Percentage of known energy in the Universe

[mister i]

TL;DR

It is said that the universe is made up of approximately 4.9% ordinary matter, 26.8% dark matter and 69.3% dark energy. Why isn't ordinary energy included in this "pie"?

It is said that the universe is made up of approximately 4.9% ordinary matter, 26.8% dark matter and 69.3% dark energy. Why isn't ordinary energy included in this "pie"? I suppose it is included within ordinary matter, but could it be calculated what % are particles with mass and what % is pure known energy?

 

[Ibix]

"Pure energy" is a science fiction concept, not a physics one.

The mass of composite particles is not the same as the sum of the masses of their constituent particles, it is true. But you can't divide that into "particles" and "energy" in any meaningful way because mass is not an additive quantity.

 

[PeterDonis]

Why isn't ordinary energy included in this "pie"? I suppose it is included within ordinary matter, but could it be calculated what % are particles with mass and what % is pure known energy?

What do you mean by "ordinary energy"? What do you mean by "pure known energy"?

If you mean radiation, that is a tiny fraction of a percent of the total and is not usually included in such breakdowns for that reason. But neither "ordinary energy" nor "pure known energy" are good descriptions of radiation.

 

[mister i]

My knowledge of physics is very limited, for example I don't know if kinetic energy could have an equivalence with matter through the formula $m=E/c^2$. If it does, then my common sense tells me that it must be very large since there are billions of billions of stars moving at high speeds in the universe.

 

[Ibix]

Kinetic energy can be a contribution to mass when there is kinetic energy in the center of mass rest frame. As a fraction of total energy, it is $1-\sqrt{1-v^2/c^2}$, which is approximately $v^2/2c^2$. For typical speeds of astronomical objects it's utterly negligible (sixth decimal place at least).

 

[Orodruin]

common sense

What people refer to as “common sense” generally provides very poor guidance to the physics of extreme objects (such as the entire universe). It is developed from everyday experience and we have very little everyday experience with extreme objects. There is no a priori reason to believe it should be possible to extrapolate.

 

[ohwilleke]

TL;DR Summary: It is said that the universe is made up of approximately 4.9% ordinary matter, 26.8% dark matter and 69.3% dark energy. Why isn't ordinary energy included in this "pie"?

It is said that the universe is made up of approximately 4.9% ordinary matter, 26.8% dark matter and 69.3% dark energy. Why isn't ordinary energy included in this "pie"? I suppose it is included within ordinary matter, but could it be calculated what % are particles with mass and what % is pure known energy?

As others have noted, "pure energy" isn't a thing.

The ordinary matter category is predominantly the mass of atoms which is 98-99% strong force binding energy and 1-2% quark and electron mass. Strong force binding energy is subsumed in the ordinary matter figure. There is a tiny percentage which represents neutrinos, aggregate kinetic energy, and electroweak sources of mass-energy such as molecular binding energy, photons traveling at any given moment from one place to another and the ephemeral "on shell" weak force carrier bosons that exist at any given moment, all of which would usually be included in the ordinary matter category. All of these sources of "ordinary matter" mass combined are smaller than the combined uncertainty in the dark matter and dark energy category amounts. The last time I looked, the uncertainty in the dark energy category was about ± 2% of the total combined amount in all three categories.

The biggest quantitative theoretical uncertainty in the ordinary matter category is probably the differences between plausible definitions of ordinary mass arising from the difference between the sum of the masses of individual objects in gravitationally bound systems and the mass of a gravitationally bound system as a whole, due to general relativity. Implicitly, due to the way the total ordinary mass is calculated, I believe that the later definition is used, but I'm not deeply immersed in how that is calculated.

Dark energy is calculated as a function of the value of the cosmological constant and the volume of the observable universe. There are several different ways that aggregate dark matter mass is inferred (which more or less converge on the same value).

 

[PeterDonis]

the difference between the sum of the masses of individual objects in gravitationally bound systems and the mass of a gravitationally bound system as a whole, due to general relativity. Implicitly, due to the way the total ordinary mass is calculated, I believe that the later definition is used

I believe you are correct, at least to the extent that the difference is large enough to matter.

 

[phinds]

My knowledge of physics is very limited, for example I don't know if kinetic energy could have an equivalence with matter through the formula $m=E/c^2$. If it does, then my common sense tells me that it must be very large since there are billions of billions of stars moving at high speeds in the universe.

Kinetic energy is relative, not absolute. I you get hit by a ball that is speeding towards, you, it hurts because the ball's kinetic energy, relative to you, pushed the ball against you. If, on the other had, you are on a flat car that is going at the same speed as the ball, then the ball won't even catch up with you, and it it did it would just fall directly to the floor of the flatcar.

What would you use as the reference point for all those billions of stars?

 

[jbriggs444]

Kinetic energy is relative, not absolute. I you get hit by a ball that is speeding towards, you, it hurts because the ball's kinetic energy, relative to you, pushed the ball against you.

In a flat space time the internal kinetic energy of a system is an invariant. As you point out, you get hurt by a ball that is speeding toward you. The hurt is the same (invariant) regardless of whether you are moving toward the ball or the ball is moving toward you.

What would you use as the reference point for all those billions of stars?

All of the other stars.

However, on a cosmological scale in an expanding universe, relative velocity is a slippery concept. The kinetic energy of relative motion is slippery as well. If two objects are outside of each other's cosmological horizons then their relative velocity or relative kinetic energy are both meaningless.