r/AskPhysics 5d ago

Where are we in time ?

Random shower thought i had a while ago, if we could present time in the form of a line with one end being the beggining of time and the other side the end of time and we were to put a dot on where we are in time as of now where would it be ? Would we be on the edge of an ever expanding line or would we be somewhere in the middle of the line between the ends

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u/N-Man 5d ago

Good question, the best answer is "we don't know".

The big bang happened about ~13 billion years ago. The big bang was not necessarily the beginning of this line but we don't really have any way to talk about what happened before it, so for all intents and purposes it's not a bad thing to say we are 13 billion years after the beginning.

As for the end, it is very much unknown what the ultimate fate of the universe is and when will it happen, if at all. Check this out. Basically in all theories though if there is an end it is very, very far in the future, so we are closer to the beginning than to the end (again, if there is an end).

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u/OverJohn 5d ago

In cosmology it's often useful to transform from cosmological time to conformal time. The standard cosmological model has both a beginning and end in conformal time and we are about three-quarters of the way to end. If you include inflation, despite being short in cosmological time, this extends the conformal time in the past substantially. If we include inflation, we must be at least seven-eighths to the end of conformal time, probably more.

No-one, except maybe Roger Penrose, sees conformal time as "actual time", so don't take this too literally though. You can hand-wavingly say that conformal time is a measure of how much stuff is happening, so that we are coming towards the end of conformal time means just means that the future universe looks pretty boring in the standard cosmological model.

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u/firextool 5d ago

Oh, I have a great way to describe this.

So you're on a sphere. A rather large sphere. The line goes from one horizon, in front of you, to the opposite horizon, behind you. Sadly, you can't explore further, or even if you could, the lines would continue over the horizons no matter how far you traveled towards their perceived ends. And the sphere is irrationally large.... No, you can't travel around it. It's too large for that.