Could Dark Matter/Energy be the byproduct of annihilation?

[Jake_w1044]

I’m not super familiar with the physics of this but, from a statistical standpoint it would make sense since so much annihilation was taking place after the Big Bang, and most of our universe is dark energy and matter. Further we know annihilation creates energy why not the opposite of energy it’s dark form.
I just wanna know if there is physical proof why this is not supported.

 

[Ibix]

Neither dark matter nor dark energy behave like the products of matter/antimatter reactions, which are "radiation" in the classification scheme used in cosmology. Dark matter behaves like matter but only interacting gravitationally and dark energy behaves like, well, dark energy. If either behaved like radiation they would not have the effects attributed to them.

Dark energy is not "the opposite of energy", by the way.

 

[Drakkith]

Further we know annihilation creates energy why not the opposite of energy it’s dark form.

Annihilation does not create energy. When two particles annihilate the products are always other particles (which includes photons). These particles have a combined energy (including energy contained in its rest mass, if any, along with things like kinetic energy) that is equal to the sum of the energy of annihilating particles. So an electron that annihilates with a positron with negligible kinetic energy between them usually produces two photons with energies of 0.511 MeV of energy each (equal to the rest mass of each particle in this case). But it is also possible for the annihilation to produce neutrinos, which have mass and carry away energy in the form of kinetic energy. Annihilation of heavier particles can produce loads of other particles.

Long story short, energy is conserved in annihilation reactions, so no energy is ever created or destroyed.

I just wanna know if there is physical proof why this is not supported.

Yes. We produce and annihilate particles all the time in particle colliders and have never found a measurable energy loss in these reactions.

 

[Jake_w1044]

Ok, that makes a lot more sense. Appreciate the response

 

[ohwilleke]

I’m not super familiar with the physics of this but, from a statistical standpoint it would make sense since so much annihilation was taking place after the Big Bang, and most of our universe is dark energy and matter. Further we know annihilation creates energy why not the opposite of energy it’s dark form.
I just wanna know if there is physical proof why this is not supported.

Dark Energy

Dark energy cannot be derived from annihilation if this model is the correct description of the universe. The amount of dark energy in the universe is not constant. It grows every day as the size of the universe (sometimes if we are being careful, we call it the "observable universe") constantly expands at the speed of light in every direction adding new dark energy at the horizon of the universe as it does so.

Dark energy is not the opposite of "ordinary" energy. We say something is "dark" because we can't detect it with our normal scientific tools like telescopes and microscopes and other sophisticated scientific experiments. It is not anti-energy. It is just mass-energy that we can't directly observe.

The only properties of "dark energy" are that the amount of dark energy per a given volume of space (i.e. its mass-energy density) is exactly or almost exactly the same everywhere, that this mass-energy density doesn't change over time in a way that we can detect, and that its only interaction with other mass or energy in the universe is through gravitational interactions.

Sometimes it is helpful to think about dark energy as the intrinsic curvature of space-time, rather than as actual "stuff". But for the time being, we will stick with the explanation of dark energy as "stuff" because it is easier to explain that way.

The mass-energy density of dark energy is extremely tiny. Its mass-energy density is estimated to be roughly 10⁻²⁷ kg/m³. So, there is only the gravitational mass-energy equivalent of a gram of it in a cube of empty space that is 100,000 km on each side, and it is spread evenly over that volume of space.

Imagine a cube of empty space almost big enough to hold the planet Saturn, so that it peeps out of the faces of the cube a little. Then, drop one gram of dark energy into that cube and spread it perfectly evenly everywhere within that cube. This is how diffuse dark energy appears to be.

It isn't even noticeable in systems as large as whole galaxies.

But, because it is literally everywhere, and most of the universe is empty space, the total amount of its gravitational pull adds up.

Pretty much the only discernible effect of dark energy is that the universe seems to be expanding faster than it would in a universe without dark energy.

Dark Matter

An annihilation of particles, in contrast, leaves the total amount of mass-energy in the universe (converting mass to energy at the rate of E=mc²) constant.

Unlike dark energy, the amount of dark matter in the universe is hypothesized to be constant or very nearly so. So, dark matter could have come into being by some kind of mass-energy conserving process shortly after the Big Bang, which could include annihilation of particles in the ultra-hot environment of the early universe. In that case, the dark matter particles created then could still be with us today.

We know that the total amount of dark matter, if it is the correct description for the phenomena described by it, is almost perfectly stable on time scales of the age of the universe, whether or not it actually decays at an infinitesimal rate over tens of billions over years.

But, it could have been produced by annihilations of particles at such high temperatures that those kinds of processes could no longer occur, shortly after the Big Bang when the temperature of the universe was high enough to allow this to happen.

