Fight my ignorance here, Dopers.
As I understand it, current thought says that the Big Bang created almost equal amounts of matter and anti-matter, with matter slightly predominating. Matter & anti-matter proceeded to annihilate each other, leaving us with the universe we see today. But when matter and anti-matter annihilate, they produce energy, so what happened to the energy? Did it form new matter & anti-matter?
Your ignorance is well-placed unfortunately as nobody really knows the answer.
The symmetry between matter and antimatter is very strong and how exactly it could be that the observable Universe there is a great asymmetry between the abundance of the two is a great mystery. However, it is known though that the symmetry isn’t absolute and there are some processes that have been observed that lead to small violations of this symmetry and it is thought that such a violation could’ve occurred in the early Universe leaving matter to predominate.
The thing is though, whilst highly plausible, this still amounts to mostly speculation and there’s little concrete because we don’t know that much about the details of the physics of the early Universe. The fact that this may suggest in the early Universe a lot of the created matter and antimatter would’ve annihilated, which presumably would leave behind a lot of energetic radiation (any antimatter produced by annihilation would’ve been annihilated itself) is not that much of a problem, at least at first glance, as the early Universe was dominated by energetic radiation for the first few thousand years of its existence, but most of this energy has now been ‘lost’ due to red-shifting due to expansion.
if you’re interested in intro cosmology and general science, check out BBC documentaries starring Jim Al-Khalili, a British cosmologist, on youtube or the other major video sites.
You didn’t have any matter in the universe until things “cooled down” a bit to allow for it. Before, that, things were too hot/energetic to even support matter.
If we accept the current theory that the universe created a ratio like 1.01/1.00 matter/antimatter, then this annhilation would briefly look like a rerversible reaction at equilibrium. (i.e. energy <–> matter/anti-matter) until the energy side of the equation dissipates sufficiently that we stop making new matter. At that point we’re stuck with matter/antimatter -> energy until we run out of antimatter and get left with the 0.01 units of excess matter. As I understand it, all of this happened in just seconds according to the latest theories, so it was very short-lived.
So… where do we see that energy? According to the theory, some of it leaked off the leading edge of the universe, but most of it continued to be absorbed and re-emitted by the leftover matter in the early universe. It’s not until hundreds of thousands of years pass that the light is not routinely absorbed, and that’s what we see as the cosmic microwave background radiation. (Which, remember, is only seen as microwaves now because of red-shifting.)
There is no “leading edge”, nor any other sort of edge. The stuff that flew free is still in the Universe, and we see some of it just now reaching us.
Doesn’t the creation of larger elements tend to be endothermic ?
That is, the 1% imbalance lead to the cycle of matter antimatter anihilation ending ,as the energy from the anti-matter ended up in heavier matter ?
It does take energy, but the vast majority of the heavy elements weren’t made in the early universe, but had to wait for stars to form, grow old and die. Really heavy elements needed to wait for supernovae, or possibly neutron stars to start colliding. Whilst there is probably some trace amount of heavy stuff from the early times, it is essentially undetectable.
Of course there remains the question of the genesis of dark matter. But given no-one knows what it is, the relationship of dark matter to the anti-matter problem is a question that we don’t even know how to usefully pose, let alone answer.
Yeah, that was a bad way to say it.
At the time we see the CMB, the universe was just getting to a point where light could move around without being immediately absorbed by hot matter, which is why we can see things more recently than that and why we can’t see “through” the CMB.
Since energy moves faster than matter, there had to be some photons that escaped being absorbed - not so much the leading edge of the universe itself, but from the leading edge of the matter in the universe. We just aren’t seeing those because Earth hails from inside all that matter and any photons that were heading our direction were absorbed.
I say again, there is no leading edge. The Universe is and was everywhere, and the matter in the Universe is and was everywhere.
Well, if a photon moves faster than a proton, then there should be a place where you have photons and not any protons, am I correct in that?
but there are protons everywhere in the universe, so there is no boundary after which there are only photons
There are photons and protons everywhere in the Universe. The fact that photons are faster just means that, at any given point, those protons have been in that vicinity for longer.
