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ETpro's avatar

Is the total mass and energy of the Universe constant?

Asked by ETpro (34521points) October 19th, 2013

Cosmologists have always just assumed that, due to the laws of thermodynamics, the total energy and mass of the Universe must remain constant. But if there is dark energy and dark mass in empty space, which certainly appears to be the case; and if space is expanding at an exponentially increasing pace; doesn’t that imply that the total mass and energy of the Universe must also be increasing exponentially?

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11 Answers

zenvelo's avatar

No, it does not imply that, it just means the empty spaces get bigger. From what I understand, the emptiness is not all dark matter and energy.

Berserker's avatar

I don’t know a hell of a lot about space, but I think some space dudes before said that there are most likely to many important elements about the universe that we don’t know about, and we would need to know that for sure to know exactly how stuff like mass and energy and expansion work in. Also I’m wondering, has it been totally proven that the universe keeps expending? How do people know that? We don’t even know if space is infinite or not. do we?

BhacSsylan's avatar

Agreed, it does not follow. While we’re decently sure of the existence of dark matter and energy (even if we don’t know what it is), it doesn’t seem capable of breaking laws of thermodynamics. Dark matter is not popping out of empty space, it’s been around since the beginning, that’s part of the way that we know it exists and how much exists. Dark energy we’re admittedly more fuzzy on, but it still doesn’t seem to break the laws of thermodynamics. Now, part of that is it works over such massive timescales it’s hard to measure, but currently it looks like it’s still consistent, if strange.

@Symbeline It’s been proven as much as something can be proven in science, it’s expanding and at an accelerating pace (hence the dark energy issue). Originally noticed by Edwin Hubble (in whose honor the telescope is named after) in 1929 and repeatedly confirmed since.

funkdaddy's avatar

I think if we’re using “universe” to mean the biggest container that everything else fits in, then yes, (my understanding is) the total would be constant even if the form changes.

I don’t think the theory is that it’s expanding at an exponentially increasing pace though, right? It’s just still expanding, and even accelerating, but eventually will stabilize and then collapse again. My understanding is that the shrinking universe of the far future will hold the same amount of mass and energy as the expanding universe does today.

But if we’re talking about “universe” in a theory where we have a whole number of possible universes, then who knows. Maybe they swap galaxies like we swap holiday gifts or change physical parameters between them just to see what happens.

Thinking about that type of scale and lack of definite rules is where my mind just turns to mush.

BhacSsylan's avatar

“It’s just still expanding, and even accelerating, but eventually will stabilize and then collapse again”

This isn’t the current consensus opinion among astrophysicists. That was the consensus theory before Hubble, but since the expansion is accelerating a heat death, when everything simply spreads so far apart and the overall energy of any given region of space is so low that chemistry can no longer occur and everything just slowwwwws down to essentially nothing, seems more likely. Though other things, such as a new big bang, are also possible. Though we wouldn’t be around to realize it.

flutherother's avatar

All science tells us is that we don’t know. It might stay the same, it might be increasing or it might be decreasing. What is the total mass and energy of the Universe anyway? We have no idea because we don’t know how big the Universe is. The total energy might add up to infinity or cancel out to a big fat zero.

funkdaddy's avatar

@BhacSsylan – trying to read on this and not finding a lot beyond the theory

So, there’s a second expansion at work, changing the basic scale of the universe itself and making the empty spaces farther apart. Once something has enough mass for gravity to affect it, it’s drops out of this second expansion, and gravity takes over, along with the initial expansion started by the big bang.

So “the nothing” or probably more accurately, “the soup of the initial universe”? is expanding at it’s own rate, while objects with mass are “moving” away from wherever the center of the universe is as well, but at a slower rate since they’re no longer involved in the faster overall expansion.

So once galaxies run through a number of internal cycles of smaller scale decay, some will condense into huge black holes comprising the entire mass of the galaxy, and then, once those burn out, we’ll be looking at the heat death you mention. (10^100 years, say what?)

I can’t find anything that mentions observations to back this up, and I know that’s common for theories on this scale just due to the timeframes involved, but we at least have some observation to back the “inertial expansion” (not sure what else to call it).

You mentioned Hubble specifically, was there an observation that prompted this theory? I don’t mind reading if you have a link by chance, just not sure what I’m missing.

And just because it’s the internet and everything can sound like arguing, I’m absolutely not saying “I’m right, prove it or your wrong”... just genuinely interested, want to learn more, and appreciate the correction.

