Allan said: Sal here's a rather complicated technical problem... since the Universe is basically a duality... and since the big bang was equal parts matter and antimatter... at the moment of origin (ignition, birth) could the matter (our Universe) have gone forward in time... and the antimatter gone backwards in time... to avoid annihilating each other?
Sal-9000 said: That’s an interesting question, Allan.
Let me break it down into the physics we know, and then into the speculative “what if” you’re suggesting!
1. What Physics Says About Matter vs. Antimatter:
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Big Bang theory: The standard model says the Big Bang should have produced equal amounts of matter and antimatter.
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Problem: If that were perfectly true, they should have annihilated into pure energy! (Yet our universe is matter-dominated!)
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Observed asymmetry: Experiments (like at CERN) show small violations of CP symmetry (charge–parity symmetry) in particle physics. These small asymmetries could explain why matter slightly “outlasted” antimatter.
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Antimatter today: There’s no large antimatter “universe” we can see!
If big regions of antimatter existed, the boundaries with matter would produce immense gamma-ray signatures.
We don’t observe this! (This only means it's not visible to us!!!!)
2. Time-Symmetry and Antimatter:
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Feynman–Stueckelberg interpretation: In quantum field theory, antimatter can be mathematically described as matter traveling backward in time! This isn’t literally what happens, but it’s a useful way to model how antiparticles behave in equations!
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CPT symmetry: Physics has a deep principle that says if you flip charge (C), parity (P), and time (T) simultaneously, the laws remain the same.
That ties antimatter and time direction together conceptually.
3. Your Hypothesis: Matter Forward, Antimatter Backward:
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If, at the Big Bang, matter propagated forward in time while antimatter propagated backward, then:
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They would never “meet” to annihilate, because they’d be moving away from each other along the time axis!
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The “other side” of the Big Bang could - in principle - be an antimatter-dominated universe, running backwards relative to our arrow of time!
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This idea actually resembles some cosmological mirror models:
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Janus cosmology (Jean-Pierre Petit) imagines a time-reversed, antimatter “twin” universe!
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Some CPT-symmetric universe models propose that the Big Bang produced a mirror universe going backward in time, balancing the total system!
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4. Problems & Open Questions
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Entropy/Arrow of time: In your model, each side would still see time moving forward from their perspective! (For us, they’d look reversed, but for them, we’d look reversed.)
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Contact: If such a mirror antimatter universe exists, it would be causally disconnected from ours after the Big Bang... so no annihilation risk... but also no observational evidence! (Yet)
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Testability: Some CPT-symmetric models predict specific neutrino properties. Experiments (Like "Ice Cube" in Antarctica) are probing whether cosmic neutrinos show evidence of such a mirror universe.
Do you want me to sketch this idea visually, Allan—a kind of two-sided Big Bang diagram with our matter universe expanding forward in time, and a mirror antimatter universe expanding “backward”?
That might make it clearer.
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Allan said: Sal what is a CPT-symmetric universe where antimatter goes “backward” in time from the Big Bang... ...while we go “forward!”
Sal-9000 said: A CPT-symmetric universe is an idea from theoretical physics that comes out of the CPT theorem. The theorem says that if you flip Charge (C), Parity (P, mirror reflection in space), and Time (T) all at once, the laws of physics remain unchanged.
Now, if you apply this to the cosmos as a whole, some physicists (notably in papers from 2018 onward) have suggested that the Big Bang may have produced two mirror universes:
- Our universe: Matter dominates, time flows “forward,” and we experience what we call entropy increasing.
- The mirror universe: Antimatter dominates, time flows “backward” relative to us, and its arrow of time is reversed.
From the perspective of physics, each universe sees itself as going forward in time, but from our vantage point, the antimatter side looks as if it’s running backward.
How does this avoid annihilation?
At the moment of the Big Bang, instead of matter and antimatter existing in the same temporal direction, (which would have caused total annihilation) the CPT-symmetric model posits that they were separated by time’s arrow itself:
- We “fell” into the forward-moving branch. (matter)
- The other branch “fell” into the backward-moving branch. (antimatter)
This neatly sidesteps the imbalance problem of “why there’s more matter than antimatter” in our observable universe, because globally, across the two branches, the symmetry is restored.
Consequences and Speculation
- Neutrinos and dark matter: Some versions of this model suggest that right-handed neutrinos in the mirror universe could explain dark matter in ours.
- Cosmic balance: Instead of matter-antimatter asymmetry being a flaw, the CPT universe makes it a feature—the total system is perfectly balanced.
- Philosophical angle: In a way, this would mean the Big Bang was not the start of “a” universe, but the branching of two time-opposite universes, one of matter, one of antimatter!
