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Does the universe weigh the same or have as much mass as it had at the time of the big bang?
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Does atomic decay act the same way that matter and antimatter act when they come into contact with each other? The 1/2 life process would fit very nicely with this.
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If there is a possibility that they do act the same what would be the ramifications of this?
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Is their any correlation to the density of matter and how fast they decay?
Ad #1: The sum of mass and energy is the same as it was at the beginning of the universe, i.e., the big bang. Mass and energy are, however, mutually convertible (E = mc² and all that), which means that only the sum of the two is constant, not necessarily the amounts of either.
Actually, matter is conserved and energy is conserved, but that does not imply that the total content of the Universe is constant, and in fact, it has decreased. Conservation of matter and conservation of energy are both local properties: If you have a box, then the change in the amount of energy in the box is equal to the amount of energy flowing through the walls of the box. But the Universe is not a box.
For 2-4, I can’t make sense of what you’re asking. Is radioactive decay like matter-antimatter annihilation in what way?
Mumble mumble branes mumble mumble collisions mumble mumble gravity leaking. (Of course that is all highly speculative, but it would effect the total energy in our universe if true.)
There are three main types of radioactive decay: alpha, beta, and gamma.
Each spits out a particle or particles but leaves behind an atom. This is nothing at all like matter/antimatter annihilation, which would normally lead to the destruction of the original particles and only photons remaining.
I’m pretty sure that no known processes affect radioactive decay. (I’m assuming you mean radioactive decay even though you keep calling it atomic decay.)
I was debating which term to use, radio active decay seemed right but then I thought it might only refer to uranium type atoms.
Yes, according to many physicists. It weighed zero then, and it weighs zero now.
No, they are entirely different in pretty much every conceivable way, other than involving subatomic particles and forces.
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There is a correlation between how many neutrons are in an atom, and how radioactive it is, but it’s not linear in any way. Uranium 238 is gonna stick around for billions of years, but 235 is going to only be chugging along for hundreds of millions. If you look at the elements and their isotopes, there is no direct line that means that more or less neutrons means a longer or shorter half life, it is based on much more complex issues.
Do you mean immediately or eventually? Because for a time there will be neutrinos, electrons, and their antiparticles.
Yes, there may be intermediate products but for this question what really matters is that eventually (which is soon) it all goes boom.
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Mass is not conserved. The earliest stages of the universe certainly had far fewer stable particles lying around.
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Atomic decay arises from the complicated interactions among electromagnetic, weak, and strong forces in a nucleus. Matter/anti-matter annihilation is just a result of the fact than in QFT, any process that isn’t forbidden is compulsory. If you get a particle and its antiparticle together, then all of the various conserved quantities (e.g., charge) cancel out, and there’s nothing forbidding a reaction producing, say, a couple of photons. (You can get different particles from the process at higher energies. Since photons have no mass, there’s no lower threshold for their production as you’d have with massive particles.)
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N/A.
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Not that I’m aware of; for one thing, even solids generally have comparatively huge distances between nuclei. If you’re asking about which isotopes of a given element are stable, that’s a very complicated question that’s more chemistry than physics.
- We only see part of a possibly infinite Universe in which case it is better to ask whether mass density is conserved, but this still throws up all sorts of ambiguities as how should define mass or how we should define the volume which we need to define the density.
Choosing your definitions carefully and throwing in a gravitational energy pseudo-tensor you can have conservation of mass density if you so wish, but I think most cosmologists these days would say that mass (density) is not conserved in a meaningful way.
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I think you’d need to explain a bit more what you means by this.
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See above
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Certainly in the very early dense Universe the stability of many configurations of matter were generally different from what they are today.
People often talk of matter-antimatter annihilation resulting in nothing but photons, but that’s not generally true. An electron and a positron are the simplest case, and they turn into (usually) two photons, true. But a proton and an antiproton, while they can turn into photons (about six of them), they’re much more likely to turn into pions. If those pions are all pi0, then they’ll eventually decay into photons, too, but you’re more likely (about 2/3 of the time) to get one each of pi+, pi0, and pi-. The pi+ will most likely decay into a mu+ and a mu neutrino, and the mu+ will in turn decay into a positron, an electron neutrino, and a mu antineutrino (with corresponding decay chain for the pi-). The resulting electron and positron are likely to end up finding each other (or other equivalent ones), resulting in more photons. The neutrinos and antineutrinos could in principle also find each other and turn into photons, but it’s far more likely, for a number of reasons, that they’ll just zip away never to do anything interesting again for the history of the Universe. Put it all together, and the expected output of a proton-antiproton annihilation is, in the end, mostly neutrinos, both by count of particles and by amount of energy carried away by them.
Hmmm, so do we expect that there is a primordial neutrino flux from the (assumed) early annihilation of early most matter and antimatter? One would assume it has red shifted to very low energy, and is thus essentially undetectable, but the principle might be there.
There is expected to be a cosmic neutrino background, very similar to the cosmic microwave background, and of comparable age and temperature. It would date from approximately 200,000 years after the Big Bang, compared to the CMB’s 350,000 years. Because it’s older than the CMB, it would give us more information, but because it’s not much older, it wouldn’t be very much more information, probably not enough to be worth the effort of detecting it. The cosmic gravitational wave background, on the other hand, would be from much earlier, and while it would be difficult to detect, we do actually have some ideas for how to do it, if we had the funding.
It occurred to me that its absence would raise a few difficult questions. Which perhaps makes looking for it more interesting.
Gosh! Care to expand a little on how?
The basic idea is to take something like LISA, and scale it up a lot, both with more spacecraft, more precise and powerful instruments on each craft, and more distance between them. It’s pretty firmly in dream territory right now, though, given that even LISA itself is unfunded.
Neutrino decoupling occurred much earlier, circa one second (T ~= 1 MeV) after the Big Bang.
Yes, absence would be a big deal. Even a rough measure of the relic neutrino density would be fantastically interesting. It would be a window on stuff happening in the universe prior even to nucleosynthesis.
There is experimental R&D effort happening toward observing the cosmic neutrino background, but a lot of work is still needed. And while observation is already known to be crazy hard*, exactly how hard depends on the actual (and currently unknown) masses of the three neutrinos. It could be many orders of magnitude harder than even the crazy hard optimistic case. Totally worth the hunt, though.
[sub]*using the only currently known viable technique[/sub]
Although the precursor project LISA Pathfinder is well underway (launched in December 2015).