What Came Before the Big Bang? Exploring Pre-Universe Matter and Energy

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SUMMARY

The discussion centers on the philosophical and scientific implications of what existed before the Big Bang, challenging the notion that all matter and energy emerged from a singularity. Participants argue that fundamental forces and laws of physics were outcomes of the Big Bang rather than pre-existing conditions. Key theories mentioned include the Hartle-Hawking universe and Loop Quantum Cosmology, which propose alternative models to explain the universe's origins. The conversation highlights the speculative nature of current cosmological theories and the lack of definitive evidence regarding pre-Big Bang conditions.

PREREQUISITES
  • Understanding of fundamental forces in physics
  • Familiarity with cosmological theories, particularly the Big Bang theory
  • Basic knowledge of quantum mechanics and general relativity
  • Ability to interpret scientific literature, such as "quantum cosmology for pedestrians"
NEXT STEPS
  • Research the Hartle-Hawking no-boundary proposal
  • Explore Loop Quantum Cosmology and its implications for the universe's origins
  • Investigate the concept of quantum tunneling and its relation to the Big Bang
  • Read literature on the conservation of energy and matter in the context of general relativity
USEFUL FOR

Astronomers, physicists, cosmologists, and anyone interested in the foundational questions of the universe's existence and the nature of reality prior to the Big Bang.

  • #31
Drakkith said:
Care to elaborate? I don't know why you wouldn't use something like potential energy in this situation.
Well, since you'd usually use Newtonian gravity in this situation, you probably would. But my point is that when you work with General Relativity, there simply isn't any potential energy term there, and furthermore there is not even any good way to define one in general.
 
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  • #32
Chalnoth said:
Well, since you'd usually use Newtonian gravity in this situation, you probably would. But my point is that when you work with General Relativity, there simply isn't any potential energy term there, and furthermore there is not even any good way to define one in general.

Alright, then is this even an issue in GR?

And is GR the only thing to look at here in regards to conservation of energy?
 
  • #33
Drakkith said:
Alright, then is this even an issue in GR?

And is GR the only thing to look at here in regards to conservation of energy?
Well, it's a conceptual issue, to be sure, as many people have a hard time understanding that conservation of energy is only an approximate, local law, one that simply does not hold globally.

The main issue here is that conservation of energy stems from invariance in time. That is, if you can take a system and examine it at two different times and the system remains the same in some specific mathematical sense for those two times, then energy is necessarily conserved between those two times.

Most of the physical laws we know and love, whether they be Newtonian physics, or electricity and magnetism, or quantum mechanics all are unchanged in time, and so they all follow energy conservation. General Relativity throws a wrench into this whole thing because it makes the time coordinate arbitrary: if you can change your very definition of what you mean by "time", then the very idea of "time invariance" ceases to have meaning, and so while you might be able to write down a specific system where energy conservation holds, in general it just won't.
 

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