[Matteroftime (OP)]

Hello everyone, they are currently different experiments in the CERN to see how antimatter behave with the gravitational field of our Earth, i was thinking, what if they do not find any gravitational interaction between matter and antimatter? It would be interesting to test the gravitational interaction between antimatter and antimatter.
Would it be possible then that matter attracts matter, antimatter repulses antimatter, with no gravitational interaction between them.
In this case, time would be in some sense reversible, going backwards to the past matter repulses matter, antimatter attracts antimatter. That would also explain why we do not find anti matter.
It would be also possible then that the big bang is the "center" of two opposite timelines one made of matter galaxies to the future, the other made of antimatter galaxies to the past.
I am no physicist, thank you for your help and comments

[evan_au]

Would it be possible then that matter attracts matter, antimatter repulses antimatter

I think the general expectation is that:

• Matter attracts matter
  
• Antimatter attracts antimatter (but we don't have nearly enough antimatter to measure it's gravitational interaction with other antimatter)

It is the interaction between matter and anti-matter that is a question of some debate, and is the subject of ongoing experiments at CERN.

According to Gerard 't Hooft, every physicist recognizes immediately what is wrong with the idea of gravitational repulsion: if we throw a ball high up in the air so that it falls back, then its motion is symmetric under time-reversal; and therefore, the ball falls also down in opposite time-direction. Since a matter particle in opposite time-direction is an antiparticle, this proves according to 't Hooft that antimatter falls down on earth just like "normal" matter. However, Cabbolet replied that 't Hooft's argument is false, and only proves that an anti-ball falls down on an anti-earth - which is not disputed

For an overview, see: https://en.wikipedia.org/wiki/Gravitational_interaction_of_antimatter

For published progress at CERN, see the AEGIS, ATRAP and ALPHA  links at: http://home.cern/topics/antimatter

[jeffreyH]

The graviton should be its own anti-particle so whether in a matter or anti-matter universe the effect of gravity should be the same.

[Matteroftime (OP)]

Thank you for your answers, your quote from wikipedia is interesting, if we throw up a ball it comes back in our direction in time, a matter ball goes back to a matter earth. It does not mean that an antimatter ball would do the same on a antimatter earth in our direction in time (to the future i mean), if an anti particle is a particle going in the opposite direction in time the movement should be the opposite.
That is why i do not understand why it is expected that anti matter should attracts antimatter in our direction in time.

Concerning the graviton, i believe it is still a hypothetical particle.

There is a link between time and mass, time has a "direction" is it possible that gravity is a kind of link that differenciates matter from antimatter?

[jeffreyH]

A particle is considered to be an excitation in a field. Since LIGO detected a gravitational wave which can be considered to be an ensemble of excitations in a field then the evidence is swayed heavily in favour of the existence of the graviton.

[puppypower]

One experiment we can run, is to measure the impact of gravity on an atom before and after beta-decay. In beta decay, an atom will give off a positron, which had been existing, stably, inside the nucleus.

The positron is the anti-particle of the electron. In beta decay the atom makes a positron without making an electron therefore we can focus on the anti-matter. If matter and anti-matter are under gravity and anti-gravity, respectively, the atom should weight more before it gives off the positron, and it should get heavier after the positron is released, since the positron should cancel part of the gravity, with anti-gravity, in the starting atom. 

For example, below if the positron is under anti-gravity, N14 should get heavier than C14, due to getting rid of a trace amount of anti-gravity.

[PmbPhy]

Hello everyone, they are currently different experiments in the CERN to see how antimatter behave with the gravitational field of our Earth, i was thinking, what if they do not find any gravitational interaction between matter and antimatter?

That's quite an odd experiment. The inertial mass of a particle is identical to the mass of that particles antiparticle and since inertial mass equal gravitational mass there is no reason to believe that an antiparticle should fall at a rate which is different than its counter particle. In fact there is no distinction between a particle and its antiparticle, this convention is arbitrary. Which particle is referred to as the particle and which is referred to as the antiparticle is merely a matter of convention.

