Researchers have observed the Lyman-alpha transition in the antihydrogen atom

https://home.cern/about/updates/2018/08/alpha-experiment-takes-antimatter-new-level

by sohkamyung • 8 years ago

145 38 8 years ago

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acd• 8 years ago

If there is anti matter. Is there an anti gravity force if there is gravity?

strstr• 8 years ago

No, but charges are inverted for particles vs antiparticles.

majewsky• 8 years ago

If you're thinking of "negative gravity", then particles exhibiting it fall under the "exotic matter" umbrella. We don't know what exotic matter actually is, although its existence is predicted by the current models on the expansion of the universe.

Antimatter still has regular (i.e. positive) mass, so gravity works in the usual (attracting) way.

zamalek• 8 years ago

The specific type of exotic matter would be imaginary matter, that is matter with imaginary mass (a complex number) - tachyons. Negative matter, which is also exotic but has a negative real mass, behaves normally under gravity so long as the two bodies are sufficiently different in absolute mass.

GolDDranks• 8 years ago

Basically, antimatter has it's all "quantum numbers" inverted of it's normal counterpart, but it's energy content is not inverted. Strength of gravity is a measure of the energy content, so antimatter should have normal gravity. If it doesn't that's some exciting news!

philipov3• 8 years ago

Antimatter is a consequence of quantum field theory, but all signs indicate gravity can not be successfully described as a quantum field. Gravity has properties such as having its interaction strength grow with the amount of charge (energy), which is very different from the forces described by quantum fields that have constant interaction strength. To get antigravity, you need to find a way to have negative energy without it making the vacuum unstable.

It's most typical to describe gravity as dynamical spacetime, not a field existing in that spacetime. The closest people have come to a quantum theory of gravity has been to show that in certain toy universes gravity in a bulk space is the dual of strongly-coupled field interactions existing on the boundary of that space-- that is holography. Information-theoretic approaches have have also suggested that gravity emerges as the 'hydrodynamics of entanglement.' All this suggests gravity is not a fundamental force, but is far from a coherent real-world theory at this point.

The closest to an "antigravity" in general relativity is the cosmological constant, thought to explain dark energy. Its tiny (10^-122) positive value behaves like a constant negative energy attributed to the vacuum itself, driving the exponential expansion of space.

xhrpost• 8 years ago

This is one of the aspects of theoretical physics that I find fascinating. Is there a good book on this that doesn't involve an insane amount of math? (ex. similar to BHoT)

pdonis5• 8 years ago

all signs indicate gravity can not be successfully described as a quantum field

That's not quite correct. The quantum field theory of a massless spin-2 field was developed in the 1960s and 1970s and is perfectly well-defined. The problem with it then was that it is not renormalizable; but today basically all QFTs are viewed as effective field theories anyway, which means not being renormalizable is not a showstopper.

The real issue is that we have no prospect of measuring any quantum aspects of gravity now or in the foreseeable future, so there is no way to test the QFT that has been developed against experiment.

Gravity has properties such as having its interaction strength grow with the amount of charge (energy), which is very different from the forces described by quantum fields that have constant interaction strength.

This is not correct either. The coupling constant of the massless spin-2 field is just Newton's gravitational constant (modulo some constant factors that depend on your units). The fact that the total interaction in a specific case varies with energy is no different from the fact that the total EM force between two charged objects varies with the charge. Energy is the source for gravity just as charge is the source for EM; the source is not the same as the coupling constant.

To get antigravity, you need to find a way to have negative energy without it making the vacuum unstable.

Agreed. And as far as we know that is not possible.

All this suggests gravity is not a fundamental force

This is quite possible, yes, but even if it were true it would not necessarily make the spin-2 massless QFT I referred to above invalid; it would just make it an effective theory that emerges from whatever is the next level down. (Which, as I noted above, is basically how we view all QFTs today anyway, including the Standard Model of particle physics.)

The closest to an "antigravity" in general relativity is the cosmological constant, thought to explain dark energy. Its tiny (10^-122) positive value behaves like a constant negative energy attributed to the vacuum itself, driving the exponential expansion of space.

