If, time goes backward beyond t=0 then we have to think of the implications.

We then have a universe where time did not begin (for us).

Or time has existed forever. Which is a very hard concept.

All thoughts welcome.

Clockwise may be considered forward as anticlockwise isn’t.

Clocks have been made that go in either direction.

time’s like space, a where for stuff to happen. I suppose anywhere there’s stuff there’s a where and time. Maybe that’s related thermodynamic time.

then there’s tick tock time of human clocks, which invariably involves physical change and comparison of some sort.

then there’re perceptions of time.

as for the beginnings of a whatever for this universe, I suppose a bubble emerged and a property of that emergence was obliteration of any connection with the whatever that it originated.

tauto said:

If, time goes backward beyond t=0 then we have to think of the implications.

We then have a universe where time did not begin (for us).

Or time has existed forever. Which is a very hard concept.

All thoughts welcome.

Personally I find the concept of finite time harder than the concept of infinite time.

But even if we accept that time might be finite, there is no reason to suppose that it started at the local Big Bang.

transition said:

time’s like space, a where for stuff to happen. I suppose anywhere there’s stuff there’s a where and time. Maybe that’s related thermodynamic time.

then there’s tick tock time of human clocks, which invariably involves physical change and comparison of some sort.

then there’re perceptions of time.

as for the beginnings of a whatever for this universe, I suppose a bubble emerged and a property of that emergence was obliteration of any connection with the whatever that it originated.

I don’t know of any evidence that there was no connection between the current state of the Local Universe and it’s previous state.

I suppose that is a possibility, but I don’t think it should be taken as the default assumption.

tauto said:

If, time goes backward beyond t=0 then we have to think of the implications.

We then have a universe where time did not begin (for us).

Or time has existed forever. Which is a very hard concept.

All thoughts welcome.

Hmm.
“time has existed forever” is not at hard concept at all, people tend to struggle more with the opposite concept, that time began a finite time ago.

All thoughts, well.
Physics is by and large reversible. Newton’s equations of motion work perfectly well when time is reversed. Ditto Emmy Noether’s theorem that “every differentiable symmetry of the action of a physical system has a corresponding conservation law”. Ditto all Einstein’s equation of general relativity, the metric of general relativity depends on the square of time which remains the same when the direction of time is reversed.

Quantum mechanics isn’t quite reversible in time. If you reverse time then you either need to change each particle to its antiparticle or change all electrostatic charges to their opposite, negatively charged protons with a cloud of positively charged electrons around them. But quantum mechanics equations are largely reversible.

Biology, memory, shattering of glass, and the second law of thermodynamics tend by and large to be one way in time. Plants tend to grow and reproduce rather than come to life from inanimate matter, and regurgitate food as they shrink, before flinging themselves upwards into the seedpods of their parents.

So now we have a choice as to how to treat the reversal of time. If we keep our arrow of thermodynamics pointing the same way or reverse thermodynamics with time.

What now of Olber’s paradox?

mollwollfumble said:

What now of Olber’s paradox?

I would assume that a photon that has originated from a sufficiently distant object becomes incoherent to human vision but is still there………

tauto said:

If, time goes backward beyond t=0 then we have to think of the implications.

We then have a universe where time did not begin (for us).

Or time has existed forever. Which is a very hard concept.

All thoughts welcome.

One further thought, have you considered the possibility that time is neither positive or negative, but is instead imaginary, in the mathematical sense? The resulting changes in general relativity and thermodynamics then become very interesting. This startling possibility has been beautifully explored by Aussie Science Fiction writer Greg Egan in his book “The clockwork rocket”. In this universe, light has no universal speed and its creation generates energy. And plants make food by emitting their own light into the dark night sky.

Postpocelipse said:

mollwollfumble said:

What now of Olber’s paradox?

I would assume that a photon that has originated from a sufficiently distant object becomes incoherent to human vision but is still there………

can one photon become incoherent?

>I suppose that is a possibility, but I don’t think it should be taken as the default assumption

I was blowing bubbles and came up with the idea.

ChrispenEvan said:

Postpocelipse said:

mollwollfumble said:

What now of Olber’s paradox?

I would assume that a photon that has originated from a sufficiently distant object becomes incoherent to human vision but is still there………

can one photon become incoherent?

It can lose enough energy that it is below visible.

Postpocelipse said:

ChrispenEvan said:

Postpocelipse said:

I would assume that a photon that has originated from a sufficiently distant object becomes incoherent to human vision but is still there………

can one photon become incoherent?

It can lose enough energy that it is below visible.

that’s better.

:-)

Time going on forever in each direction is not something that can actually be measured, but there’s nothing wrong with it in principle.