Can Matter be Created or Destroyed?

[Alex K]

My guess is:

Matter can be created, and it was created during the "Big Bang." I also believe that a reversal of the process, in theory, would be an example of matter being destroyed.

You are talking about the dreaded Gnab Gib here, right...

Whether that is possible in practice perhaps depends on whether the Big Crunch will ever happen. According to Lawrence Krauss it will not, the Universe will keep expanding forever and ever.

According to almost everyone else as well. It's not so much about Lawrence Krauss' opinion, he simply recounts the current scientific consensus here. The crucial issue is about the nature of Dark Energy. If the observed Dark Energy simply takes the form of Einstein's cosmological constant, it always remains the same, as the term "constant" implies. If it remains the same in magnitude, forever it will dominate our destiny - as everything else gets diluted down by the expansion, the cosmo constant prevails unchanged, driving our universe towards eternal exponential expansion. Noone can currently know (for lack of empirical evidence) whether Dark Energy truly is this simplest of all versions or something more complicated, but Occam's razor would suggest that if there is such a trivially simple explanation for the data, we should consider it likely.

ou
So I would say I reckon matter can be created, but not destroyed - assuming Lawrence Krauss is right.

If you like you should read an article on inflation and reheating, to get an idea how matter might have been created from a different form of energy.

Energy however, I believe is eternal. Something must have always existed because it doesn't make sense for "nothing" to exist.

How do you define energy?

It is possible for "empty space" to exist, but that is actually something, just barely. It exists as something at least on the subatomic level. And that is where the title of the book "A Universe From Nothing" by Lawrence Kraus is a misnomer (It should really be called "A Universe From "Empty space"  Which Is Almost Nothing But Actually Just Barely Something At least On The Subatomic Level." - but that wouldn't be a very catchy title now would it? ). Although the science itself I am sure is very accurate.

Yes, I think the name is unfortunate, but if you want to sell, you need something catchy, and this stuff is something publishers love.

Energy cannot be created or destroyed. Matter can be created, and may or may not be able to be destroyed.

Why the distinction between matter and energy here? When you say matter cannot be destroyed, do you mean baryonic matter remains because of baryon number conservation?