How can the cosmos be eternal?

[swansont]

1 hour ago, Moreno said:

To my knowledge energy was never isolated in a pure form by any scientists.

This should not be a surprise, as energy is not a substance.

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According to modern generally accepted views energy is just a varieties of a matter movement forms and as such it cannot exist in a completely isolated form.

Motion implies kinetic energy, or if it's vibrations or motion of an ensemble of particles, then you have thermal energy (temperature). Mass is a form of energy, too.  

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Also there is a potential energy as well, it cannot exist separately from the matter. When matter and antimatter annihilate - they create gamma photons which are just another kind of matter.

Photons, however, are not matter. Matter is comprised of fundamental fermions, and photons are bosons.

 

Comparing matter to energy was incorrect. Matter is not converted to energy and energy is not converted to matter. Matter is approximately conserved; you form matter and antimatter, such that the fermion number remains constant, but this is known to be violated on occasion (CP violation). Soon after the big bang there was another violation that resulted in us having more matter than antimatter; that was what I referred to earlier about not having conservation of matter.

Mass can be converted to tother forms of energy, and vice-versa, because mass is a form of energy. Matter has mass, but it is incorrect to say matter is mass.

[Moreno]

14 minutes ago, swansont said:

Photons, however, are not matter. Matter is comprised of fundamental fermions, and photons are bosons.

This is really strange. In some countries any kind of physical fields (such as EM, gravitational) and bosons are regarded as a kinds of matter. I see no reasons to think of photons as not kind of a matter. If not, than what is it? There exist matter conservation law. If annihilaiting matter converts to photons, then it means matter disappeared and matter conservation law was violated?

Edited May 2, 2020 by Moreno

[Strange]

1 hour ago, Moreno said:

To my knowledge energy was never isolated in a pure form by any scientists. According to modern generally accepted views energy is just a varieties of a matter movement forms and as such it cannot exist in a completely isolated form. Also there is a potential energy as well, it cannot exist separately from the matter. When matter and antimatter annihilate - they create gamma photons which are just another kind of matter.

Photons are not matter, by any reasonable definition.

Matter is usually defined to be something with mass and that occupies some amount of space; in other words, fermions (quarks, protons, electrons, etc)

Photons are (a) massless and (b) bosons, which means they do not require their own volume of space. You can put 1 or a million bosons in the same place (which you can't do with fermions).

Energy is a property. But it is a popper of fermions (matter particles) and bosons (such as photons). Juts because photons have energy does not make them matter.

3 minutes ago, Moreno said:

In some countries any kind of physical fields (such as EM, gravitational) and bosons are regarded as a kinds of matter.

Do you mean "in some languages"? Can you give an example. 

But that isn't really relevant. As far as physics s concerned, they are not forms of matter.

4 minutes ago, Moreno said:

There exist matter conservation law.

There is no matter conservation law. There is a mass-energy conservation law (because was and energy are equivalent). Although it does not always apply.

5 minutes ago, Moreno said:

If annihilaiting matter converts to photons, then it means matter disappeared and matter conservation law was violated?

The total energy (or mass equivalent) is the same before and after. 

[swansont]

1 hour ago, Moreno said:

This is really strange. In some countries any kind of physical fields (such as EM, gravitational) and bosons are regarded as a kinds of matter. I see no reasons to think of photons as not kind of a matter. If not, than what is it? There exist matter conservation law.

Some countries? That’s generally not how science is divided up.

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If annihilaiting matter converts to photons, then it means matter disappeared and matter conservation law was violated?

It depends on how you are approaching this. You can look at it as the category of matter, which contains matter and antimatter and in which case there is no conservation whatsoever.

Or you can use e.g. lepton number and say that there’s no net matter when you create a matter-antimatter pair (e.g. lepton number of 1 and -1. Net is zero) In which case it’s mostly conserved, but there are known CP violations.

In either case, matter is not conserved.

(if you insist that photons are matter then conservation of matter fails spectacularly. Photon number is not conserved)

[Moreno]

3 hours ago, Strange said:

Photons are (a) massless

I thought photons have no mass only in the state of rest, hypothetically. But could they practically exist in the state of rest? Probably not. If they are neither matter or pure energy then what are they? It is not known exactly whether neutrino does have any mass. If not, does it mean neutrino is not a matter? Why matter suppose to have mass? I though that according to widespread philosophical definition matter is at least: "everything that exist independently of our perception/imagination and that could be perceived by any means of our perception". Though some kinds of matter, possibly, will never be detected or perceived by humans. As you see there is nothing about the mass in the state of rest. Photons cannot leave black holes and attracted by stars. Therefore they suppose to have mass in the practical sense.