Would it be possible then that matter attracts matter, antimatter repulses antimatter, with no gravitational interaction between them.

No, because its not possible to consider a particle and determine if its an antiparticle or not. The only thing possible is to compare it with other particles and if one particle has all of its defining constants such as its mass, charge, spin, baryon number, etc. opposite to it then you have a particle/antiparticle pair. Which one you refer to as the antiparticle is arbitrary.

[evan_au]

¹⁴C → ¹⁴N + β

It looks like the neutrino has been left out, so the equation should be more like:
¹⁴C → ¹⁴N +β^- +ν_e +156keV

I tried to do the calculation suggested by puppypower, but without much success! (help, please?)

The following masses are in atomic mass units(amu):

• ¹⁴C mass: 14.003241989
• ¹⁴N mass: 14.003074004
  
• β^- mass: 0.000548579
  
• 156 kEV equivalent mass: 0.000168
  
• ν_e mass: <0.002keV (ie very small)
  

I calculate the right-hand side to have a mass of 14.00379015 amu, which is more than the 14.003241989 amu of ¹⁴C we started with.
Since energy can't be created out of nothing, I assume I have made a mistake here, somewhere! Where have I gone wrong?

But it seems that this β particle is not a positron, but is an electron, so you can't use this to estimate the mass of antimatter.

Perhaps I should start again, using an example like the following (only it is now getting too late...):
²³Mg → ²³Na + e⁺ + ν_e +??? keV

In beta decay, an atom will give off a positron, which had been existing, stably, inside the nucleus.

Carbon 14 has a half-life of 5730 years, which makes it very useful for carbon dating.

The ¹⁴C consists of 6 protons and 8 neutrons. It's a bit of a stretch to say that the positron exists as a separate particle inside the nucleus all this time.

In a sense, ¹⁴C decay is similar to neutron decay, where an isolated neutron decays into a proton, an electron and a neutrino after around 15 minutes. Only in this case, the neutron is partially stabilized by it's environment inside the carbon nucleus. 

[Matteroftime (OP)]

Thank you for your answers,
Puppypower, i am sorry i do not get the positron existing inside the nucleus. But i think i understand that the total "weight" should be the same. If the N14 has the same weight it would mean that antimatter does not have gravitational interaction with matter. If the N14 is heavier it means that matter repulses antimatter. Is it this idea?

Pmbphy, if i understand we assume that inertial mass is the same thing than gravitational mass, so antimatter should fall the same, right? I am sorry i do not understand the second part, what is arbitrary?

evan_au, isn't it c14 mass = n14 mass + 157kev mass + ve mass? The mass of the positron is apart?

[PmbPhy]

Pmbphy, if i understand we assume that inertial mass is the same thing than gravitational mass, so antimatter should fall the same, right?

Right. That holds for all particles. There's no reason to expect a positron (the antiparticle of the electron) to fall at a different rate than anything else. However, if, for some bizarre reason, certain particles fell at different rates than 9.8 m/s^2 then general relativity would have to be modified.

I am sorry i do not understand the second part, what is arbitrary?

What is arbitrary is which particles are referred to as normal "particles" and which particles are referred to as "antiparticles." For instance the positron is said to be the antiparticle of the electron. It's also true that the electron is the antiparticle of the positron. So which particle is defined to be an "antiparticle" is completely arbitrary. The choices made as to which is which came about due to historical reasons only.

Here is the way that Dr. Matt Strassler explains it. From: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/

There are many confusions about antiparticles. You cannot look at an object and say whether it is a particle or an anti-particle; you can only say X is an anti-particle of Y, and so Y is an anti-particle of X. You can’t say Y is the particle and X is the anti-particle, or vice versa.

I highly recommend reading the rest of what he wrote. It's quite educational and very well written.  Anyway, that is precisely what I meant when I said In fact there is no distinction between a particle and its antiparticle, this convention is arbitrary. Most people don't know about this.

