Present problem

[Notanotherusername]

Is there such a thing as "now?" If so, is it out there, in the external world (whatever that it is) or a construct of the mind?

[AD1]

I'm puzzled, what does this have to do with physics?

[Notanotherusername]

It's a problem related to the nature of time. I'm interested in what aspects of time - in this case, what we refer to as the present moment - are intrinsic properties of the external world, artifacts of consciousness, or a combination of both. What is the status of "now" in physics?

[ProCop]

"The ontology of materialism rested upon the illusion that the kind of existence, the direct 'actuality' of the world around us, can be extrapolated into the atomic range. This extrapolation, however, is impossible . . . Atoms are not things." Werner Heisenberg

[James R]

It's an interesting question.

I don't think I'm aware of any physical theory for which the idea of "now" is important. "Now" seems to be a property which is unique to an individual observer's perception.

In fact, few physical theories make any important distinction between past and future, either. Many theories are time reversible, in that if you take the relevant equations, you can replace t with (-t) and it makes no difference. There are a few exceptions, which give rise to the well known "arrows of time". The main areas where past can be distinguished from future seem to be in thermodynamics, cosmology and certain aspects of quantum physics, apart from questions of psychology.

[Crisp]

...certain aspects of quantum physics...

Are you refering to the measurement proces here, or did you have something else in mind ?

Bye!

Crisp

[blobrana]

Are you referring to the measurement process

Hum,

If you view time as a spacial dimension , then the view of `now` can be likened to a point in space.
(zero dimensional point - er, in reality perhaps a string-thing of Planck length 10^-32) and would correspond to the Planck time scale of 10^-43.)

[Pete]

You can have an unambiguous point in space-time, but you can't define an unamiguous point in space, nor an unambiguous point in time.

ie if you specify a point in space at a point in time, you can't specify the same location at a different time, and you can't specify the same time at a different location.

[blobrana]

You can have an unambiguous point in space-time, but you can't define an unamiguous <unambiguous> point in space, nor an unambiguous point in time.

ie if you specify a point in space at a point in time, you can't specify the same location at a different time, and you can't specify the same time at a different location.

What!?
The difference between time and space is the way that the super-symmetry was broken and the underlying configuration of super-string/membranes dictates the way that space and time (imho) is quantisised...

<Or is my reality different from your?>
I would say that yes, you can specify the same location at a different time...
And you <b>can</b> specify the same time at a different location.
</Or is my reality different from your?>

[Pete]

Only if you also specify an arbitrary reference frame.

[James R]

Yes, Crisp, I was thinking about the measurement process.

[Notanotherusername]

I'm trying to avoid making too much of a philosophical or metaphysical issue of this but it does seem that there's a gulf between what we directly experience -- or think we experience -- as "now" (a more-or-less singular moment in time) and the almost complete absence of any conception of the present in physics. Einstein's "block universe" effectively sees all of space-time as a static whole. There's no notion in physics of future becoming past as the wave front of now progresses along. There's no allusion in science to particular moments at all. I think it's an extraordinary puzzle. Here we are, made of physical components, our bodies (and presumably our minds) arising as the result of physical laws. Yet what we experience -- the passage of time and the existence of a special, unique moment -- is nowhere represented in science. Does consciousness exist in time or is time an artifact of consciousness?