High School How would time flow for each parallel universe?

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The discussion explores how time might flow in parallel universes, questioning whether these timelines must run concurrently with our own. It suggests that if parallel universes exist, they may not be in causal contact with ours, making it impossible to measure or compare their time flow directly. The conversation highlights that if fundamental physical constants are the same across universes, time could be perceived similarly, but differing constants could lead to vastly different experiences of time. Additionally, the subjective experience of time can vary greatly depending on the observer's cognition and physical state. Ultimately, the nature of time in parallel universes remains speculative and complex.
Brennick908
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question using the parralel universe thoery if true, how would time work in other universes.
do parralel timelines have to run concurrently to our time? what I mean by this is basically if there is a version of me or you out there in a parralel universe right now in 1963 for example just living like normal or do all parralel timelines have to be in the same timeframe as us?
 
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Brennick908 said:
Summary: question using the parralel universe theory if true, how would time work in other universes.

do parralel timelines have to run concurrently to our time? what I mean by this is basically if there is a version of me or you out there in a parralel universe right now in 1963 for example just living like normal or do all parralel timelines have to be in the same timeframe as us?
I see no reason why it should but in any case it's irrelevant because since they (assuming they exist, which I don't) are not in causal contact with us we could never tell anyway.
 
I think the question is not clearly formulated, since it is not clear how one could define, even in principle, 'timelines that run concurrently between different parallel universes' (provided they exists in the first place). However, intuitively I might understand what you mean and suggest the following reasoning. If all the fundamental physical constants, such as the speed of light, the Planck constant, the fine structure constant, etc., are the same in all universes, then one can imagine (I mean 'imagine' because we don't know how to measure that anyway) the time flow indicated by the same type of clocks (say Caesium atomic clocks) running 'concurrently'. If however the physical constants are different then they do not. One second in one universe might be a million years in another.
 
You can even have a situation where a second in one Lorentz frame is a million years in another inertial coordinate system, both of them in our universe. Just accelerate something to almost the speed of light.

From an intelligent observer's viewpoint, it also matters how their own cognition senses the flow of time. You could think of some strange alien lifeform that is almost immobile like a tree or a coral and is so slow that its subjective "day" is a week for us. Like an extreme version of our folivora mammals on Earth.
 
Brennick908 said:
Summary: question using the parralel universe theory if true, how would time work in other universes.

do parralel timelines have to run concurrently to our time?

What "parallel universe theory" are you talking about? Please give a reference.
 
Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?

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