During the first moments of the big bang, nuclear fusion reactions made few heavy elements because:?

Question

-no nuclei heavier than helium could form since there werent any electrons formed
-no stable nuclei exist with masses of 5 or 8 hydrogen masses
- the temperature and density were too low
-the helium nucleus is unstable
- all heavy nuclei are unstable

Answer 1

What makes this question hard is what is meant by "the first moments." We advance to the nuclear epoch where hydrogen and helium can exist. But it was still too hot for atoms to form. Just the nucleii. Electrons were there, but not bound to orbits around nucleii.

Helium is a stable nucleus. That's what alpha particles are. The temperatures and densities were not too low. They were much higher than in any star, today, but once again, how long into the big bang are we talking about?

I would have to go with the unstable heavy nucleii. Since electrons had not formed into atomic orbitals yet, the larger nucleii would not bind together.

Answer 2

At the "beginning" of the expansion as we perceive it (mistakenly called the "Big Bang"), there was no matter. Only pure energy. The energy was so dense (= the temperature was so high) that even the forces could not exist. As the universe expanded, it cooled. As the temperature went down, "stuff" was able to condense out of the pure energy. This is not a problem as long as any mass created from the energy follows the famous equation: E = m c^2 At first, only elementary quarks. As the energy density (a.k.a. temperature) diminished, some quarks managed to stick together two-by-two: the "vector bosons" were created -- these are the exchange particles responsible for the nuclear forces (strong and weak). At first, they are all the same strenght (in fact, you could not tell one from the other -- they were "unified"). Then quarks were able to stick together in groups of three, forming "hadrons" (meaning heavy particles), mostly neutrons at first. neutrons are unstable when left to themselves: they break down and form mostly protons (positively charged hadrons -- still three quarks), electrons (an elementary particle) and an anti-neutrino (an elementary anti-particle). A proton and an electron = a hydrogen atom. However, it is still too hot for the electrons to stay in orbit around the protons (the high energy photons keep knocking them off). The protons and neutrons are being pushed around so fast by the energy that they collide and fuse together, to form helium and a few heavier atoms (lithium, beryllium and maybe a pinch of boron). By the time boron begins to be formed, the temperature has dropped sufficiently for fusion to cease (this is what sets the proportion of hydrogen to helium in the primordial mix). All this occurs in a total of three minutes after the moment we call the beginning. Then nothing for about 700,000 years. It is only once the average temperature of the universe drops to 3000 K (4900 F) that the electrons can remain in orbit around the protons. At that moment, something special happens. Light cannot travel very well in the presence of charged particles. Protons are charged particles and so are electrons. And the whole universe is simply a mix of free charged particles. Once the temperature drops below 3000 K, the protons and electrons join to form neutral hydrogen atoms. The universe suddenly becomes transparent (light can travel freely). All the light of the universe is suddenly liberated at once. From everywhere. And goes in all directions. That is why when we look as far back as 13.7 billion years, in any direction, we see this background radiation. Because of the expansion that has taken place since then, this light is now peaking at wavelengths which happen to be the same as the waves we use in microwave. Therefore, it is called the Cosmological Microwave Background radiation. Any other elements (carbon and heavier) were produced much later, inside stars, not by the Big Bang nucleosynthesis.

Answer 3

dunno! wasn't there..but for hydrogen fusion to take place you need to overcome the coulomb potential barrier between the two charged H nuclei, so the nuclear force can kick in.
We are assuming that the universe is large enough at this stage for the strong and electromagnetic forces to crystallize out...Approx calculation..
E requd=ke^2/r coul potential energy
Assume r=10^-15m e=1.6x10^-19coul and k=9x10^9
>E=2.3x10^-13J which is equiv to a temp of about 60million Kelvin.(non rel kinetic theory)
The universe would only have existed at that temp and above up to the strong/coul transition for the order of days before cooling and expanding. This would have been the 'window' of time and temp for nuclear synthesis. In fact knowing the hydrogen/helium ratio allowing for stars you could get a value for the H inv(T) const!
So the answer is c) further nuclear fusions were only to take place later in stars and supernovae.

Answer 4

Everything is incorrect in your question. The temperature of the singularity was much too high to permit the formation of any particles, only after a debatable time span did the point cool where particles could form. Quarks, electrons and other subatomic particles appeared and space and motion came into being. From that point on the universe evolved into its present state.

Answer 5

it not that heavy nuclei are unstable, because all elements up to iron are fused in stars and alot of others above that are still very stable.

it would say the third one. the temperature was there, but there wasnt enough pressure (density).

Answer 6

The Helium nucleus is unstable

Answer 7

perhaps because stronger alloys and heavy elements require pressure, speed and time compression. It is possible in newer planets there is helium and magnesium rather more than erbium and estroncium, due to less usage of hidrogen and some light gases.

Answer 8

all heavy nuclei are unstable

Answer 9

the temperature and density were too low--
you have to have something that creates a lot of pressure and heat (ie nova, supernova, or other explosion) to get past the carbon barrier

Answer 10

The big bang fairy that started the explosion waived his magic wand a second time.