Are Antiparticles the Key to Understanding the Universe?

[mark!]

Yes, it's the same no matter where you are in the universe. Again, there is no center.

I'm not yet able to wrap my mind around the notion that quasars are the most distant objects (the Universe’s toddler years) in all directions, as seen from the Milky Way, but at the same time this is true for a galaxy that is located somewhere in a random direction near the edge of the observable Universe, in between the Milky Way and those distant quasars. How can they possibly observe the same thing as us? There must be something I'm missing here.

 

[PeterDonis]

How can they possibly observe the same thing as us?

They aren't observing the same quasars that we observe. They are observing our part of the universe as it was billions of years ago. At that time our part of the universe would have looked similar to the part of the universe that we currently observe to have quasars in it.

 

[Grinkle]

How can they possibly observe the same thing as us?

Imagine you are in the middle of the ocean and in a region with no land for many hundreds of miles in any direction, and your view is curtailed by the horizon. You see the ocean as far as you can see in every direction.

Now imagine another observer just over the horizon. Knowing what you know for certain about the ocean, you know for sure that the person just over the horizon sees some of what you see, some of what you cannot see, and that what you cannot see but they can see looks just like what you can see at a large enough scale, probably at a scale of 10x or 100x whatever the average length of the waves are. Don't imagine any approaching storms. ;-)

What you know for certain about the ocean in terms of the "observable ocean" being the same as what is over the horizon is how it is being suggested to you to think of the entire universe vs the observable universe.

 

[phinds]

I'm not yet able to wrap my mind around the notion that quasars are the most distant objects (the Universe’s toddler years) in all directions, as seen from the Milky Way, but at the same time this is true for a galaxy that is located somewhere in a random direction near the edge of the observable Universe, in between the Milky Way and those distant quasars. How can they possibly observe the same thing as us? There must be something I'm missing here.

To state what Peter and grinkle have already said but in slightly different terms, what you are missing is the Cosmological Principle, which states that the universe on large scales is homogeneous and isotropic (plus of course the fact that it at the very least WAY bigger than the Observable Universe)

https://en.wikipedia.org/wiki/Cosmological_principle

This leads to the obvious conclusion that there is no center and things on a large scale look identical no matter where in the universe you are.

Check out the link in my signature.

 

[alantheastronomer]

I'm not yet able to wrap my mind around the notion that quasars are the most distant objects (the Universe’s toddler years) in all directions, as seen from the Milky Way, but at the same time this is true for a galaxy that is located somewhere in a random direction near the edge of the observable Universe, in between the Milky Way and those distant quasars. How can they possibly observe the same thing as us? There must be something I'm missing here.

Quasars don't appear to be permanent; they seem to evolve over time, becoming quiescent galactic nuclei of normal galaxies. This is why there seems to be a dearth of them in the nearby region of the universe. We see quasars as they were tens of billions of years ago; shifting to the point of view of a galaxy located near the edge of the observable universe, you're no longer seeing them as they were tens of billions of years ago, instead you're seeing them as they look in the "present" day - as quiescent galaxies. You now also have a new horizon where you can look tens of billions of light years distant and observe new young quasars as they were tens of billions of years ago!

 

[mark!]

They aren't observing the same quasars that we observe. They are observing our part of the universe as it was billions of years ago. At that time our part of the universe would have looked similar to the part of the universe that we currently observe to have quasars in it.

Does this mean that other galaxies also see these distant quasars in all directions in the same way we do? (Because if they don't, that would imply that we're the center of the Universe, and not them).

Look at this picture I've quickly drawn: if our galaxy is A, and some random galaxy is B (see left image), is B really seeing the Universe's toddler years (quasar distribution) the same way A (us) are doing right now (see right image)?

 

[PeterDonis]

Does this mean that other galaxies also see these distant quasars in all directions in the same way we do?

Yes, but they are seeing those quasars billions of years away from them, and therefore they are seeing things as they were billions of years ago.

In other words, it isn't that our universe has normal galaxies here now, and quasars billions of light-years away now. Our universe has normal galaxies now, and quasars billions of years ago.

 

[CWatters]

It seems highly unlikely, since these particles are created in pairs, so it is hard to see how they could separate on a large scale.

Was it a large scale when they were created?

 

[mark!]

Yes, but they are seeing those quasars billions of years away from them, and therefore they are seeing things as they were billions of years ago.