Edited May 2, 2020 by Moreno

[MigL]

Photons don't have mass, they have momentum.
And are incapable of any speed other than c .
A neutrino has ( very small ) mass, and is a fermion ( obeys Fermi-Dirac statistics ), while a photon is a boson ( obeys Bose-Einstein statistics ). There are, however, bosons that do have mass ( W and Z bosons involved with the weak nuclear force which governs neutrino interactions, for one ).
That which gravitates is mass energy, and either will gravitationally interact. The property of energy will just as readily interact gravitationally as the property of mass, in fact J A Wheeler hypothesized non-singular collapsed EM waves ( photons ), and labelled them geons; they are perfectly compatible with GR.

Why do you use a definition of matter which is dependent on the human experience ( philosophical ? ) ???
Matter is simply an aggregate of elemental building blocks called fermions, such as electrons, muons, quarks and their antiparticles.
( neutrinos are fermions, but interact so weakly, they don't 'aggregate' at all )

[Sensei]

9 hours ago, Moreno said:

This is really strange. In some countries any kind of physical fields (such as EM, gravitational) and bosons are regarded as a kinds of matter. I see no reasons to think of photons as not kind of a matter. If not, than what is it? There exist matter conservation law. If annihilaiting matter converts to photons, then it means matter disappeared and matter conservation law was violated?

Photons are particles.

Matter are particles too. Just different kind. Protons, neutrons, electrons mostly.

In the matter conservation law you count the number of Baryons and Leptons (and charges) on the left and right side of the equation and they must match. It is used to properly balance chemical equation, prior and after chemical reaction.

The number of Baryons (protons and neutrons together) is almost matching Dalton unit:

https://en.wikipedia.org/wiki/Dalton_(unit)

e.g. average mass of Carbon is 12.011 u. Baryon number of Carbon C-12 is 12. 6 protons + 6 neutrons. These 0.11 u difference is caused by presence of very little amount of Carbon C-13 and minuscule amount of Carbon C-14.

9 hours ago, Moreno said:

. If annihilating matter converts to photons, then it means matter disappeared and matter conservation law was violated?

Photon has Lepton, Baryon and charge numbers equal 0.

Electron and positron have Baryon number equal 0.

Electron has Lepton number +1. Positron has Lepton number -1.

Electron has charge -1. Positron has charge +1.

Prior annihilation we have electron and positron with leptons +1-1 and charges -1+1. After annihilation we have two gamma photons with the all 0.

 

Edited May 3, 2020 by Sensei

[Strange]

10 hours ago, Moreno said:

I thought photons have no mass only in the state of rest, hypothetically. But could they practically exist in the state of rest? Probably not. If they are neither matter or pure energy then what are they?

There is no such thing as "pure energy".So you are creating a false categorisation between "matter" and "something that doesn't exist".

Photons are quanta of electromagnetic radiation.

10 hours ago, Moreno said:

It is not known exactly whether neutrino does have any mass. If not, does it mean neutrino is not a matter? Why matter suppose to have mass? 

It is known. They do.

The concept of "matter" is not precisely defined. You could say that all fermions are "matter". In which case neutrinos would be. Even though they don't exist in anything that we would normally call "matter" (tables, dogs, etc)

Or you could say that only the particles that make up what we consider to be material objects (electrons, protons, neutrons and maybe quarks) are "matter".

10 hours ago, Moreno said:

Why matter suppose to have mass?

Just because everything material has mass, so that is how we define it.

10 hours ago, Moreno said:

I though that according to widespread philosophical definition matter is at least: "everything that exist independently of our perception/imagination and that could be perceived by any means of our perception".

I suppose that is yet another definition. Not one that is very consistent with physics though. Probably more useful when discussing philosophical ideas like materialism vs idealism.

10 hours ago, Moreno said:

Photons cannot leave black holes and attracted by stars. Therefore they suppose to have mass in the practical sense.

Nope.