time flows differently forward and backwards:

Originally posted by joe shmo
Well, we can predict a rocks future ( albeit not indefinitely, but neither can we predict its past indefinitely with any certainty)

By we can predict its past with far greater certainty than its future. And this difference between the two is what gives rise to the illusion that we have 'experienced' the past, but that the future is still open.
Only at the quantum level does the past also start to look a bit less solid.

Originally posted by twhitehead
By we can predict its past with far greater certainty than its future. And this difference between the two is what gives rise to the illusion that we have 'experienced' the past, but that the future is still open.
Only at the quantum level does the past also start to look a bit less solid.

You are treating some hypothesised interpretations of quantum theory as established fact.


The reason we remember the past is that we have macro structures in the brain that were
changed by past events and have not yet been changed by past ones.

We could (and might) live in a completely deterministic universe where precise prediction of
the future with 100% accuracy is possible if you knew the exact state of every particle in the
universe and a complete understanding of the laws of physics (and a big enough computer).
And we would still only remember the past and not the future.

If you take a bucket of red balls and a bucket of blue balls and pour them one after another
into a glass cylinder you will have a cylinder with red balls at the bottom and blue at the top.
Which is a highly ordered state (relatively speaking) because there are far fewer ways of having
all the blue balls at the top and all the red balls at the bottom than of having them all mixed up.

Mixing the balls up takes less time/energy than un-mixing them does.

This is what makes the process 'irreversible' and have a direction.

And it's a function of the number of balls.

If you just drop in one red and one blue ball then there are very few states the system can be in,
and they are all about the same in terms of 'ordered-ness'.
And it's very easy to take the red ball out and put it in the red bucket and the blue in the blue bucket.

Originally posted by googlefudge
We could (and might) live in a completely deterministic universe where precise prediction of
the future with 100% accuracy is possible if you knew the exact state of every particle in the
universe and a complete understanding of the laws of physics (and a big enough computer).
And we would still only remember the past and not the future.

And this is where I want clarification. Why would we only remember the past and not the future? Why do we talk about deterministic only in one direction of time? If the laws of physics are essentially the same whichever way time goes, then why don't we talk about the future determining the past?

Originally posted by googlefudge
Mixing the balls up takes less time/energy than un-mixing them does.

This is what makes the process 'irreversible' and have a direction.

Am I correct in thinking that you are saying the arrow of time is entirely due to entropy and only shows up where there is an ordered stated descending into disorder?
So if we isolated an area of space where there was total disorder and over time it by chance became more ordered, within that space time would appear to flow backwards?

Originally posted by twhitehead
[quote]Time marches relentlessly forward for you and me; watch a movie in reverse, and you'll quickly see something is amiss. But from the point of view of a single, isolated particle, the passage of time looks the same in either direction. For instance, a movie of two particles scattering off of each other would look just as sensible in reverse – a conce ...[text shortened]... row of time. Surely this one directional entropy shows up even with small numbers of particles?

The entropy of evolution? I would say that time marches on regardless of entropy

Originally posted by twhitehead
Am I correct in thinking that you are saying the arrow of time is entirely due to entropy and only shows up where there is an ordered stated descending into disorder?
So if we isolated an area of space where there was total disorder and over time it by chance became more ordered, within that space time would appear to flow backwards?

The short answer is that I don't know.

The longer answer is that I don't think that time is given a direction by entropy.

Time might not in fact even exist as an entity in and of itself.

It could just be that there is a now, that keeps changing.

Originally posted by twhitehead
And this is where I want clarification. Why would we only remember the past and not the future? Why do we talk about deterministic only in one direction of time? If the laws of physics are essentially the same whichever way time goes, then why don't we talk about the future determining the past?

OK, imagine it like this.

There are particles, arrayed in space, these particles can move in space and interact by a set of rules.

There is no 'future or past' just the present, but the present keeps changing, as the particles move around
and interact according to the rules.

In that system, ordered systems will tend to become disordered, compared to earlier states, as there are
many many more ways for complex collections of particles to be disordered than ordered.
So by simple probability, entropy will increase.

