Cosmological constant?

WoolyJumper

First I want to start this by saying I haven't studied any kind of science since my junior cert so sorry if i'm asking a dumb question. I was just watching the documentary Particle fever. In it one scientist introduced the concept cosmological constant. He gave two possible explanations for it, either there was a creator to fine tune the number or we were one universe in a system of multi verses. Towards the end of the documentary there was a particular result of the experiment that would suggest if we were part of a multi verse or not. Now the scientists didn't really want that finding because it would create an end point in physics..they would not be able to discover any more particles. Does that mean the alternative result would suggest there was some kind of creator and that was the result they were hoping for?...or was there something I was missing? In the end the result was somewhere between the two so it didn't show one way or another. But are they really the only two explanations for the cosmological constant? Both kind of seem a bit out there to me.

I should also end by saying I really know nothing about the cosmological constant other than the brief explanation the guy gave and that its an important number for physics and the laws of the universe.

Labarbapostiza

WoolyJumper wrote: »

Does that mean the alternative result would suggest there was some kind of creator and that was the result they were hoping for?...or was there something I was missing? In the end the result was somewhere between the two so it didn't show one way or another. But are they really the only two explanations for the cosmological constant? Both kind of seem a bit out there to me.

You have to be wary of some of these science documentaries. Any mention of God or the possibility of a creator, usually means there are religious people involved in the documentary, and they're adulterating it with their religious beliefs. There are quite a few of these documentaries on line.

The "fine tuning" of the universe is often used as "evidence" for a creator. The universe is not in fact "fine tuned". If the physical constants were slightly different we'd have a slightly different universe.

Multiverses and the cosmological constant, are quite out there, but there is nothing supernatural or anything that indicates the hidden hand of a stone age sky god. Modern physics is just a little "out there" by itself. The cosmological constant is to do with empty space in our universe; it's slowly expanding. It comes from Einstein's general relativity. He regretted putting the constant in his equations, because he considered that it might not exist, that it's zero. Some people did calculations where it was infinity (they weren't calculating properly). What is believed to be the correct calculation, the value for the constant is really really tiny, but it's there, it seems to match astronomical observations.

WoolyJumper

Labarbapostiza wrote: »

You have to be wary of some of these science documentaries. Any mention of God or the possibility of a creator, usually means there are religious people involved in the documentary, and they're adulterating it with their religious beliefs. There are quite a few of these documentaries on line.

The "fine tuning" of the universe is often used as "evidence" for a creator. The universe is not in fact "fine tuned". If the physical constants were slightly different we'd have a slightly different universe.

Multiverses and the cosmological constant, are quite out there, but there is nothing supernatural or anything that indicates the hidden hand of a stone age sky god. Modern physics is just a little "out there" by itself. The cosmological constant is to do with empty space in our universe; it's slowly expanding. It comes from Einstein's general relativity. He regretted putting the constant in his equations, because he considered that it might not exist, that it's zero. Some people did calculations where it was infinity (they weren't calculating properly). What is believed to be the correct calculation, the value for the constant is really really tiny, but it's there, it seems to match astronomical observations.

Thanks for the reply, tbh I think id have to have more knowledge of physics before I could begin to understand what is meant by the cosmological constant. Yeah the argument this guy made (though it was only briefly touched on) was that there could only be two real explanations for this perfect number that supports our kind of universe and therefore life existing and that is either someone fine tuned the number or that there are so many universes all with different numbers that due to probability one with the right number is bound to exist. He seemed to be suggesting that if the number was different, the universe as we know it wouldn't exist and there for life wouldn't exist.

I find it hard to get my head around both ideas tbh, which is strange because I readily accept the theory that the universe is so big, with so many planets that there is bound to be at least one with all the right conditions to support life. But I guess if that is possible then so is the idea of multiple universes. As for there being a creator...even if science did point towards that...it still takes a giant leap to conclude there is some kind of afterlife let alone that the creator is some kind of magic man in the sky who is overly concerned with out behaviour.

