# What does antimatter look like?

I have seen simulations of antimatter on TV. Has antimatter ever been photographed?

• Those probably weren't simulations; they were probably depictions of antimatter created by artists using computers – J. Antonio Perez Nov 28 '16 at 15:53
• If "look like" was more precisely stated, it would focus the discussion quite a bit more. If it is a look like as in "detected" you got one answer; if it is a look like as in "see without aid or with only optical aid" you got a different answer. Do you consider a detection in a bubble chamber a photograph of it or you'd want enough material for a image of a macroscopic object? That would clear some of the issues presented in the answers. This is an instance of "simple questions can have complicated answers". – Vendetta Feb 28 '17 at 18:32

What does a proton look like?

Due to the kaon having interacted with a proton in the hydrogen, the rightmost beam track produces a spray of 4 tracks. The longer highlighted track is clearly dark – it has produced a higher number of bubbles per centimetre than, say, the beam tracks; this tells us that it is moving more slowly. (For details, click here.) Such tracks are a common feature in bubble chamber pictures and usually signify protons.

What does an antiproton look like?

The dark lines in this picture are produced by charged particles as they force their way through liquid deuterium.

The highlighted track is an antiproton, produced in the decay of an antilambda into an antiproton and a pion

In the top left corner of the picture, this antiproton annihilates with a proton constituent of a deuteron, producing a 6-pronged annihilation 'star’. (If it had struck a neutron, the number of prongs would, by charge conservation, have to be odd.)

What distinguishes a proton from an antiproton in the bubble chambers to start with is the charge. An antiproton can release a lot of energy which the proton cannot.

In conclusion, protons and antiprotons have been photographed, so yes, antimatter has been photographed. There have been thousands upon thousands of such pictures in the studies of elementary particle interactions.

Edit after observation in the comments that these tracks are like footprints, and not photographs of the particles.

What is a photograph? It is a permanent registration of shape in two dimensions by the interaction of scattered photons with the film.

The tracks above are much more than footprints, they are consecutive molds of the shape and mass of the passing particle ( that is why we know it is a proton by mass, the ionization dependence tells so). They are the interaction by photon exchanges of the passing particle. Microscopically each delta(x) of the track is a photo of the particle and the film is the hydrogen of the chamber, which is then photographed. So it is a photo of a photo.

• These are not photographs of antiprotons, but of their vastly larger effects. It would be like saying that a photo of contrails was the same as a photo of the UFO that produced them. – Brock Adams Nov 26 '16 at 19:19
• If you could prove that ufo s exist. We have proof that an antiproton exists ( see those tracks at the end). Everything that we see is a proxy, I see this screen because of photons hitting my retina and being interpreted by my brain as a "screen with letters". actually photos of contrails tell me that an airplane passed. At the particle level those are the photos we can take, protons or antiprotons. – anna v Nov 26 '16 at 19:37
• (Bad) epistemological tangents aside, a photo of your footprints is not the same as a photo of you, no matter what your brain does. ;) – Brock Adams Nov 26 '16 at 19:43
• Note that in Safari (at least for me) the highlights are not layered on top of the images, but instead are off to the right side. – Todd Wilcox Nov 26 '16 at 20:53
• @BrockAdams well, a mold is a three dimensional "photo", much more info than than a footprint, and the tracks in the chamber are molds, it is how the collective material "registers/photographs with interacting photons". – anna v Nov 27 '16 at 4:55

The total amount of antimatter ever created on earth is not even sufficient to be visible by eye, so it is hard to answer.

However, if a bunch of antimatter was available as stable solid or liquid material, there is no reason to think it would look different. Indeed, its interaction with visible light is pretty much exactly the same as usual matter, so it would look the same.

Update: As comments explain, the looks of a piece of antimatter would be the same of its matter counterpart. Thus it might have any colour, texture, shine, etc.

• We might add that the reason for this is that the photon is its own antiparticle, therefore we can assume it would interact with antimatter just the same it does with matter. – vsz Nov 26 '16 at 19:41
• @Pedro yes, the latter. I do agree it would be better if this answer said so explicitly, but that is what it means. – David Z Nov 27 '16 at 1:42
• @Pedro is matter grey, green, shiny, matte, liquid or solid, etc.? Do you see that matter is a broad category and all matter isn’t any one of those? Antimatter is exactly the same. An apple made of antimatter would look different than an icecube made of antimatter. – JDługosz Nov 27 '16 at 1:58
• @Pedro A cloud of anti-hydrogen would look like a cloud of hydrogen i.e. it would be invisible. A puddle of anti-water would look like a puddle of water. An Anti-Pedro would look like a Pedro. – immibis Nov 27 '16 at 3:06
• @Simon An anti-simon or an anti-me, in an anti-laboratory would probably be able to feel it. – J. Manuel Nov 28 '16 at 11:32

Antimatter looks just like matter. Experimentally, there is no difference between the spectral lines of antihydrogen and of ordinary hydrogen. Same emission spectrum.