This happens without the system having any 'memory' of the past. The concept of these fundamental particles
having memory is absurd. They just have their present states, which alter if and when they interact with other particles.


Now zoom out a bit.

WE are big macro objects made of countless quadrillions of these particles.
We have brains that are big macro objects that contain structures that are used to store memories.
When an event happens, it changes the structure of our brain, creating new structures that record the event.

We remember the 'past' because only events that have happened (past states of the eternal now) have altered our
minds.

Future events (while if the universe is deterministic are 100% predictable) haven't yet happened and thus have not
effected our minds to create memories.



You see in this case the past effects the future, because the next state of the ever changing now is simply the product
of the last state following the laws of physics.

Time in this doesn't really exist and doesn't have a direction.

The next state is the last state plus laws of physics, iterating along in integer steps. (because of quantum)

Originally posted by googlefudge
There are particles, arrayed in space, these particles can move in space and interact by a set of rules.

OK so far. Remember though that the hypothesis is that the set of rules can be worked in both directions of time. ie given a particular state, one can use the rules of physics to work out both future states and past states in the exact same way.

There is no 'future or past' just the present, but the present keeps changing, as the particles move around
and interact according to the rules.
And I say the present does not move at all. There is only one present and its apparent movement is an illusion.

In that system, ordered systems will tend to become disordered, compared to earlier states, as there are
many many more ways for complex collections of particles to be disordered than ordered.
And I would like to know why this is not true if we run time backwards. What is it about the laws of physics that make the system become more ordered in the reverse time direction?

So by simple probability, entropy will increase.
Does this require the existence of true randomness, or will it also be the case in a fully deterministic system? Does the fact that the laws of physics when run backwards yields greater order prove that the universe is actually deterministic in that direction of time?

This happens without the system having any 'memory' of the past. The concept of these fundamental particles
having memory is absurd.
Not at all. Their current configuration is a record of their past state (memory). A remarkably accurate record. Yet oddly enough, not a record of their future state despite the laws of physics supposedly working in both directions. This difference is what I am trying to pin down.

We remember the 'past' because only events that have happened (past states of the eternal now) have altered our
minds.

Future events (while if the universe is deterministic are 100% predictable) haven't yet happened and thus have not
effected our minds to create memories.
And I am struggling to deal with this view of things. Why do we not say that the future has also happened? Why does the future configuration of particles not equally affect our current state? Why do the laws of physics result in one directional causation? At what level does this causation operate?
In a two particle system, with only gravity and collisions allowed, would this one directional causation still exist? Would we be able to figure out the past but not the future of the system? Or would both time directions be equivalent? How many particles must be added before a difference starts to emerge?

Originally posted by twhitehead
OK so far. Remember though that the hypothesis is that the set of rules can be worked in both directions of time. ie given a particular state, one can use the rules of physics to work out both future states and past states in the exact same way.

[b]There is no 'future or past' just the present, but the present keeps changing, as the particles move arou ons be equivalent? How many particles must be added before a difference starts to emerge?[/b]

Ok. I haven't been clear.

In the example I am talking about, there is no direction of time, there is no time, period.

Time is not a thing, it has no direction, it's an illusion.


It's very hard to talk about this without using words that are time related, and saying things like before and after.

But don't confuse this for thinking that time actually exists. (it might or might not, this is just one interpretation)



Ok we have a system with some number of particles.

They all have a position and velocity/momentum and are acted on by forces according to the laws of physics.

This is the systems current state.
Neither the past nor the future exist, just the present.

However this present keeps changing. The particles move, because of their momentum and the forces acting on them.

The past is the state it was just in, the future the state it's about to be in.

The only thing that matters for determining the next state is the current one.
It doesn't matter how you got to this state, it could be instantly created in this state.
All that is needed to determine the next state is the current one.


The system doesn't 'remember' the past, it's just that the previous state 'caused' the present state, and the
state before that caused the previous state, and so on.


You could imagine a marble rolling down a board with nails in it (like this one) under entirely Newtonian deterministic physics.
http://playingwithmathematica.com/2011/04/29/a-monte-carlo-bell-curve/
http://www.karlsims.com/marbles/index.html

The present position of the marble is due to it's initial position/velocity, and its acceleration due to gravity and it's collisions
with the barriers/nails/ect on the way down.

