The World of Leftover Energy

Question from Andrew:
Why do atheists like Stenger say that the universe can be eternal, when this does not hold?

Stenger argues that the universe can be eternal, non-created, extrapolating the law of conservation of energy-mass before the planck time, he says that because we do not see a violation to this law, the universe can perfectly be eternal.

But this is a fallacy as William Lane Craig exposed once. If the energy were eternal there would be no useful energy right now, it would have become useless, complete entropy an infinite time ago, and because we do not see this, the only conclusion is that the universe and the energy began a finite time ago. Where we Christians think, the best explanation is the creation by God.

Answer by SmartLX:
Even according to you, Stenger only said the universe can be eternal, not that it definitely is. If it isn’t, then God is only one possibility among who knows how many: spontaneous emergence (more on that in a sec), a previous universe, a deistic rather than theistic (let alone Christian) god and so on.

Anyway, there are at least three straightforward ways in which there can still be useful energy now after an eternity of existence. There might be others, but even one possible way is enough to keep someone like Craig from ruling out the possibility entirely.

1. There is infinite or potentially infinite energy as well as infinite time.
Our universe as we see it has existed for a finite amount of time since the Big Bang with a certain amount of matter and energy, but what if that only contained one portion of the available material of an endless universe or multiverse? Or can matter emerge regularly and spontaneously from the quantum foam as much as it likes, as long as the same amount of antimatter accompanies it and the total amount of “positive” energy stays constant? As Lawrence Krauss says, something can come from nothing if “nothing” is unstable.

2. The energy is periodically reclaimed.
Entropy doesn’t destroy energy (hence Stenger’s point), it only ends up radiating it towards the edges of the universe where it’s no use to anyone. If Big Bangs are regular rather than one-off occurrences, then there’s a long-standing hypothesis that the universe is first drawn together in a Big Crunch. The new singularity contains not only all the matter and energy of the crushed universe, but all the space as well. Whatever was lost to entropy is dragged back to a mathematical point, just like at the point of our own Big Bang, and the cycle can begin again.

3. The amount of available energy decreases exponentially.
The less energy there is, the slower it dissipates, the way a gush becomes a trickle when you tip out a bucket of water. Say that every billion years, the amount of available energy decreases by half. If so then a billion years ago there was twice as much, and two billion years from now there’ll be a quarter as much, but there will never, ever be none. It will approach zero (or, importantly, a non-zero constant) asymptotically, which is to say it will get closer and closer without ever reaching it. Perhaps the amount of energy we’re used to seeing in the world is practically nothing compared to the intense heat, light and motion that was everywhere in times gone by, with the universe in a state of near-saturation (perhaps asymptotically again). Without past reference points from before the Big Bang, which are probably impossible to attain, you can’t make a judgement that there can’t be this much energy now.

One final point: be very careful about expressions like “the best explanation” when discussing cosmology. If quantum mechanics have taught us anything, it’s that reality can be counter-intuitive, and the truth might well strike one as ridiculous. If there’s evidence for a claim then it’s a supportable claim, but if all it does is sound right then it’s worthless.

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