[TuringTourist]

I take "external power" to mean power that is not "free" as in humans paid for it. Otherwise the phrase "External power" is meaningless, as all energy comes from somewhere else eventually. (unless you're at some point in time extremely close to the birth of the universe, then we might accept that it's actually internal or at least locally sourced)

[water9]

You bring up an interesting point about the birth of the universe. Doesn’t that violate the principle that energy cannot be created?

[wongarsu]

That depends on what you believe was there the instant before the universe was created.

Answering that with "nothing" would indeed violate all kinds of conservation laws. The currently most popular theory is that time and space also started at the big bang. If that's true there is no "before the big bang", and thus the energy was always there.

Other possible answers:

- the energy was there but kind of dormant, then something triggered the big bang

- we live in a cyclical universe: after the big bang the universe expands until it reaches some maximum, then it contracts, collapses in to itself and triggers a new big bang (this seems unlikely given current experimental evidence)

- The multiverse sometimes creates "bubbles" like our universe. This is similar to spacetime starting at the big bang, but tries to explain why that happened

- Same idea, but in regular 4d spacetime: we are a kind of bubble, possibly expanding bubble, in a void filled with bubbles

- We are the inside of a rotating black hole

I'd have to go back and check how the last three reason about energy.

As you can imagine, testing any of those theories is incredibly difficult. Not impossible, but really really hard. They are more like fan theories that can be tested for internal consistency without any good hope of showing which one is true.

[10000truths]

Or, you know, an higher and/or omnipotent entity. At some point along the causal chain, there is no "testing" - you are forced to resort to metaphysical reasoning.

[DangitBobby]

This doesn't actually solve the original problem. Either something was always there or something can come from nothing, and both of those seem to violate causality as we understand it. Saying "God was always there" isn't really that different from "The universe was always there" when it comes to resolving the violation of causality.

[10000truths]

An omnipotent being would presumably have invented causality and time, and therefore not be bound by the axioms thereof.

[DangitBobby]

Sure, you can invent any explanation that you like. It just isn't more convincing than "the universe (or an outer universe giving birth to this one) was always there", since they solve exactly the same problem.

[koakuma-chan]

Obviously, something was always there. "Always" refers to the run time of our simulation.

[chowells]

At the very large scale, the universe does not appear to conserve energy. The whole "lambda" in "lambda cold dark matter" is a description of how energy is being added to the universe.