The photon is its own antiparticle. It interacts in the same way with matter as with antimatter.

PS: Very recent Nature article by Ahmadi et al gives an upper bound of $2.10^{-10}$: http://www.nature.com/nature/journal/vaap/ncurrent/pdf/nature21040.pdf

Carl David Anderson got a Nobel prize for taking a photograph of a positron:

$\hspace{60pt}$

(Source: The Positive Electron, by C.D. Anderson). Remark: the image is a photograph of the path of the positron, as seen in a cloud chamber.

For the sake of comparison, the track as of an electron, the antiparticle of the positron, is

$\hspace{60pt}$

(Source: Energies of Cosmic-Ray Particles, by C.D Anderson)

I recommend to check out Anderson's article if you are interested in the photographs of the track of different particles, suchas $\alpha$ particles:

$\hspace{60pt}$

In any case, the general message is clear: particles and antiparticles leave the same track, except for the sign of their curvature (which is determined by the electric charge).

• Yeah, but in your first sentence you said that he got a Nobel prize for taking a photograph of a positron, not for taking a photograph of the path of a positron, so you may want to edit it to be more clear. This is kind of like posting a picture of a contrail when asked what a certain jet looks like – Kevin Wells Nov 28 '16 at 13:53
• @AccidentalFourierTransform Since you edited it without stating that it was an edition, I'll remove my previous comment since it now looks odd. – J. Manuel Nov 28 '16 at 16:00

Antimatter-antimatter interaction is, to the best of our knowledge of physics, chemically identical to matter-matter interactions. Any symmetry breaking is so small that it would have no observable effects at human scales.

Its interaction with photons is also identical.

The only important way it interacts differently is the matter-antimatter reaction, where it annihilates and releases a large amount of energy.

So the short answer is, it looks like matter. But it only looks like a matter if it is completely isolated from matter.

Doing so is very hard.

Suppose we had a 1 kg block of antimatter gold floating in interstellar space, in hard vacuum, with a particle density of 10 hydrogen atom per cm^3 at 100K (in a "filament" of gas in interstellar space).

It would form a cube just under 4 cm on a side, with a surface area of about 100 cm^2.

The speed of sound in space is about 100 km/s. This is roughly how fast the atoms in the interstellar medium are traveling.

This gives us:

100 km/s * 100 cm^2 * 1.7 * 10^-24 g/cm^3 * c^2


which is 0.15 watts.

So a 1 kg cube of anti-gold glows with the heat of 0.15 Watts in a hard vacuum. In near-Earth space, it would be a few times brighter due to the solar wind.

On Earth or in a pressurized atmosphere, it is a bit brighter: 3 * 10^17 Watts.

So a block of anti-gold floating in space would look mostly like gold. At least until you disturbed it with the residue of your rocket thrusters.

• Just commenting on "speed of sound in space" - there are no sound waves there. Otherwise I agree. – Pieter Nov 28 '16 at 20:25
• @Pieter There are and can be sound waves. They are on the scale of solar systems or way larger in wavelength. Not very "sound" like (as the frequencies are a bit ridiculously low), but they are pressure waves that propagate through a medium. The basic idea is that the highest frequency "sound" wave in a medium is the mean free path of particles in that medium. Pressure waves above that wavelength (and below the implied frequency) can behave "sound like". Near Earth, it gives something like a month-long frequency as the highest frequency. Or maybe I'm on crack. – Yakk Nov 28 '16 at 20:33
• That is extreme infrasound :) – Pieter Nov 28 '16 at 20:45
• But you seem to overestimate the velocity. Atomic hydrogen would give a speed of sound just about five times faster than in air. And it also only goes with the square root of temperature. – Pieter Nov 28 '16 at 20:52
• Described in this question (with answers) – user27542 Nov 28 '16 at 23:36

According to a very recent experiment, it looks exactly the same as normal matter (or, at least, they interact with the light spectrum in the same manner).

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