[allan marsh (OP)]

So there is past, present and future..... So how long does the present last?

[evan_au]

It takes about 100ms to process auditory information, and 300ms to process visual information, and yet they seem simultaneous*.
So I would have to say that "the present" lasts at least 200ms=300ms-100ms.

But because of the mental processing delays, "the present" is always 300ms in "the past".

*There was the intriguing case of a man who suffered a brain injury so this mental synchronisation was lost. His first symptom was that he thought the TV was broken, because he could hear the sound before the picture moved - but everyone else thought it was OK.

[mxplxxx]

This seems to be an unresolved question in physics. There are those who think the present is eternal and that the past and future are just different states of the present. This sees the universe as a finite state machine which, in effect, means we are living in a type of computer. Given that the laws of the universe are so outstandingly mathematical in nature, this is not a totally unreasonable possibility.

[allan marsh (OP)]

Sorry, my question does not refer to the human species!
I am not even asking on behalf of the fly!

I am asking about reality...... The past is real and the future unknown (unless you believe that the future is already set)
So, forgetting the poor human mind, do I assume that now is zero time.... If not what

[dlorde]

I am asking about reality...... The past is real and the future unknown (unless you believe that the future is already set)

Is the past 'real'? events have happened, and their consequences are with us, but the events themselves don't exist any more.
Is the future entirely unknown? even allowing for quantum uncertainty, we can often make reasonably accurate predictions about the future - and how definitive is our knowledge of the past? Our senses, perceptions, and memories are pretty unreliable, and our recording instruments pretty limited in scope. In both future and past extents, the reliability of our knowledge declines with time (although far less rapidly in the past than the future).

So, forgetting the poor human mind, do I assume that now is zero time.... If not what

What do you mean by 'zero time'?

There isn't any one particular 'now', each observer has their own. As has been mentioned, experiential 'now' lags behind local events by at least 300 ms, so it's a pretty vague concept. 

[allan marsh (OP)]

i did say forget the human with its 200ms delay which is just an electrochemical delay in the human brain.
i mean just how long is now..... forget humans!!!!

[mxplxxx]

Problem is, according to quantum physics, that without an observer there is likely to be no "now"! "Now" in this scenario may well exist for Planck time seconds (5.39106(32) × 10−44 s) - but this is just a guess on my part. According to relativity, "now" is different for two frames of reference whose speed/direction varies relative to each other (think of the space traveller who comes back younger than his counterparts who stayed on earth). Mind boggling stuff!!! In this scenario, now may exist for a particular frame of reference until it interacts with another frame of reference.

[allan marsh (OP)]

you are getting there with planck 10 to the power minus 34 cm in size and after that a new entity
badly named nothing.
this really gets to my main question which was about nothing.

that dear piece  of rock with no brain has only a past and perhaps a future, even if it changes from matter to energy.....yes the now is only a figment of our slow brain concocting a now reality.

so in fact now does not exist which lead us to the following conclusion.........read on later1

[dlorde]

i did say forget the human with its 200ms delay which is just an electrochemical delay in the human brain.
i mean just how long is now..... forget humans!!!!

Now depends on the observer, whether human or otherwise. It's the time at which an event occurrence is observed by some observer.

in fact now does not exist which lead us to the following conclusion...

No, it does exist; it's just dependent on the observer's inertial frame. That's what Special Relativity is about; relativity of simultaneity. Time, distance, and therefore speed, are frame-dependent.

[Lovelle]

I have the answer you want but I can't tell you now (no pun intended). I plan to use this information to make money and improve my life. Several others have this answer. We know them as powerful and sucessful people. I came across this realization while I was alone.
I can tell you that "knowing" will unravel your existence.

[dlorde]

I can tell you that "knowing" will unravel your existence.

I'd prefer not to have my existence unravelled...

[PmbPhy]

So there is past, present and future..... So how long does the present last?

The present is an instant in time and as such does not have a duration so you can say that it lasts for zero seconds. Evan is talking about human perception and not about physics so it doesn't really apply to this question.  mxplxxx is wrong in that this is far from being an unresolved problem in physics. Its not even classified as a problem in fact since there has never been anything mysterious about it to physicists.

So as you wisely caught on, Evan and mxplxxx comments don't apply, especially his comments on quantum mechanics since they're only in his imagination and not really from quantum mechanics. I.e. his comment according to quantum physics, that without an observer there is likely to be no "now"! is without any foundation. I suspect he created it himself.

So my answer stands. It should be noted that my answer pertains to physics only and not to daily life like Allan's does. What he's talking about is in Wikipedia at http://en.wikipedia.org/wiki/Present

The one that pertains to physics is in relativity. See the spacetime diagram in that webpage and notice the t = 0 plane. That plane represents the present.

I hope that helps? I believe that is exactly what you were looking for, is it not?

[alancalverd]

now = δt as t→0, as far as we know.

Delta functions are very interesting, being infinitely differentiable, unlike quantum functions. Until someone demonstrates quantised time, the continuum description of now seems adequate. 

[TommyJ]

“The only reason for time is so that everything doesn't happen at once.” - Albert Einstein.
He postulated that time was more like a river, ebbing and flowing depending on the effects of gravity and space-time and also mentioned that ‘now is an illusion’.
The most accurate clock in the universe would probably be a rotating star like a pulsar, but on Earth atomic clocks provide the most accurate track of time.

[Zer0]

That which has passed, set in stone, is the Past.

That which is undecided, uncertain, is the Future.

& what is right Now, is a Gift, reason it's called Present.
🎁

We do have a past & a future, but we always exist in the present.

PS - Trying to find the Onion by peeling away the skin of the Onion layer by layer will not help to find the Onion.
🍭

[Colin2B]

We do have a past & a future, but we always exist in the present.

When I walk along a path, I rarely ask why am I here and not where I’m going or why can’t I be where I started from. Isn’t it strange that I’m always at one point of distance rather than where I’ve been or where I’m going.
Having said that, I always feel that I’m travelling backwards in time. My seat faces backwards so I can only see where I’ve been and not where I’m going.

[TommyJ]

Time is as perceived by an observer. What is now then for an observation?

When probability was introduced to the core picture of reality, no longer the universe was no longer deterministic. Borne rule: predicting the outcome of the experiments.
When you are not looking, the wave function works according to the Shrodinger equation. But when you make a measurement, Probability(x)=I amplitude(x) I^2 (I-wave function).
The observation is in the superposition of the quantum particle state (human species also consist of quantum particles.

There are three essential components of the observed ‘now’ state.

Superposition: quantum objects can be in two different states at the same time. It was never actually observed (except double slit experiment).

Entanglement: after particles interact they become a single wave function. When we measure the state of one entangled electron, we know the state of the second one at the same time.

Measurement: postulate was added as a second set of rules to connect the math of quantum mechanics to what we actually observe. Single fraction of reality.

[Zer0]

" Having said that, I always feel that I’m travelling backwards in time. My seat faces backwards so I can only see where I’ve been and not where I’m going. "

Remarkable Thought.
🍭

A bit scary, not knowing where one is heading towards.
It's not the high cliffs that the future might hold, that one worries off.
It's the pitfalls of the past that one fears.