In other words, it isn't that our universe has normal galaxies here now, and quasars billions of light-years away now. Our universe has normal galaxies now, and quasars billions of years ago.

So, there are no quasars right now? Indeed, there were quasars billions of years ago, but none of them exist right now?

This leads to the obvious conclusion that there is no center and things on a large scale look identical no matter where in the universe you are.

Does this mean that the Milky Way looks like a quasar from the viewpoint of a quasar?

I still don't fully grasp the notion that all these distant quasars (which surround us in all directions, the so called 'toddler years' of the Universe) seem to move away from us with the highest possible speed that a galaxy could move away from any other galaxy. Quasars in the north direction of our Solar System have redshifts that are equal to quasars with equal distance to us in the south direction of our Solar System. How then is it possible that a random galaxy (somewhere between the Milky Way and these quasars, in a random direction) is able to observe the same cloud of distant quasars surrounding that galaxy, with the same quasar-redshifts that we're seeing? It doesn't make sense to me how that random other galaxy could have the same viewpoint towards these quasars as us (probably because I don't understand it correctly).

 

[Justin Hunt]

@Mark you are thinking about this the wrong way. You never see anything in its present state, everything you see is in the past. The fraction of a second it takes for the photons to travel from your computer screen to your eyes and then to be processed means you are seeing your screen how it was a fraction of a second ago. While this isn't significant when we are looking at objects here on Earth, it is very important when observing the universe. When you observe an object millions of light years away, you are seeing what it looked like millions of years ago, not how it is right now at this moment. Big Bang theory has the universe expanding into its current state with everything starting at the same time. the reason we see these Quasars at far distance in all directions is because that many billions of years ago they were very common. When we look at closer objects, they are much less common and we won't see anything. No matter where you are in the the universe, closer objects will be seen closer in time to the present and further away objects will be further back in time. If we are in Galaxy A and you see a Quasar in Galaxy C, someone in Galaxy B, close to galaxy C probably won't see said Quasar because they are seeing Galaxy C much closer to the present then we are.

 

[PeterDonis]

So, there are no quasars right now?

Do you see any in our near neighborhood?

Since as far as we can tell the universe is homogeneous, then anywhere in the universe "right now" looks similar to the part of the universe where we are, right now.

You do realize that when we see quasars billions of light-years away, we are seeing them as they were billions of years ago? So those observations are not telling us what those distant parts of the universe are like "right now"; they are telling us what those distant parts of the universe were like billions of years ago.

Does this mean that the Milky Way looks like a quasar from the viewpoint of a quasar?

No, it means that billions of years ago, in our region of the universe, there wasn't the Milky Way; there was a quasar. In other words, our region of the universe has evolved; it is not the same now as it was billions of years ago.

 

[timmdeeg]

I still don't fully grasp the notion that all these distant quasars (which surround us in all directions, the so called 'toddler years' of the Universe) seem to move away from us with the highest possible speed that a galaxy could move away from any other galaxy.

I strongly recommend to read Phinds's article (see his signature) to clarify this key question. At all times things are moving away from each other in all directions, regardless where you are in the universe. Someone very far away from your position will see other galaxies and other quasars but the phenomenon that from any arbitrary position things are receding holds.

 

[Justin Hunt]

@PeterDonis isn't the question of why our observable universe is made of matter still an open question? my understanding is that some kind of asymmetry is just our best guess at the moment. I believe we discovered asymmetry in the weak force, but it wasn't enough to account for our observable universe being all positive matter. I would imagine this is the main avenue of research mainly because it is something that can actually be tested.

If we knew the matter to antimatter composition of our universe and how large our observable universe is compared to our universe, then we would be able to determine statistically how likely it is for the entire observable universe to be comprised of only one or the other. If the entire universe is dominated by matter, then this would obviously be 100%. But, depending on the composition of the universe, it could be nearly 100% chance as well even with no asymmetry. Unfortunately, it is unlikely we will ever know the composition of the entire universe, which is why focusing on matter/antimatter asymmetries makes much more sense.

I have an idea for how matter and antimatter could have separated. Big Bang theory has the entire universe expanding by many orders of magnitude. Now, if matter and antimatter pairs were being created at tremendous rates, then couldn't pieces of pairs annihilate with other pieces of pairs and allow some random distribution of the matter to antimatter ratios (Brownian motion)? This would cause slight fluctuations in the matter to antimatter distribution that would be magnified as the universe expanded. would it be possible for slight variations such as this to be magnified to the size of the observable universe?