No, a positive CC does not have negative energy. It has positive energy and negative pressure. The effective source in the Friedmann equation is the energy density plus three times the pressure, which for a positive CC is negative (because the negative pressure outweighs the positive energy density).

ianai• 8 years ago

I skimmed and didn’t find it. Is the frequency the same as hydrogen?

cardinalfang• 8 years ago

It mentions "good agreement". They are working on increasing the accuracy of the measurements to the point where they can confirm this.

gus_massa2• 8 years ago

From the abstract of the paper: http://www.nature.com/articles/s41586-018-0435-1

The transition frequency at a field of 1.033 tesla was determined to be 2,466,051.7 ± 0.12 gigahertz (1σ uncertainty) and agrees with the prediction for hydrogen to a precision of 5E−8.

I.E. It's the same for all practical purposes, but there may be a extremely tiny difference.

Edit: Comparing the numbers with the results for Hydrogen in an article someone else linked here

  Anti-Hydrogen:      2,466,051.7 ± 0.12 GHz
  (Normal)-Hydrogen:  2,466,061.413187035(10) GHz

So they measure a tiny difference, and looking at the error estimations the difference is significative. I'm not sure if that is an expected difference or a unexpected difference or just an error in the experiment.

Blackbeard_2• 8 years ago

That would be more than a 5 sigma difference which would definitely be significant but that number you're quoting for normal hydrogren is the 1S-2S line.

This measurement is the 1S-2P line which has an average frequency of ~2,466,051.625 GHz (there's actually two levels). Which agrees to within 1 sigma - i.e. good agreement.

japanuspus• 8 years ago

As an atomic physicist, it is great to see clever atomic physics experiments opening up new fields in high-energy physics. The team has been working incredibly hard for this: Jeff Hangst who leads the experiment was already working on this when he taught my undergrad electrodynamics course back in 1998!

An important piece of background info for non-atomic-physicists is that the Hydrogen 1S-2S transition frequency is probably the most accurately measured physical property in the world, thanks to the pioneering work by T. Hansch. Back in 2011 they reported an uncertainty of 4e-12, https://arxiv.org/abs/1107.3101.

stargazer-3• 8 years ago

The abstract says 4e-15, not 4-12?

windows_tips• 8 years ago

So does the paper. The paper also says this, right before explaining that it's a component of the ~4e-15 number, though:

A conservative estimate of the height difference between clock and experiment contributes a gravitational red shift uncertainty of 7.7 × 10−17.

So, it appears the 4e-15 is not an actual measured value, but a synthetic value based on estimation and measurement.

MeteorMarc• 8 years ago

Awesome. I share your admiration for such long quests and it reminds me of a similar quest to reach Bose Einstein Condensation of atomic hydrogen, the basis for the mentioned hires spectroscopy. See: https://cds.cern.ch/record/375046/files/9812038.pdf

jschwartzi• 8 years ago

I thought the charge on an electron had been measured out to 10^-19? One of my professors posted the journal article from the NIST team that did so.

Here's a reference: https://physics.nist.gov/cgi-bin/cuu/Value?e

reacweb• 8 years ago

Your reference gives an uncertainty of 6.1 x 10-9

ajuc• 8 years ago

I always wondered how they put atoms in magnetic traps, isn't hydrogen 1 positron + 1 antiproton? It should be neutral?

castratikron2• 8 years ago

It's electrically neutral, but it still has a magnetic moment.

iamgopal• 8 years ago

Because electron is moving and proton not ?

ArtWomb• 8 years ago

A step closer to unlocking the secret origins of matter itself. Some deep background on the anti-matter imbalance as well as famed Soviet dissident Andrei Sakharov's conditions:

The Mystery Of The Matter Asymmetry

https://www.vanderbilt.edu/AnS/physics/panvini/babar/sakharo...

sulam• 8 years ago

I read this entire article with some interest, but made the (naive) assumption that it would actually speak about the conditions under which Sakharov made his contributions to matter/anti-matter imbalance. Instead I learned something new, which is that there exist a set of conditions Sakharov identified that must be accounted for in any theory that addresses this imbalance. Don't read it expecting to learn about Sakharov's life. :)

Researchers have observed the Lyman-alpha transition in the antihydrogen atom

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