It's current state is a result of it's past, not it's future.
The existence of further nails that it will collide with has no effect on it's present position.

If this marble were slightly soft and malleable, it would have marks on it indicating it's past collisions.
It wouldn't have marks on it representing collisions that haven't happened yet.
Thus the marble has a memory (of sorts) of it's past but not the future.

The past has left an imprint by determining the present state.
The present state will determine what the future state is.

Our memories are like the marks left in the marble, they are caused by the past and not the future.

Originally posted by googlefudge
The only thing that matters for determining the next state is the current one.

Or the next one, if the laws of physics are identical in both time directions.

The system doesn't 'remember' the past, it's just that the previous state 'caused' the present state, and the
state before that caused the previous state, and so on.
So why doesn't causation work equally well in the other direction?

It's current state is a result of it's past, not it's future.
And I want to know why this is.

The existence of further nails that it will collide with has no effect on it's present position.
Why not? I say they do. In fact, I claim that the future position more accurately determines its current position than the past position does.

If this marble were slightly soft and malleable, it would have marks on it indicating it's past collisions.
A form or memory.

It wouldn't have marks on it representing collisions that haven't happened yet.
And I am trying to identify why exactly, if the laws of physics are identical in both directions, does this 'memory effect' only happen in one direction?

The past has left an imprint by determining the present state.
The present state will determine what the future state is.
And I say the opposite. The present state tells us what the prior state was, but does not determine the future so accurately. Therefore the future is a better predictor of the past than the past is of the future, and this is the reason the past leaves an imprint on the future and not the reverse.

Originally posted by twhitehead
Or the next one, if the laws of physics are identical in both time directions.

[b]The system doesn't 'remember' the past, it's just that the previous state 'caused' the present state, and the
state before that caused the previous state, and so on.
So why doesn't causation work equally well in the other direction?

It's current state is a re this is the reason the past leaves an imprint on the future and not the reverse.[/b]

"Or the next one, if the laws of physics are identical in both time directions."

No, you're not getting it.
There is no time direction for there to be a 'in both of'.

Say you have a ball sitting on an inclined plain.

It's attracted downwards by gravity.

In it's first state it's stationary near the top of the board but accelerating downwards because it's pulled by gravity.
In the next state it's now moving down the board, and accelerating downwards because of gravity.

It's not moving backwards up the board because gravity is pulling it down and not up.

The direction of time (which doesn't exist in this interpretation) doesn't determine which way it rolls.
It always rolls down and not up because down is the direction gravity pulls it.

It's path is effected by the things it encounters on the way down, and is not yet effected by the things it
has not yet hit/encountered.

Originally posted by googlefudge
No, you're not getting it.
There is no time direction for there to be a 'in both of'.

Yes, I am definitely not getting it. You keep saying there is no time and no time direction, yet the next moment you say 'the first state', then 'the next state' clearly introducing time and giving it a direction.

Let me ask it in a different way. Given say 20 states of a 20 particle system all arranged in a row. Would it be possible to work out which direction they went through time ie could one determine that for two adjacent states A and B that A came after B and not before B?

PS: I am not trying to prove a point or 'make trouble' or anything, I truly want to understand this topic as it is a question I have long had but never really got worked out. If I challenge anyone it is not to prove them wrong but to help clarify.

Originally posted by twhitehead
PS: I am not trying to prove a point or 'make trouble' or anything, I truly want to understand this topic as it is a question I have long had but never really got worked out. If I challenge anyone it is not to prove them wrong but to help clarify.

No I get that, I'm just trying to find a way of explaining something that makes total sense to me in words that someone else can understand...

I'll have a think and get back to you.

Originally posted by twhiteheadThere is no 'future or past' just the present, but the present keeps changing, as the particles move around
and interact according to the rules.
And I say the present does not move at all. There is only one present and its apparent movement is an illusion.[/quote]

That seems to me to imply that, for example, your birth and your reading this post and your death all happened in a single instant.