Morbert

Towards the end of the documentary there was a particular result of the experiment that would suggest if we were part of a multi verse or not. Now the scientists didn't really want that finding because it would create an end point in physics..they would not be able to discover any more particles.

This doesn't sound right. I'd have to see the documentary to understand the context, but a multiverse wouldn't spell the end of physics.

Multiverse can mean different things. The multiverse in inflationary cosmology, for example, is really just a single universe with distinct, isolated, spatially separated regions. The "Everettian" multiverse of quantum mechanics is an interpretation of quantum states and their evolution. The documentary was probably referring to the former. Either way there is still plenty of physics to explore. E.g. We could look for some theory or model that describes the relationships and dynamics of universes within a multiverse (This is what inflationary cosmologists often do).

I readily accept the theory that the universe is so big, with so many planets that there is bound to be at least one with all the right conditions to support life. But I guess if that is possible then so is the idea of multiple universes.

This is an important point. There is plenty of precedent for "decentralising" our relationship with the universe. The conditions and properties we experience are local. Cosmological models are ultimately empirical descriptions of patterns and structures in the observable universe. They're not philosophical treatise on Leibnizian questions of the nature of reality.

Anonymo

WoolyJumper wrote: »

First I want to start this by saying I haven't studied any kind of science since my junior cert so sorry if i'm asking a dumb question. I was just watching the documentary Particle fever. In it one scientist introduced the concept cosmological constant. He gave two possible explanations for it, either there was a creator to fine tune the number or we were one universe in a system of multi verses. Towards the end of the documentary there was a particular result of the experiment that would suggest if we were part of a multi verse or not. Now the scientists didn't really want that finding because it would create an end point in physics..they would not be able to discover any more particles. Does that mean the alternative result would suggest there was some kind of creator and that was the result they were hoping for?...or was there something I was missing? In the end the result was somewhere between the two so it didn't show one way or another. But are they really the only two explanations for the cosmological constant? Both kind of seem a bit out there to me.

I should also end by saying I really know nothing about the cosmological constant other than the brief explanation the guy gave and that its an important number for physics and the laws of the universe.

The cosmological constant is an energy of the vacuum which exerts an outward pressure acting against gravity. Gravity causes things to collapse, pressure pushes them out. General relativity says that spacetime is curved by the presence of matter. For normal matter (or radiation for that matter) in an expanding universe the effect is to cause the expansion rate to slow down the expansion. The outward pressure of the vacuum energy (cosmological constant) is large enough to cause the rate of expansion to increase. However the vacuum energy is so small that it has taken billions of years for this energy to dominate over that from radiation or matter.

What is puzzling is that the vacuum energy is so small. This is what's referred to as the fine tuning. Suppose it came from a quantum fluctuation - which is what's expected. Back of the envelope calculations say this should be roughly the Planck mass (anything quantum is usually associated with a Planck unit!) to the power of four. This number is $10^{120}$ too large.

How to explain this? (1) Either there is some symmetry which explains it (supersymmetry says the vacuum energy is zero, so that's not quite right but maybe it's part of the explanation).
(2) We could understand that there are many universes allowed within the string theory landscape of universes. There are often quoted to around $10^{500}$ of those (actually it could be infinite). This is the multiverse explanation. In this context we can use what's called an anthropic principle, and basically say "well we know that it's plausible to form a universe with such a small cosmological constant. Too small or too large a cosmological constant would mean humans don't exist, so the fact that we see it just indicates that we must be in a universe with small cosmological constant". In that sense it's not so special.
(3) It's just very fine tuned. Attach pseudo-scientific explanation/divine creator explanation here.

Hope that helps.

Labarbapostiza

Anonymo wrote: »

What is puzzling is that the vacuum energy is so small. This is what's referred to as the fine tuning. Suppose it came from a quantum fluctuation - which is what's expected. Back of the envelope calculations say this should be roughly the Planck mass (anything quantum is usually associated with a Planck unit!) to the power of four. This number is $10^{120}$ too large.

