5 ms·

The theory is that only 1 billionth of the original matter/antimatter mixture survived as matter. The rest annihilated. But when something annihilates the ener

by ars 3y ago

The theory is that only 1 billionth of the original matter/antimatter mixture survived as matter. The rest annihilated. But when something annihilates the energy doesn't vanish - so where did that energy go??? One person I asked told me it bacame the CMB, but that seems far too weak for the amounts we are talking about.

marginalia_nu 3y ago
If you stretch out the CMB across the volume of the entire universe, it seems plausible it would be pretty faint. That r^-3 term on the energy density is pretty small when r is of order ~100 billion ly or more.
- pfdietz 3y ago
  And there's another factor of r from the redshift of those photons.
scotty79 3y ago
My personal pet theory is that it's in the kinetic energy of relative motion of galaxies. The standard way of looking at things is that galaxies are roughly locally stationary and spacetime between them just inflates. But you could take the opposite look, which someone told me has exactly the same mathematical representation, that galaxies are moving away due to their kinetic energy and sort of drag along the spacetime between them, stretching it. Also I'm not sure about matter-antimatter asymetry. We might be just in a place that locally had a little more matter than antimatter initally. This place might even be the size of the observable universe but we don't know how small part of entire universe is the observable universe. The thesis about matter and matter asymetry comes from the fact that we kinda assume that initially universe was pure energy. But we really can't tell. And everything that doesn't check out in cosmology might be the result of initial conditions being slightly different than the simplest ones we assume.
- gpderetta 3y ago
  > that galaxies are moving away moving away from what? The reason inflation works is that it doesn't require a privileged frame of reference.
  - scotty79 3y ago
    From each other. Bigbang that has a center is perfectly consistent with Hubble law. Imagine that the spacetime is flat, there's no gravity and clumps of matter (galaxies) initially had random velocities. The faster the galaxy was, the further is went till now. What is a bit surprising, is that if you do the math in such universe and compare distances from any galaxy to others and their relative velocities you'll get Hubble law exactly. For every galaxy the distance to any other galaxy is directly proportional to relative velocity between them and they appear to be moving directly away from each other. So even though this big bang had epicenter you can't really tell that it had it or where it was if you can't see the edge. And if our observable universe is small when compared with the size of the entire universe we have a low chance of being near the edge. Try it. You can do it on paper or do a little computer simulation and measure. I did it few years ago. I was quite surprised with the results. Especially with the direction of the relative velocity vectors. They always face directly away from one galaxy to any other.
    - gpderetta 3y ago
      > From each other. Bigbang that has a center is perfectly consistent with Hubble law. So we see all distant galaxies moving radially away us. Are you saying that the big bang happened to be centered, of all the universe, around the Milky Way?
      - scotty79 3y ago
        No. I'm saying that if big bang imparted random velocities on galaxies that were all initially in the same spot (epicenter) then tofay in the reference frame of any galaxy (also Milky Way) it will look like every other galaxy is moving away from it radially with the velocity proportional to the current distance from it. No one will be able to tell where the actual epicenter was if they are too far from the edge to see it. This holds for the universe without gravity, with flat spacetime, Newtonian physics, with three, two or one spatial dimension. Seriously, try to simulate such toy universe. Or just sit down with a piece of paper and consider variant with one spatial dimension. It's primary school math and physics. You'll get Hubble law.
nonameiguess 3y ago
This isn't really a mystery. Mostly annihilating matter/antimatter becomes neutrinos or photons. The neutrinos became the cosmic neutrino background, which we have no means of detecting. The CMB wasn't weak when it first decoupled from matter. You're looking now at something that has been red-shifted by 13 billion years of the expansion of space until it's in microwave wavelengths now. When it was first created, it was energetic enough to ionize all matter in the universe for nearly 400,000 years before it finally decoupled.
- kridsdale3 3y ago
  It must have been wild, at some point in time, to look up from an atmosphere-free body and see that the background color of outer space was blue.
jerf 3y ago
AIUI, what you're missing is that it's an iterative process. Energy comes together and forms a hair more matter than antimatter, and the rest returns to energy. But this wasn't an "exactly one chance" situation; the energy gets a fresh chance to come together and a bit more of it is matter than antimatter, with the rest going back to energy... and so on and so on. If it was perfectly balanced, no amount of iteration would produce matter, but even slight imbalances end up tipping the scale greatly over a lot of iterations. (And of course it was all just a big mess of things, not a clean series of events like my words imply. But that's the idea.)
pfdietz 3y ago
Photons are redshifted as the universe expands, so the total energy in CMBR photons declines with time.

