Ruwan, UK asked:
If the universe has always existed like some people believe shouldnít all the hydrogen by now have changed into helium or some other heavier elements? Are there places in the universe that make hydrogen from other subatomic particles?
Ben - So if there was never a Big Bang, weíve always had stars around - we know that what happens inside stars is hydrogen is converted into heavier elements like helium. If there was no Big Bang then surely by now all the hydrogen would have been used up, is that right Sarah?
Sarah - Well yes. The idea that the universe has already existed is known as the Steady State theory. This was developed in the 40s as an alternative to the Big Bang theory which is that the universe came into being and began to expand about 13.7 billion years ago. The Steady State theory has lost favour since the 1960s because a lot of the evidence actually supports the Big Bang theory, particularly after the discovery of cosmic microwave background radiation which is the sort of thing that the James Webb telescope will be looking for.
Ben - And itís actually some of the stuff that you pick up on static on your TV.
Sarah - Exactly, and on your radio as well. You might think that even after 13.7 billion years the hydrogen might have all been converted but hydrogen still makes up about 75% of the normal matter in the universe.
Diana - Thatís quite a lot, isnít it? Why is there so much still out there?
Sarah - Most of itís actually in low density, low temperature clouds of hydrogen where there just isnít enough energy to fuse the nuclei to make helium or other elements. This isnít a spontaneous reaction. It takes a serious amount of energy to do it which is why it did happen a second or so after the Big Bang and why it still happens in stars like our own sun. The heat and the energy present is there to do it but it just isnít there elsewhere in the universe.
Ruwan asked the Naked Scientists:
The hydrogen that we have around us was one of the (most abundant) products of the big bang.
Hydrogen is being created all the time: a solitary neutron has a half life measured in minutes It decays into an electron and a proton (hydrogen). There are many ways a neutron can leave the stability of the nucleus two very common causes are cosmic ray or alpha particle collisions chris yukna science general chris yukna, Sat, 1st Jan 2011