
Domain names, even .com, predate the web by many years. We could be using
gopher in our smartphones instead if things had happened differently :-)

~~~
anyfoo
Oh, I remember gopher, and I wasn't implying that CERN invented the domain
name system. Just that they deserve their own TLD.

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gmueckl
So these experiments are about to be ready to run just as their feeding
accelerators will be shut down for two years? That timing certainly sucks for
all the PhD students involved.

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imh
To be perfectly clear, is this testing how antimatter and matter interact
gravitationally, or is it testing how antimatter and antimatter interact
gravitationally?

~~~
dustycat
It's testing how antimatter and matter interact gravitationally.

It isn't possible to test how antimatter and antimatter interact
gravitationally, because only single atoms of antimatter can be produced, and
single atoms don't exert enough gravitational pull on each other to be
measurable.

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throwaway487548
Simulation (using the tools made according to some mathematical model) is not
an experiment by definition, the very same way a cartoon is not reality.

------
bbeonx
I don't know why people keep posting about this. It really doesn't matter

~~~
aidos
Is that a pun?

------
Asturaz
Hope not Gordon Freeman fails an experiment...

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ionwake
Assuming anti-matter is discovered - are there any public listed companies
which I could invest in right now?

~~~
krapp
Antimatter was discovered a long time ago... it's used in PET scanners among
other things.

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egfx
How do you think UFO's move through earth's atmosphere? They repel matter via
real-time manifold dynamics allowing them to move at supersonic speed. I think
we already know this.

~~~
ppppppaul
yes

~~~
pp19dd
Hm. I'm a skeptic and I typically hit all the standard checkmarks on
dismissing nutjobs. It's almost a mental stamp worn down to the nubs. But this
right here reminded me of the time I scratched my head.

Cue the weird release of the NYT pieces on Navy recordings of UFOs released
over the past year. Did you happen to see that one? If not, look it up. There
were basically two FLIR recordings of something pretty spooky and, wow, it was
something else. The videos were followed up by a leaked NIMITZ carrier group
report of the incident cataloging and verifying pretty much everything the
pilots said in the interview. The pilots were made fun of by their peers.
Means of propulsion in the video was nothing like I'd ever seen anywhere
before. The Navy basically said "we don't know what this is" and "it
demonstrated propulsion capabilities beyond any known means." One of the
videos is downright spooky in places.

First thing skeptical me did was check the provenance of the videos
themselves. They were directly provided to NYT by a weird organization headed
by an ex band member from Blink 182. Nutjobs, check.

Second thing I checked was who the writers of the article were. One was a
general assignment reporter (meh, they have to put someone on it and they were
all out of stolen tomato plant stories that day), another was a has-been
burnout whose name got used to elevate the story, and last author was a person
who wrote books on ghosts and spirituality or some such. Cranks, check.

Then WaPo and other orgs released a bunch of regurgitated hashes of the same
story. So I sifted through to see if there were any more details. Nope, they
were all borrowed from NYT. Nothing original, lazy re-reporting, check.

Then just to be sure the guy was just lazy I reached out to a WaPo reporter.
Nothing.

Then two weeks went by.

He got back to me and told me that they got caught with their pants down. They
had been working on the story long before NYT published it - in cooperation
with the bizarre group with the ex-Blink 182 guy, and WaPo were under the
false impression that they had an exclusive story with them. So when NYT's
came out, they felt betrayed and buried what work they had and scrambled to
get their own GA reporter to finish the deal. Not lazy. They just cut their
losses best they could.

Here's the kicker. The guy verified the provenance of the flight cameras. They
WERE provided by the Pentagon under a FOIA act request. Despite the fact that
NYT's videos were provided by the Blink 182 people, WaPo had an independent
copy of it obtained from the military.

The part that made me scratch my head was that it wasn't just an empty boast.
I was given a tip on making a very specific FOIA request to the Pentagon. Goes
something like "query seeking cockpit videos cleared for release to Luis
Elizondo in the Fall of 2017 (Sep-Oct)."