by ars 3y ago

marginalia_nu 3y ago

If you stretch out the CMB across the volume of the entire universe, it seems plausible it would be pretty faint. That r^-3 term on the energy density is pretty small when r is of order ~100 billion ly or more.

pfdietz 3y ago
And there's another factor of r from the redshift of those photons.

scotty79 3y ago

My personal pet theory is that it's in the kinetic energy of relative motion of galaxies. The standard way of looking at things is that galaxies are roughly locally stationary and spacetime between them just inflates. But you could take the opposite look, which someone told me has exactly the same mathematical representation, that galaxies are moving away due to their kinetic energy and sort of drag along the spacetime between them, stretching it. Also I'm not sure about matter-antimatter asymetry. We might be just in a place that locally had a little more matter than antimatter initally. This place might even be the size of the observable universe but we don't know how small part of entire universe is the observable universe. The thesis about matter and matter asymetry comes from the fact that we kinda assume that initially universe was pure energy. But we really can't tell. And everything that doesn't check out in cosmology might be the result of initial conditions being slightly different than the simplest ones we assume.

gpderetta 3y ago
> that galaxies are moving away moving away from what? The reason inflation works is that it doesn't require a privileged frame of reference.
- scotty79 3y ago
  From each other. Bigbang that has a center is perfectly consistent with Hubble law. Imagine that the spacetime is flat, there's no gravity and clumps of matter (galaxies) initially had random velocities. The faster the galaxy was, the further is went till now. What is a bit surprising, is that if you do the math in such universe and compare distances from any galaxy to others and their relative velocities you'll get Hubble law exactly. For every galaxy the distance to any other galaxy is directly proportional to relative velocity between them and they appear to be moving directly away from each other. So even though this big bang had epicenter you can't really tell that it had it or where it was if you can't see the edge. And if our observable universe is small when compared with the size of the entire universe we have a low chance of being near the edge. Try it. You can do it on paper or do a little computer simulation and measure. I did it few years ago. I was quite surprised with the results. Especially with the direction of the relative velocity vectors. They always face directly away from one galaxy to any other.
  - gpderetta 3y ago
    > From each other. Bigbang that has a center is perfectly consistent with Hubble law. So we see all distant galaxies moving radially away us. Are you saying that the big bang happened to be centered, of all the universe, around the Milky Way?
    - scotty79 3y ago
      No. I'm saying that if big bang imparted random velocities on galaxies that were all initially in the same spot (epicenter) then tofay in the reference frame of any galaxy (also Milky Way) it will look like every other galaxy is moving away from it radially with the velocity proportional to the current distance from it. No one will be able to tell where the actual epicenter was if they are too far from the edge to see it. This holds for the universe without gravity, with flat spacetime, Newtonian physics, with three, two or one spatial dimension. Seriously, try to simulate such toy universe. Or just sit down with a piece of paper and consider variant with one spatial dimension. It's primary school math and physics. You'll get Hubble law.

nonameiguess 3y ago

This isn't really a mystery. Mostly annihilating matter/antimatter becomes neutrinos or photons. The neutrinos became the cosmic neutrino background, which we have no means of detecting. The CMB wasn't weak when it first decoupled from matter. You're looking now at something that has been red-shifted by 13 billion years of the expansion of space until it's in microwave wavelengths now. When it was first created, it was energetic enough to ionize all matter in the universe for nearly 400,000 years before it finally decoupled.

kridsdale3 3y ago
It must have been wild, at some point in time, to look up from an atmosphere-free body and see that the background color of outer space was blue.

jerf 3y ago

AIUI, what you're missing is that it's an iterative process. Energy comes together and forms a hair more matter than antimatter, and the rest returns to energy. But this wasn't an "exactly one chance" situation; the energy gets a fresh chance to come together and a bit more of it is matter than antimatter, with the rest going back to energy... and so on and so on. If it was perfectly balanced, no amount of iteration would produce matter, but even slight imbalances end up tipping the scale greatly over a lot of iterations. (And of course it was all just a big mess of things, not a clean series of events like my words imply. But that's the idea.)

pfdietz 3y ago

Photons are redshifted as the universe expands, so the total energy in CMBR photons declines with time.