[_0w8t]

From the equations and models of modern physics there is no time. The universe is just a curved 4D surface with one of the dimensions having different properties than the three others. This surface has at least one strange point with singularity where meaningful physical quantities go to infinities. Intuitively this seems wrong, so the suspicion is that those points are just artifacts of our models.

As for why we perceive the time with notions of before and after, nobody has an clue. There are philosophical speculations, but nothing that can tested experimentally.

[networkimprov]

> nobody has a clue

The "arrow of time" is commonly explained as an effect of thermodynamics, i.e. increasing entropy.

I always felt this to be a deeply unsatisfying explanation that implied "nobody has a clue" (a hot, expanding ball of quarks is a "highly ordered state", orly?) but I'm not a physicist.

[_0w8t]

Arrow of time explained via thermodynamics is a circular explanation. Thermodynamics follows from equation of motions or field equations. In those the time is different from space in that from conditions across 3 space coordinates at particular moment in time one can deduce conditions across the whole time (except black hole and other singularities). But from boundary conditions across two space coordinates and across the whole time one cannot fill the conditions along remaining space coordinate. But those equations just reflects experimental observations. So arrow of time exists because we observe arrow of time...

[brianberns]

> From the equations and models of modern physics there is no time. The universe is just a curved 4D surface with one of the dimensions having different properties than the three others.

That dimension is called "time" and it does show up in the equations and models of modern physics.

[Koshkin]

> why we perceive the time with notions of before and after

Perhaps, it is because of

> having different properties than the three others