So what of it? Well, our high energy physics people are making discoveries,
and while I don't know what to make any of this, for the first time in awhile
I'm feeling like we're making some forward progress in science that might make
its way to engineering, or our understanding of its limits. Just recently
scientists identified 2-3 candidate anomalies as potential new particles
(sigh, some reporters kept calling it a ghost particle). Maybe something will
come of it, maybe not. But we're trying, and once these are eliminated there
will be more observations, more research, more science. We still have a very
poor understanding of gravity and how it relates to things we feel we know.

But for once in this horrible climate we find ourselves in, both political and
social, I'm feeling optimistic that we're even looking.

[1] Interview with the pilot:
[https://www.nytimes.com/2017/12/16/us/politics/unidentified-...](https://www.nytimes.com/2017/12/16/us/politics/unidentified-
flying-object-navy.html) [2] Leaked NIMITZ report (PDF):
[https://media.lasvegasnow.com/nxsglobal/lasvegasnow/document...](https://media.lasvegasnow.com/nxsglobal/lasvegasnow/document_dev/2018/05/18/TIC%20TAC%20UFO%20EXECUTIVE%20REPORT_1526682843046_42960218_ver1.0.pdf)

~~~
HeadsUpHigh
The flir stuff was debunked but I don't remember the details.

~~~
pp19dd
Details please? As far as I know neither NYT nor WaPo nor others have issued
any retractions.

~~~
HeadsUpHigh
There was a link on a Joe Rogan Experience podcast but I'm having a hard time
finding right now as there are multiple clips of him talking about UFOs.

~~~
pp19dd
Hm. So again, my whole rant has to do with the fact that the videos (3-4 in
total?) have been independently verified to have come from the Pentagon. That
part has not, to my knowledge, been debunked as independent sources have
FOIA'd copies of it. Heck, you could file a request as a private citizen and
obtain the same, and I encourage you to.

So what does this really mean? If you draw it down to either the video being
fake or real, I can only see four possibilities and reasons.

1\. Fake: this is a product of a Pentagon psyop intended to leak out and cast
doubt on our enemies's intelligence, implying that we have access to top
secret propulsion technologies beyond their known capabilities.

2\. Fake, but conducted by persons unknown and planted inside the Pentagon. It
would have taken quite an effort to fabricate because it involved two-three
radar tracking stations, an entire naval carrier group, senior pilots,
military intelligence, record keeping personnel. Too many of these have issued
reports corroborating the observations. Way too many disconnected people to
manage for a conspiracy.

3\. Real. One of our enemies has access to secret propulsion technologies
beyond our capabilities to counter. Enemies, because our own military
intelligence was unaware of anything like this and a threat, because it
clearly had superior flight characteristics as described by the witnesses.

4\. Real. Question is about its origin, however. Terrestrial: are these merely
shy biologicals living under the sea we've never cataloged? Extra-terrestrial:
automated probes from another place, another time? Other life in the universe?

Only one of these possibilities is bland to a point of ignoring it, that being
#1. Rest of the possibilities have profound implications about ourselves, and
none so much as #4. It means we're not alone in the universe. So while I agree
that a broken clock can tell the right time twice a day, I don't bash what I
used to call UFO nutjobs as much anymore.

~~~
egfx
I don't see why there can't be a fifth possibility.

Real: technology our own military (USA) has had access to for years, and what
we see in the video is a test to see how our own pilots would react.

I'm personally leaning in this direction.

But just wanted to say. Reading through the document. The idea that these
things cloak themselves when observed is something that I haven't heard and
more mind blowing then anything. And the notion that these are technologically
advanced beings from our oceans is under scrutinized.

~~~
xattt
It would explain the incoherent speech of the last video.

------
adamredwoods
>>At this point, the neutral antiatoms will be released from the trap and
allowed to fall from a height of 20 centimetres, during which the researchers
will monitor their behaviour.

Assuming it falls, and doesn't tear open the time-space continuum.

