Jellyfish who are into physics, can you please explain to me why you think there is definitive "past"?

It’s not realy physics as far as I can tell, except theoretical physics since it concerns space/time, but more along the lines of… i dont know, whtever studies that sort of thing.

I show you a movie starting with a broken bowl on a floor with a puddle of milk and jumble of cereal around it. Spontaneously it all comes back together again, cereal and milk neatly confined by the bowl and suddenly it all pitches upwards towards a kitchen table. But it slows as it reaches up and rounds the table’s edge where it then stops. You instantly know this movie is being played backwards. We don’t have any experience of things like this happening in real life.

The trouble comes in reconciling this everyday view of nature backed up by classical thermodynamics with quantum physics, where most (all?) processes are reversible. This is a big gray area in our understanding which few scientists have dared tread (one of them was Ilya Prigogine).

John Wheeler held out the prospect that the past might indeed not be definitive until a conscious entity observes evidence of it. He came up with a variant on an old parlor game to illustrate the idea.

At least one physicist, Julian Barbour, was impressed enough by the timeless Wheeler-DeWitt equation for quantum gravity that he proposed a static cosmology where time is illusory. This hasn’t met with much favor.

I’m no physicist, but physics seems unwilling to endorse our common perception of past, present and future. Einstein once wrote: “People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.”

I would like you to clarify your question. Are you asking about time or causation here? These are separate things, after all, as there could be a past without there being cause and effect relationships (in the sense of a necessary connection between events of one type and events of another type).

If you are really asking about the past, you need to also clarify what it is to “believe in” the past. There are some scientists and philosophers who believe that the past “still” has physical existence (that is, distant times exist in the same way that distant places exist even though we cannot see them from our vantage points). This is not necessary for believing in the past, however, as one can think of the past as being times that once were, but are no longer, actual.

Thanks @SavoirFaire for asking me to clarify.

It seems to me that many persons who understand quantum mechanics (perhaps better than I) assume that time’s arrow flows in a direction consistent with human experience, and build their answers and conjectures around this assumption. I am curious as to why this is assumed.

The little I know about quantum uncertainty would seems to lend itself to thinking of the arrow moving backwards from our experience. I never see persons starting from this vantage point when discussing the topic, and I wonder if I am making a fundamental error.