We know that even the most powerful particle collider that mankind has ever known, the Large Hadron Collider (LHC) in Switzerland, does not create any measurable number of dark matter particles in the extreme high energy collisions in an extremely high temperature environment that it creates. So, if there is a process that can create dark matter at high temperatures, the threshold temperature to do so had to be much higher than the temperature at the LHC in its highest energy particle collisions.

But, it certainly isn't unprecedented in physics for there to be "phase changes" in which physical systems suddenly behave very differently at threshold temperatures.

For example, at a certain temperature, particles like protons and neutrons fall apart and instead dissolve into something called "quark gluon plasma". In the time interval of 10⁻¹⁰–10⁻⁶ s after the Big Bang, matter existed only in the form of a quark–gluon plasma. The temperature of the universe at the end of this time period is about the same as the highest temperatures that has ever been reproduced in experiments on Earth.

It could be that there are new laws of physics that could produce dark matter than we don't know about because those laws of physics only become noticeable at temperatures far greater than we can reproduce in any particle collider or observable "natural experiment."

But if this is the case, all of the dark matter in the universe today would have had to have been created in much less than the first millionth of a second after the Big Bang.

A hypothetical kind of dark matter that is formed by high energy processes in the early universe and then ceases to be created as the universe cools down is called "thermal freeze out" dark matter.

This kind of dark matter is still one of the most popular hypotheses about the nature of dark matter particles if they exist, and it used to be the predominant hypothesis among astrophysicists. Thermal dark matter is a less popular hypothesis now than it used to be, because since then scientists have come up with lots of other good ideas about what dark matter could be, and these new ideas compete with each other for attention and popularity.

If thermal dark matter is the right scenario, then the average velocity of dark matter particles (i.e. whether they are "hot", "warm", or "cold") is tightly related to the mass of the individual dark matter particles, because a particle's mass determines the temperature at which it "freezes out".

We know from what we observe in the structure of the universe that if dark matter is of the thermal freeze out type, that it must be either "warm" or "cold" dark matter.

If we lived in a universe full of "hot" dark matter (e.g. one with thermal freeze out dark matter particles with masses similar to the masses of neutrinos), the ordinary matter in the universe would be much less clumpy than we observe it to be, and galaxies like ours would not exist.

If thermal dark matter is "warm" this implies that dark matter particles must have a mass of at least about one keV/c², which is at least a thousand times more massive than neutrinos, but something on the order of ten to a hundred times less massive than electrons. Some observational evidence about how ordinary matter in the universe clumps together favors warm dark matter theories slightly over cold dark matter theories.

But there are disputes among astrophysicists over how much of a difference the difference in average velocity between warm dark matter and cold dark matter would really make in what we observe. It takes a massive amount of computing power to simulate the different possibilities, and there are lots of assumptions that go into any simulation whose effects on the outcome aren't always obvious. So, it is hard to know whose opinion on the differences between a universe with warm dark matter and a universe with cold dark matter is right.

If thermal dark matter is "cold" this implies that dark matter particles must have a mass at least on the order of one GeV/c², which is about the same as the mass of a proton or a hydrogen atom, and might been hundreds or thousands of times more massive than that.

If dark matter particles exist and dark matter is not thermal, however, then there must be some process that creates new dark matter particles and destroys them on a regular basis in our current much colder universe at almost exactly identical rates over time. But, if that is the case, the relationship between the mass of dark matter particles and their mean velocity is broken, so we know even less about it.

If dark matter is not thermal, then the dark matter that we see today wasn't all created in the first tiny fraction of a second after the Big Bang and doesn't require ultrahigh temperatures to be created. So, if dark matter is not thermal dark matter, then it probably wasn't created in annihilations involving physical processes that only happen at ultrahigh temperatures in the early universe. Non-thermal dark matter could still be created by annihilations, but in that case, it would have to be in annihilations of particles made out of something that doesn't interact with ordinary matter and can't be made or detected in particle accelerators.

In the non-thermal dark matter hypothesis, lots of the stuff in the universe is made up of stuff we can't detect except through gravity. That non-thermal dark matter stuff lives in its world where it may interact with other kinds of non-thermal dark matter. But the dark matter in the universe almost completely ignores what is going on with the ordinary matter that we see every day in the universe, which also mostly minds its own business and ignores dark matter. This would explain why we don't see it at particle accelerators when we crash particles of ordinary matter into other particles of ordinary matter at extremely high temperatures and energies but don't see any dark matter, and why we don't see it in experiments designed to directly detect interactions between dark matter and ordinary matter. But, while dark matter and ordinary matter would usually just ignore each other, dark matter and ordinary matter would still interact through gravity, at least, because the whole idea of dark matter exists because it seems like those gravitational interactions between dark matter and ordinary matter are happening.