• Question: The law of conservation of energy says that Energy can not be created nor it can be destroyed then how we can talk about the thing which can not be created?

    Asked by mustumar to Chris, Dave, David, Fiona, Jack on 25 Jun 2013.
    • Photo: Dave Farmer

      Dave Farmer answered on 25 Jun 2013:

      Hi mustumar,

      All the energy we have available in the universe came from the big bang, so we can talk about it, it’s part of our universe. As to how exactly it was created in the big bang, i.e. how did the big bang occur. I don’t think that there’s a definitive answer yet, so this is actually a very good question!

      I must admit that theories of the early universe and pre big bang conditions are far from my speciality. I’m going to throw David into the firing line on this one and suggest that he might be the man to tell you more!

      Dave

    • Photo: Jack Miller

      Jack Miller answered on 25 Jun 2013:

      Hi Mustumar,

      Conserved quantities — like energy and charge — are actually the result of symmetries in theories. In our universe, it doesn’t matter if I drop a ball onto the ground tomorrow or next week, the same thing happens — the laws of nature don’t care what your watch says. This symmetry in time is what actually gives rise to energy being a conserved quantity (through something called Noether’s theorem, after the oft-under-appreciated German physicist, Emmy Noether). The fact that physics doesn’t care if I’m in Alexandria or Alaska (i.e. the same thing happens anywhere in space) gives rise to the conservation of momentum. There are other, more mathematical symmetries, one of which (called gauge symmetry) gives rise to the conservation of electrical charge.

      It turns out that the laws describing our universe as we find it have these properties, which give rise to the conservation of energy. However, in the very early universe, there’s not much evidence that the laws of nature were as they are now. Indeed, there’s much we don’t know about the big bang (or big bangs) and why the laws are the way it is now is a question that we’re currently unable to really answer.

      However, we do know that there is this conserved quantity called energy, and it’s bloody useful for solving problems. We can explain it in terms of a deeper symmetry, but there’s no a-priori reason why that symmetry has to be there, as opposed to a universe that’s much more exotic and weird.

      Hope that helps!

      — Jack

    • Photo: David Freeborn

      David Freeborn answered on 25 Jun 2013:

      Hi mustumar,

      Dave & Jack have already given some pretty good answers here.

      As to how energy was created in the first place… well, there are a lot of answers physicists have given. None of them are totally satisfactory.

      (1) Energy might have come out of a quantum fluctuation. Heisenberg’s Uncertainty Principle lets the Universe violate conservation of energy for a very brief amount of time. A process called “inflation” could then have rapidly expanded a quantum fluctuation, causing the Universe to come into being. So the Universe might be a quantum fluctuation on an epic scale. This is probably where most physicists currently lean towards.

      (2) The Big Bang might have already contained all of the Universe’s energy: if ti emerged from a black hole or a previous Universe’s big crunch. I intuitively like this answer.

      (3) It might be “meaningless” to talk about “before” the big bang, because there was no time before the big bang anyway. As we go backwards, approaching the big bang, time slows to a point where it is infinitely slow, known as a “singularity”. It might not even be meaningful to talk about a moment “before” the Big Bang. At this moment itself, there was huge gravitational energy, from holding all the mass of the Universe together at a single point, before it exploded outwards.

      If you don’t find any of these ideas totally satisfying, you’re not alone. I don’t either. More/better ideas are needed here!

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