Another common misbelief about antimatter is particle/antiparticle annihilation. It appears that most layman, even some professional physicists, believe that when a particle is near its antiparticle the two will annihilate and yield only photons. That's wrong.

[Matteroftime (OP)]

Thank you for your link Pmbphy,
If i got what is written, whatever happens the total of energy is conserved, then everything is possible, motion energy, mass, can appear or disappear. The case with the two photons in the end is quite elegant. i think e=mc2 shows it well. And ok if a particle and its antiparticle it does not end everytime with photons.
But still, i am sorry i do not understand what is arbitrary, we live in a world mostly full of matter, if an antimatter asteroid collides with us it will definitly hurt more than the same one matter made. There must be some kind of link with the direction of time in it. (Maybe the speed squared in e=mc2 there is no direction in time in this thing)
In the end, let us consider a ball on the ground of the earth, the two things are mostly matter made, and attracting each other towards the future, in some way they can be seen as anti matter objects attracting each other towards the past. See what i mean? If litterally an antiparticle of a particle is the same one going backwards in time, then maybe we could see a distant planet anti matter made with an anti ball going up like a movie rewinding because we are heading to the future.That is why i think maybe inertial mass and gravitational mass are different things. In this case matter and anti matter cannot interact gravitationnally because if we consider a matter made ball just near an antimatter made planet if there is an interaction it would not be reversible in time. Matter and antimatter cannot attract (or repulse) in both future and past...
Still see what i mean? I am sorry, i am not a physicist and it is difficult for me.

[PmbPhy]

Thank you for your link Pmbphy,

You're quite welcome. It's my pleasure.

If i got what is written, whatever happens the total of energy is conserved, then everything is possible, ...

Not really. There are other conservation laws in physics such as conservation of momentum, angular momentum, baryon number, charge, etc.

But still, i am sorry i do not understand what is arbitrary, ...

Here's an example. Consider the following two particles: electron and positron. Whether you choose to call the electron or the positron an antiparticle is purely a matter of convention. You can choose either one. Said in another way "the choice of one or the other to be called an 'antiparticle' is arbitrary". All I'm saying is that its not important which particle of a particle/antiparticle pair is called the particle and which is called the antiparticle. If you don't understand now then forget that I used the term "arbitrary" and in its place put "merely a convention".  These conventions have been chosen by particle physicists and will never be changed. One thing to keep in mind is that if one particle is called the "particle" then the particle having all the opposite numbers of that particle then that's the one called the antiparticle.

we live in a world mostly full of matter, if an antimatter asteroid collides with us it will definitly hurt more than the same one matter made.

That's true. What it would be to say that an asteroid is made of antimatter means that all the particles in it are the antiparticles of the particles that earth is made of. I.e. matter is made of protons, neutrons and electrons. An antimatter asteroid would be made of positrons, antiprotons and antineutrons. However we could call all the particles on earth positrons, antiprotons and antineutrons and all the particles that the asteroid is made of electrons, protons and neutrons. They'd still be matter colliding with antimatter.

In the end, let us consider a ball on the ground of the earth, the two things are mostly matter made, and attracting each other towards the future, in some way they can be seen as anti matter objects attracting each other towards the past. See what i mean?

Yes. You thought that the convention of which particle is called the antiparticle is not written in stone. It is. When the particle physicists discover a particle then its known that there exists, or can be created, a particle that has opposite properties such as charge, spin, etc. Which is called the particle and which is called the antiparticle is defined when its discovered and does not change after that.

If litterally an antiparticle of a particle is the same one going backwards in time, ...

Richard Feynman came up with that idea but merely as a joke. It was never to be taken seriously. I suggest that you don't think of things in those terms.

[jeffreyH]

A lot of the time non scientists like us will pick up on the quirky aspects of a theory and focus on that without understanding why that quirky conclusion was reached in the first place. Just like the idea of an antiparticle going backwards in time. Popular science books don't help much in this regard. It is always good to question what you think you know as it is so easy to misconceive aspects of science.