BhacSsylan's avatar

Heh, no problem. Admittedly I don’t have a great deal of links handy, most of my knowledge comes from listening to talks and knowing astrophysicists, etc. So I could be wrong, grains of salt, etc. I’m a chemist, not an astrophysicist. Also, lots of this comes from Wiki, full disclosure >.>.

Anyway, last question first, the Hubble comment refers to what’s now known as ‘Hubble’s Law’, which refers to the fact that, essentially, all things in the universe (except those close enough for gravity to overcome this) are speeding away from each other. I misspoke a little, Hubble didn’t directly observe the ever-accelerating universe, that came about later as a result of his initial findings that the universe was expanding.

Now, the accelerating universe is known as calculations of what’s called, rather inaptly at this point, the deceleration parameter ‘q’, which is essentially just a ratio of the change in Hubble’s Constant, which relates to the speed of the expansion. For a long time, it was assumed that q would be positive, which means things are slowing and we’d eventually turn around and end up in a big crunch. Which would actually be a fascinating universe to live in, as the universe’s energy density would increase over time as it crunched back together, leading to some fascinating chemistry. But, alas, detailed measurements of galaxies farther back in time (and this was determined in 1998, i believe) have shown that q is in fact negative, which means that the universe is speeding up its expansion. This was found by, appropriately enough, the Hubble Telescope, which showed via extremely far away supernova that the relative expansion in the distant past was slower than it is now. It was originally assumed that the force of gravity would have slowed the expansion over time. It still could have led to a heat death if gravity could not overcome the inertia imparted by the big bang, but it still would have been slowing by some degree. But, that does not seem to be the case, and instead we’re going faster. Now, what is doing this we still don’t know (again, hence ‘dark’ energy), but it definitely seems to be happening.

Now, the results of this are still admittedly in doubt (we’ll know if when it happens >.>). However, in order for the big crunch hypothesis to still be true, there would have to be the emergence of yet another unknown force sometime in the future which is strong enough to not only oppose the intertia put in by the big bang, but also oppose and overcome the force of dark energy speeding up the expansion. While not technically impossible, it seems highly unlikely to occur at this point, there’d have to be some unforeseen physics operating only at inconceivable length scales to have that suddenly happen and reverse the expansion.

Also, besides wiki some of this comes from space.com: http://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html which may be a good read, though it’s light on the specifics as well.

ETpro's avatar

@zenvelo We now know that empty space—a vacuum—is not empty space at all. It is a seething, boiling cauldron of potentialities. Quantum mechanics tells us that it’s not only possible to get something from nothing, you HAVE to get something from nothing. Virtual particles and anti-particles poof into existence constantly in empty space. And they exist for an incredibly short time before they almost always come together and self annihilate. While they exist, they have mass. When they self annihilate, they release energy. And while each particle pair (particle and antiparticle) have very little mass and their self-destruction releases a small amount of energy, it might seem we could just ignore them. But that would be a HUGE mistake.

Bear in mind that almost everything in the Universe is empty space. It’s not just the open space we see. Even in a very dense atom like lead, if the nucleus were a small spot in the center of a football stadium, the electron shells would be various spheres out in the parking lot where an electron that’s essentially a point particle can be found somewhere in it’s range of probabilities.

Even if we drill down into the nucleus of the lead atom, we discover its protons and neutrons. In the case of heavy elements like lead and uranium, the diameter or the electron cloud is about 23,000 times greater than that of the nucleus. In an Hydrogen atom, the electron potentiality sphere is 145,000 larger than the nucleus. But nuclei are not at all like little marbles. They are made of subatomic particles which, like electrons, appear to be point particles. In other words, this entire Universe is almost entirely empty space.

In fact, as the link above notes, the energy of empty space should be 10^120 greater than the observed level of dark energy. But even that 1/10^120th of the calculated energy of empty space is enough to have space expanding so rapidly that the most distant objects are now moving away from us at apparent speeds faster than the speed of light. While the Big Bang occurred 13.78 billion years ago, the most distant objects are now over 47 billion light years away. The only reason we can see them is that the light we observe left them a little over 13 billion years ago, before the expansion of empty space shifted into overdrive.

mattbrowne's avatar

It seems that dark energy violates the first law of thermodynamics, i.e. the total energy of the universe is increasing.

ETpro's avatar

@mattbrowne Sure seems that way to me too. We are finally getting comfortable with the idea than things on the macro scale behave according to Newtonian physics with the minor improvements Einstein gave us in his Theories of Special and General Relativity. Why would it be so hard to imagine that the Laws of Thermodynamics work in localized closed systems, but not at astronomical scales?

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