But the figure for the cosmological constant does come from summing quantum fluctuations. And that is fluctuations running forward and backward in time (positive matter runs forward in time, antimatter runs backward in time). When the calculations are done the result is something like +/- 1 x 10^-120. If the real cosmos was - then for as much as that effect the universe would be shrinking. With a + it appears to be expanding, as it is.

It's not a back of a beer mat calculation, or if you wanted to do it on beer mats it would take a lot of beer mats.

The Planck mass/energy quanta is h-bar. That's the granularity of all the matter we notice in our universe, but that little tiny energy in the cosmological constant, its' behaviour is expected to be a kind of decay into empty space.....as in it creates a little more empty space instead of creating particles we might notice. We can notice the cosmological constant through astronomical observations, which see things on an absolutely astronomical scale.

The idea that empty space can create matter, or that matter can create empty space is one of those out-there freaky ideas. Just start thinking about Special Relativity and Lorrentz contractions/expansions (space expands as you recede, reducing the energy density of that space, contracting on your approach, increasing the energy density - but when you're not even there what's there?)

Anonymo

Labarbapostiza wrote: »

But the figure for the cosmological constant does come from summing quantum fluctuations. And that is fluctuations running forward and backward in time (positive matter runs forward in time, antimatter runs backward in time). When the calculations are done the result is something like +/- 1 x 10^-120. If the real cosmos was - then for as much as that effect the universe would be shrinking. With a + it appears to be expanding, as it is.

It's not a back of a beer mat calculation, or if you wanted to do it on beer mats it would take a lot of beer mats.

The calculation is this. The cosmological constant is measured to around (10^-3 eV)^4 [eV meaning electron volt -- a useful unit of energy in high energy physics]. The Planck mass energy h-bar is around 10^28 eV. Dimensionally the cosmological constant is a mass-energy to the fourth power. The logical mass energy to ascribe to it is the Planck mass energy. So we expect it to be (10^28 eV)^4. So the difference is (10^28/10^-3)^4~ 10^124
I think most beer-mats could handle that calculation!!

Labarbapostiza wrote:

The Planck mass/energy quanta is h-bar. That's the granularity of all the matter we notice in our universe, but that little tiny energy in the cosmological constant, its' behaviour is expected to be a kind of decay into empty space.....as in it creates a little more empty space instead of creating particles we might notice. We can notice the cosmological constant through astronomical observations, which see things on an absolutely astronomical scale.

The idea that empty space can create matter, or that matter can create empty space is one of those out-there freaky ideas. Just start thinking about Special Relativity and Lorrentz contractions/expansions (space expands as you recede, reducing the energy density of that space, contracting on your approach, increasing the energy density - but when you're not even there what's there?)

Empty space does not "create matter". The point is that the vacuum is not empty. In it there are positrons and electrons for example constantly popping up and annihilating all the time. At this time the energy levels are too low for them to escape each other before annihilating. However when the universe was much smaller in the seconds after the big bang, the energy levels were hight enough and positrons and electrons could exist separately thereby populating the universe with matter. [This is a very approximate description but not inaccurate]

Your statement that matter creates space I guess is ok since general relativity says that the geometry and dynamics of spacetime is determined by the energy content.

Alcoheda

I watched that documentary and while I didn't get the impression that they were trying to suggest a creator, I did feel that they glossed over a lot of detail.
These documentaries try to appeal to a very wide audience so they're never a good place to look for rigorous explanation.

I'm only a hobbyist myself and would not be as knowledgable as the other posters on here but I would like to recommend this man.

https://www.youtube.com/user/DrPhysicsA

This playlist might help you to understand the reasons Einstein began thinking about the cosmological constant.

https://www.youtube.com/playlist?list=PL72DD6CBED89C0A06

The guy covers the British physics curriculum from GCSE (junior cert) to A Level and beyond.

It's handy because you can go back to his GCSE videos if you feel that he's using terms or concepts that you don't understand.

He's a retired physics teacher so he keeps it real.