Why women look in Mirrors?

[carnyx]

(This thread was originallty titled "Another thread on the Arrow of time" but this was lazy of me, and did not repect Abacus's original thread. I apologise)

Can we see time reversal?

I thought that this exercise might be best as a separate thread;

Personally I have my doubts about the 'arrow of time' metaphor, becase I suspect it is a necessary bit of blab to cover up the irritating fact that the 't' of Newton's and Maxwell's formulae can go negative but the sums still work.

So here is a thought experiment, to see if the 'arrow of time' can be reversed.

Point a real arrow, head first at a mirror. Check the time taken for the light from the real arrow's head, and also the real arrow's rear flight feather, to reach your eye. Now compare these timings with the same values taken for the light to get via the mirror from the tip to your eye, and from the tail via the mirror to your eye.

Is the reflected arrow image pointing backwards?

Is time in the reflection going backwards, too?

[carnyx]

NM's comment on another thread has prompted me to post a clarification

Here is the experimental setup;

Take a classical arrow, 1 foot long, complete with with an arrowhead and tailfeathers.

Point it at a mirror so that the distance between one's eye and the tail is 1 foot, and the arrowhead-mirror distance is 1 foot from the mirror surface. ( and of course .... the eye is 3 feet from the mirror)

Now light travels at a certain speed, so the time taken is directly proportional to distance travelled
and so T and D are effectively equivalent.

First we look at the time delay T between the light from the head and the tail of the real arrow and our eye;

So, 2T-T = +T

Then we look at the time delay between the light from the head and the tail of the real arrow and our eye, via the mirror;

(T + 3T) - ( 2T + 3T) = 4T -5T = - T

Negative T?

Apparently a mirror reverses time!

(No wonder women like them)

[abacus9900]

Time reversal is not possible because of the 2nd. law of thermodynamics which states that matter tends towards disorder. In other words, there is no way disorder can be reversed, so the arrow of time can only be in one direction.

[Progenitor A]

Mar 8, 2011 10:11:18 GMT 1 abacus9900 said:

Time reversal is not possible because of the 2nd. law of thermodynamics which states that matter tends towards disorder. In other words, there is no way disorder can be reversed, so the arrow of time can only be in one direction.

;D
Being a bit literal here Abacus!
Think of it as an ordinary arrow! ;D

[Progenitor A]

Mar 8, 2011 9:58:48 GMT 1 carnyx said:

NM's comment on another thread has prompted me to post a clarification

Here is the experimental setup;

Take a classical arrow, 1 foot long, complete with with an arrowhead and tailfeathers.

Point it at a mirror so that the distance between one's eye and the tail is 1 foot, and the arrowhead-mirror distance is 1 foot from the mirror surface. ( and of course .... the eye is 3 feet from the mirror)

Now light travels at a certain speed, so the time taken is directly proportional to distance travelled
and so T and D are effectively equivalent.

First we look at the time delay T between the light from the head and the tail of the real arrow and our eye;

So, 2T-T = +T

Then we look at the time delay between the light from the head and the tail of the real arrow and our eye, via the mirror;

(T + 3T) - ( 2T + 3T) = 4T -5T = - T

Negative T?

Apparently a mirror reverses time!

(No wonder women like them)

;DVery crafty!

[abacus9900]

Mar 8, 2011 10:17:37 GMT 1 Progenitor A said:

Mar 8, 2011 10:11:18 GMT 1 abacus9900 said:

Time reversal is not possible because of the 2nd. law of thermodynamics which states that matter tends towards disorder. In other words, there is no way disorder can be reversed, so the arrow of time can only be in one direction.

;D
Being a bit literal here Abacus!
Think of it as an ordinary arrow! ;D

Well, Brian Cox gave the example of a piece of ice falling into the sea, remember? He said, in principle at least, the falling ice could reverse and go back up and rejoin the place from where it had fallen but the chances of this are so vanishingly small that it would not happen. And that's just one event let alone any other event reversing too.

[abacus9900]

Mar 7, 2011 20:10:09 GMT 1 carnyx said:

(This thread was originallty titled "Another thread on the Arrow of time" but this was lazy of me, and did not repect Abacus's original thread. I apologise)

Can we see time reversal?

I thought that this exercise might be best as a separate thread;

Personally I have my doubts about the 'arrow of time' metaphor, becase I suspect it is a necessary bit of blab to cover up the irritating fact that the 't' of Newton's and Maxwell's formulae can go negative but the sums still work.

So here is a thought experiment, to see if the 'arrow of time' can be reversed.

Point a real arrow, head first at a mirror. Check the time taken for the light from the real arrow's head, and also the real arrow's rear flight feather, to reach your eye. Now compare these timings with the same values taken for the light to get via the mirror from the tip to your eye, and from the tail via the mirror to your eye.

Is the reflected arrow image pointing backwards?

Is time in the reflection going backwards, too?

That's because the speed of light is finite and takes time to reach an observer. We see this when we look at the stars where what we see now is the past because it took light a finite time to reach us. The further we look into space the the further back in time we are seeing.

[carnyx]

@abacus,

He said, in principle at least, the falling ice could reverse and go back up and rejoin the place from where it had fallen

In fact, the molecules really do reverse and go back up and rejoin the place from where is had fallen! Water molecules evaporate, form solids, which falls as snow, and is compacted to form a glacial ice, which slowly moves down to sea level, where the ice fall off and rejoins the waters. Nothing magical .. it has been happening for aeons!

And re the odds of it happening .. do the sums, and then you can cancel out most of them, because it has aready happened, and will continue to happen, all round the world.

As I said elsewhere, I believe Cox uses a crap example ... a metaphor to explain a piece of metaphysics, which in turn is necessary in order to get a piece of straight physics to prop up a dodgy cosmology (aka a religiose belief-system).

[robinpike]

Asking if 'time reversal' is possible is bit of a red-herring.

Time is present because of change - it doesn't have a direction. Either change is happening, and therefore time is present, or everything is unchanging, and therefore time is absent.

It's a bit like length: you can have a rod with a length, but not a rod with a negative length.

[Progenitor A]

Mar 9, 2011 13:46:30 GMT 1 robinpike said:

Asking if 'time reversal' is possible is bit of a red-herring.

Time is present because of change - it doesn't have a direction. Either change is happening, and therefore time is present, or everything is unchanging, and therefore time is absent.

It's a bit like length: you can have a rod with a length, but not a rod with a negative length.

But that conflicts with the 'arrow of time' that Professot Cox spent an hour talking about

(Do you see the trick in Carnyx's example?)

[abacus9900]

Time is present because of change - it doesn't have a direction.

It does because matter tends towards disorder which is why you cannot 'undo' events. Why do you think the sun eventually burns out or why we age and grow old and die?

The 2nd. law of thermodynamics.