I guess I’m going to have to think about that for a while…
To add a bit…
In the picture usually discussed, the generation of the excess of matter over antimatter does not happen directly from the big bang but rather soon after. This would be very soon after, perhaps 10[sup]-25[/sup] seconds after, give or take 10 orders of magnitude. Very heavy particles and antiparticles (either some specific single species or perhaps multiple ones) would decay into other, lighter particles, but at different rates depending on if the parent were a particle or an antiparticle. If the expansion and cooling of the universe were happening rapidly enough such that those decays couldn’t just undo themselves fast enough, then the asymmetry in the daughter particles would stick around.
We don’t know what these decaying particles would be, but there are a lot of not-too-crazy ideas, and several aspects of the Standard Model of particle physics suggest that the existence of particles with such high masses (say, over a trillion times heavier than the proton) would make a lot of sense for other reasons.
In any case, one the asymmetry is baked in (and in this picture it’s more like a part-per-ten-billion asymmetry), the particles and antiparticles would annihilate. The annihilation products (which eventually would just be photons but earlier would include other particles) would bounce around the soup of the universe and sometimes, as you suggest, convert back into particle/antiparticle pairs. But as the universe cooled and expanded further, the energy available to individual photons became too low to create these particle/antiparticle pairs, stopping this process from happening in bulk. This transition (or “freeze out”) would happen a few seconds after the big bang.
The photons would continue to participate in other processes that hadn’t frozen out yet, notably mundane electromagnetic scattering off the zillions of charged particles everywhere. This would continue up to the time when neutral hydrogen could form, about 380,000 years after the big bang. The last photons to scatter at that time constitute the (now heavily redshifted) cosmic microwave background radiation.
All the matter in the Universe was formed in the first seconds of the big bang. After that the universe is too cold, it requires a temperature of about 6 billion degrees just to form the lightest particles, electrons and anti electrons.
When the temperature is no longer hot enough for energy to become matter, then the matter that is in existence at that time remains as matter and the energy that is in existence at that time like EM radiation for example, remains as EM radiation. What happens to it you ask? Nothing, the photons just keep on flying through space and have been doing so for 13.7 billion years, as the universe expands they get cooler, currently that are raining down on us with a temperature of about 2.7K (that’s 2.7 degrees about absolute zero) this is what is known as the CMBR cosmic microwave background radiation.
An old but excellent book that goes into this in fine detail is The First Three Minutes, by Steven Weinberg.
Escape to where? Because everywhere in the Universe is the centre of the Universe.
I think this is a misleading thing to say on it’s own. Better would be that there is no centre of the universe, because it is infinite.
Dracoi, to clarify what others have been alluding to, the universe is generally assumed to be infinite. If it is infinite now, then it must always have been infinite as there is no way to transition from a finite state to an infinite state.
When you hear statements like “The universe was compressed to the size of a pin head shortly after the big bang”, what they mean is The **visible **universe was compressed to the size of a pin head shortly after the big bang"
As Chronos was saying, there is no edge nor has there ever been because it has always been infinite.
If you imagine a box enclosing a region of the Universe that expands with the Universe then radiation does leave by the sides of the box. However it’s clear from homogeneity and isotropy, that there must be the same amount going one way across a boundary of the box as is going another way, so the net energy loss to ‘escape’ for any comoving region (that is a region that expands with the Universe) is zero.
Once the Universe had settled down and the production of matter and radiation is negligible, as the it expands the total energy in any comoving region due to radiation decreases due to cosmic redshifting, but the total amount of energy due to the mass of electrons, quarks, etc (i.e. matter) stays constant. In addition the amount of dark energy always increases in a comoving region (if it is described by a cosmological constant that is because it is constant for a region of constant proper volume, whereas a comoving region has an expanding proper volume).
This means in an expanding Universe which contains matter and radiation and where there is not a significant amount of conversion between the two, the proportion between the percentage of total energy due to matter to the percentage of total energy due to radiation always increases. Similarly if there is dark energy also present, the proportion between the percentage of total energy due to dark energy to the percentage of total energy due to matter always increases. Which is why after the very early era(s) the Universe is often divided into the radiation-dominated era, the matter-dominated era and the dark energy-dominated era.
It can be finite too and still have no boundaries. There are certain observer-specific boundaries that exist in various models, like the boundary of the observable Universe, but nothing can ever escape the observable Universe by definition.