dano718 said:
I am by no means an expert in physics, but I have a question. We have recently found the particle that cause attraction (Bos-Higgs) would it not be reasonable to think the there is a particle that cause repulsion? That would lead to cluster of attraction surrounded by fields of expansion. Would this not fit nicely in the dark energy questions?
What Is Dark Energy?
Dark energy is a hypothesis to explain why astronomy observations seem to indicate that the universe is expanding more rapidly than it is predicted to be expanding under the equations of General Relativity ignoring any contribution from dark energy.
This is measured mostly by how fast supernovas (i.e. the explosive ends of dying stars) of a particular type whose properties are well understood, called "standard candles", are moving away from us given how long ago they occurred. Astronomers are working on new ways to measure it, however, like the gravitational waves created by colliding neutron stars.
The leading explanation of dark energy phenomena is called the "cosmological constant" which is a term in the equations of General Relativity.
The cosmological constant (which is usually described with the Greek letter lambda, i.e., λ, in the equations in which it is used, is the source of the lambda in the LambdaCDM "Standard Model of Cosmology") is equivalent to an extreme low constant mass-energy density distribution of mass-energy everywhere in the observable universe. This constant mass-energy per volume distribution interpretation of the cosmological constant is called "dark energy".
In numerical terms, dark energy is estimated to have
a mass-energy density of about 7 grams smeared perfectly evenly within each cube of space in the universe that is one hundred thousand kilometers by one hundred thousand kilometers by one hundred thousand kilometers. Another way to imagine it is as roughly
the mass-energy of four hydrogen atoms smeared evenly across every cubic centimeter cube in the universe (when the proton that contains most of the mass in a hydrogen atom is normally is about a
femtometer across).
This dark energy density is so low that it is basically impossible to see the effects of it at anything less than intergalactic distances.
In the dark energy hypothesis, the gravitational pull from this thin distribution of energy everywhere in the universe (the vast majority of which is otherwise an almost completely empty vacuum) tends to pull the universe apart without any need for the dark energy itself to have any non-gravitational interactions with ordinary matter.
Thus, in the dark energy hypothesis, the dark energy isn't repulsive. Instead, it exerts an attractive gravitational force just like all other matter and energy, but is otherwise inert and doesn't interact with anything.
There is a serious problem with thinking of dark energy as a subatomic particle. This is that the amount of dark energy in the universe is not constant.
In the dark energy hypothesis, close in time to the Big Bang, dark energy was the source of only a negligible percentage of the mass-energy in the universe. In contrast, now, dark energy is estimated to account for about 70% of the mass-energy in the universe, without any decrease in the aggregate amount of ordinary matter or dark matter in the universe. The total amount of dark energy adds up to such a huge amount, even though there is barely any of it in any one place, because the universe is huge and mostly empty (except for dark energy).
In the dark energy hypothesis, the amount of dark energy per volume of space-time stays constant always and everywhere, but the universe expands into more space-time giving rise to more dark energy.
The dark energy/cosmological constant hypothesis is a decent fit to astronomy observations (although there are some weak tensions between astronomy observations and this model, some of which tend to favor more complicated models with more dark energy in the very early universe than a simple cosmological constant model of dark energy would suggest).
But, observations that we attribute to dark energy are a horrible fit to dark energy being made out of some kind of subatomic particle that is evenly spread out throughout the universe.
This isn't how subatomic particles work. The total amount of mass-energy in the form of subatomic particles in the universe can't be increased in one place without destroying the same amount of matter-energy in the form of subatomic particles somewhere else. But this isn't a good fit to the dark energy phenomena that we see.
Therefore, dark energy phenomena cannot be explained well by a subatomic particle that gives rise to a repulsive force.
The Higgs Field And Cosmological Inflation
Some cosmologists think that there is another phenomena out there that is different than dark matter and different than dark energy called "
cosmological inflation".
To vastly oversimplify, in the cosmological inflation hypothesis, in something close to the very first instant of the universe, the universe expanded for a brief moment, much faster than its expansion now, and this smoothed out the universe.
There are literally hundreds of different variations on this basic cosmological inflation hypothesis that have been proposed, some of which have now been ruled out by astronomy observation. But dozens of variations of the cosmological inflation hypothesis are still consistent with what our telescopes have seen so far.
One of the more popular versions of the cosmological inflation hypothesis, called
Higgs inflation, relates cosmological inflation to the high energy behavior of the Higgs field that is connected to Higgs bosons. An advanced power point presentation made at CERN explaining the idea of Higgs inflation, and its problems, can be found
here.
Higgs inflation is a popular cosmological inflation theory variant because it relies upon the properties of particles we have already discovered and started to understand. It doesn't just make up some new particles or forces from scratch, without any connection to real world scientific experiments about those particles and forces, to solve one set of astronomy observations with no connections to any other scientific problems.
Since the Higgs boson has a mean lifetime of only about 1.56 * 10^-22 seconds, it also makes more sense to use the Higgs boson to explain a hypothetical cosmology phenomena that only lasts for a tiny fraction of a second, than it does to explain something stable like dark energy that appears to last forever without any change in any one place.
The high energy behavior of the Higgs field can be calculated to high precision with only minimal assumptions (given what we know about the mathematics of
how subatomic particles behave differently at different energy scales, and the roughly parts per thousand precision with which we have measured the
Higgs boson mass).
But, this does involve extrapolating the behavior of the Higgs field to energy scales far beyond the energy scales at which we can confirm that our calculations are correct with experiments, using calculations with our current understanding of the Higgs field. So, if there are new laws of physics that are only relevant at high energies, that we don't know about because we haven't done experiments at those very high energies, our Higgs inflation calculations are wrong.
This is concerning because many prominent physicists believe that there probably are new laws of physics that are only relevant at high energies. These physicists believe that the laws of physics that we know and love are probably only "
low energy effective theories" that ignore additional laws of physics that only apply at high energies.
Higgs inflation is just one contender of many dozens of different cosmological inflation theories that are still in the running given current astronomy observations and it has problems of its own.
But if there is any astronomy/cosmological role to be played by the Higgs boson and Higgs field, that place is most likely to be in connection with cosmological inflation, and not in connection with dark energy.