 

[PeterDonis]

isn't the question of why our observable universe is made of matter still an open question?

Yes. I believe I already said that early in this thread.

If we knew the matter to antimatter composition of our universe and how large our observable universe is compared to our universe, then we would be able to determine statistically how likely it is for the entire observable universe to be comprised of only one or the other.

According to our best current model, our entire universe is spatially infinite. Our observable universe is spatially finite, meaning there is no way to compare its volume with the volume of the entire universe. So this method doesn't help.

I have an idea for how matter and antimatter could have separated.

Please review the PF rules on personal speculations.

 

[Justin Hunt]

@PeterDonis Sorry for breaking the rules! I will remove the speculative part and ask it as a question. My understanding of Big bang theory is that the concentration of matter in the universe was due to quantum fluctuation in the early stages (I am talking about the location of galaxies and other structures, most of space is empty). My question is then would any fluctuation in the distribution of matter and antimatter in the early stages of the big bang lead to large areas dominated by matter and antimatter at this point?

 

[PeterDonis]

My understanding of Big bang theory is that the concentration of matter in the universe was due to quantum fluctuation in the early stages

That plus the gradual action of gravity over billions of years. The variation in matter distribution in the universe today is much greater than it was in the early universe, because the small fluctuations that were present then (due to quantum fluctuations, yes, but possibly not quite the way you are imagining--see below) have become greatly magnified by gravitational clumping.

would any fluctuation in the distribution of matter and antimatter in the early stages of the big bang lead to large areas dominated by matter and antimatter at this point?

The original fluctuations weren't in the distribution of matter and antimatter. They were in the inflaton field (the field that caused inflation). Those fluctuations got transferred to the fields we call "matter" and "radiation" (the ones that appear in the Standard Model of particle physics) when inflation ended (this process is called "reheating", which is a bit of a misnomer since there wasn't any previous "heating" or "cooling"). The process of reheating should, according to the Standard Model, have created matter and antimatter in equal quantities, which would have meant that, as the universe cooled, all of the matter and antimatter would have annihilated each other and left only radiation (photons). That would still be true even in the presence of fluctuations.

 

[alantheastronomer]

No, there shouldn't. The photons produced during annihilation have redshifted during the intervening time; their present temperature is the temperature of the CMB, because those photons are the CMB. See below.
No, we shouldn't. Recombination did not produce photons; it just drastically increased the mean free path of photons that already existed.

More precisely, before recombination, photons were constantly being created as electrons and nuclei combined into atoms, and then destroyed as they hit atoms just formed and split them apart again. The net effect was a constant photon number. Recombination simply established that constant photon number as free-traveling photons in a transparent universe, rather than an average of constant creation and destruction in an opaque universe.

While some hydrogen atoms were immediately reionized after recombining, the vast majority of electrons first fell to an excited state before cascading down to the first energy level emitting a lyman alpha photon.This IS what's called recombination. You're right, ordinarily there would be an equilibrium between absorptions and emissions, but as the universe expanded the photons became slightly redshifted enough and the mean free path became long enough that the matter became transparent and decoupling occurred. This is supposed to have happened when the matter was at a temperature of 3000 K. But a blackbody of 3000 K corresponds to an energy of 0.26 eV, while the energy of a lyman alpha photon is roughly 10 eV, so the signal from lyman alpha should dominate any blackbody radiation. But if, as you say, the CMB is due to gamma rays from the era of annihilation and the photon to baryon ratio is a billion to one, then any signal from the era of recombination would be redshifted beyond detection.
However, there's another puzzle involved besides there being an excess of matter over antimatter in the early universe, and that is; if protons and antiprotons, and electrons and positrons were created separately, how is it that the same imbalance occurred for both of them in order to maintain charge neutrality? Is it possible that the first matter to be produced was neutron-antineutron pairs that later decayed into protons, electrons and antineutrinos? Do you think that it's possible that the scant roughly fifteen minutes for a neutron to decay is enough time for the expansion of the universe to separate particles from antiparticles enough for a matter dominated universe?

 

[PeterDonis]

if protons and antiprotons, and electrons and positrons were created separately, how is it that the same imbalance occurred for both of them in order to maintain charge neutrality? Is it possible that the first matter to be produced was neutron-antineutron pairs that later decayed into protons, electrons and antineutrinos?

At the end of inflation, when reheating occurred and pumped a lot of energy into the Standard Model fields, the temperature was much, much too high for protons and neutrons to exist. It was just quarks and leptons. It was only when the temperature dropped low enough that the quarks became confined into nucleons. By that point, electroweak interactions would have equilibrated between quarks and leptons in order to achieve charge neutrality; at least, that's my understanding of the model.

Do you think that it's possible that the scant roughly fifteen minutes for a neutron to decay is enough time for the expansion of the universe to separate particles from antiparticles enough for a matter dominated universe?

That is the half-life for free neutron decay, but as I understand the theory of Big Bang nucleosynthesis, the vast majority of the neutrons were not free; they were bound into nuclei (deuterium, helium, and lithium). Nucleosynthesis was completed within about the first three minutes (hence the title of Weinberg's popular book from the late 1970s).

As for separating particles and antiparticles during that time, I don't know off the top of my head by what factor the universe is believed to have expanded in the first three minutes, but I don't think that's the key point anyway. I think the key point is that the expansion was decelerating (because the universe was radiation dominated), and I think a decelerating expansion won't separate particles and antiparticles the way you are thinking. I think you would need an inflationary expansion to pull particles and antiparticles apart faster than they could annihilate each other, much less to pull them apart to the extent that we now have our entire observable universe filled with matter, as far as we can tell.

 

[hmmm27]

I don't mean to disrupt a serious conversation, but why is the prevailing opinion that matter/anti-matter creation should be even at the beginning ? Not that I don't understand how to flip a coin, but there's an already existing polarity bias, of sorts - behind (towards the big bang point) and ahead (the other way). So maybe something as simple as a particle creation happening while being pushed out of a gravity well makes matter, pushed into makes anti-matter: there's still anti-matter creation, but the bias is clearly towards matter.

 

[PeterDonis]

why is the prevailing opinion that matter/anti-matter creation should be even at the beginning ?

To the extent that this is a prevailing opinion (I'm not sure to what extent that actually is), I think it's because we have no reason, based on our best current physical theories, to expect that the "reheating" process at the end of inflation, that transferred the energy density of the "false vacuum" state of the inflaton field to the Standard Model fields, would have had any bias towards matter; we would expect it to excite matter and antimatter Standard Model fields equally.

there's an already existing polarity bias, of sorts - behind (towards the big bang point) and ahead (the other way)

This is just another way of saying that the big bang is to the past. How is that a "polarity bias"?

something as simple as a particle creation happening while being pushed out of a gravity well makes matter, pushed into makes anti-matter

The big bang and the universe's evolution since then was not a process of anything being "pushed out of a gravity well".

Also, please review the PF rules on personal speculation.

 

[hmmm27]

The big bang and the universe's evolution since then was not a process of anything being "pushed out of a gravity well"

.

Ah, right. I think I'll pass on trying to argue that antimatter is created backwards in time.

 

[Justin Hunt]

Do Cosmologists consider that there could have been exotic particles during the extreme conditions of the big bang? Super symmetry predicts larger particles, but we have been unable to create any of them in our particle accelerators so far. If these particles due exist at the higher energy levels, wouldn't the early universe been dominated by them or has the LHC ruled out this possibility (not sure if the energy level at the LHC is comparable to the energy level of the BB when particles were being created)?

 

[diogenesNY]

I recall a description in the book _Cauldrons in the Cosmos_
http://www.worldcat.org/title/cauld...physics/oclc/4435817210&referer=brief_results

that there was a speculation of highly massive exotic particles that would form and then rapidly decay during a period of unimaginably high energy levels in the _very_ early universe - way higher than we could ever conceivably get with our current (or foreseeablely future) apparatus. This was a 1988 book, however, and this content may well be superseded by current research. Of note, there is a 2005 (revised?) edition. Not sure what the differences or possible revisions are.

diogenesNY

 

[sadovnik]

In my opinion ''Antiparticles'' are Dirac's negative
virtual particles ( -E=Mc^2) and ''Cosmology''
is first of all Dirac's ''vacuum sea'' with parameter: T=0K
===

 

[PeterDonis]

In my opinion ''Antiparticles'' are Dirac's negative
virtual particles ( -E=Mc^2) and ''Cosmology''
is first of all Dirac's ''vacuum sea'' with parameter: T=0K

Your opinion has been known to be wrong for decades now. Dirac's speculation was an interesting early one but the model was fairly quickly found not to work; one key reason why is that it could not explain why bosons have antiparticles.