Time

[Bo]

well the fact that we can see antiparticles as normal particles moving backward in time is somewhat of a mathematical consequence of the theory. It basicly comes down to this: If we have the equation(s) of motion (eom) for the ordinary particle (these basicly are equations that tell you how your particle moves through space as a function of time), and we compare them to the antiparticle eom. you can see that we can switch between the 2 equations by letting time run in a the opposite direction. so a simple example:

if the eom of the normal particle is x(t) = C*t where x(t) is the position at time t, C is some constant and t is the time, then the antiparticle eom would be: x(t) = C*(-t)

But since we have (assume?) causality, (something happening at some time can only have consequences at some later time, not earlier), we see these particles (that we can mathematicly represent as normal particles travelling backwards in time) as anti-particles.

Bo

[Chitownloft]

The idea of Chitownloft of entropy i find quite nice; never heard of it. but you still have some 'chicken and the egg' discussion: Does entropy encrease because time travels in a certain direction, or does the requirement that entropy should increase forces time to travel that way? i don't know (a lot of work these days is done on evolution of entropy on cosmological scales; if annyone knows more about that i would like to know!)

 

Time appears to have an arrow “direction” because of our observation of entropy. A glass falls off a table and shatters but never collects it’s pieces back off the ground to appear in a more ordered state. The “chicken and the egg” would be a singularity, the universe would have to have started in a highly ordered state in order for entropy to explain why time appears to have an arrow or a “direction” that moves forward.

 

As I understand it entropy explains why time appears to have a “direction” in our everyday experiences.

(of course the laws of physics, namely classical relativity makes no distinction between forward or backward and hold true regardless)

[Freethinker]

Originally posted by: Chitownloft

 

(of course the laws of physics, namely classical relativity makes no distinction between forward or backward and hold true regardless)

 

If by "classical relativity" you mean General Relativity, Einstien summed it up by saying that time IS directional since "we can not remember the future".

[Uncle Martin]

Originally posted by: Chitownloft

. A glass falls off a table and shatters but never collects it’s pieces back off the ground to appear in a more ordered state.

 

Chitownloft,

Please tell me how the glass is in a less ordered state after falling off the table. I suggest it is moving towards a more ordered state. It is going from a state of grouping order to a state of symmetry order. Eventually the whole universe will be symmetrically ordered when every subatomic particle is evenly spaced throughout all of space-time.

[Freethinker]

Originally posted by: Uncle Martin

Originally posted by: Chitownloft

 

. A glass falls off a table and shatters but never collects it’s pieces back off the ground to appear in a more ordered state.

 

Chitownloft,

 

Please tell me how the glass is in a less ordered state after falling off the table.

 

When I first saw the statement, I recognized it. I ahve seen it many times before. But I did not want to assume it's source/intent. We will see if I guessed right.

[Tim_Lou]

well, i think this relates to what i learnt in chem.

 

free energy equation:

reaction favors decause in potential energy and increase in disorder.

 

delta G= delta H - T*delta S

 

i guess it is related, isnt it?

a reaction is only spontaneous when delta G is negative.

 

glass example:

delta H= - (decrease in potential energy)

delta S= + (more disorder)

 

result:

 

-h - Ts

always negative, so it works!!!

 

(dont know if its off topic....i dont really know what im posting....lol)

[Tim_Lou]

for the universe:

big bang:

 

delta H= - (i guess, releasing tons of energy.)

T= infinity

delta S= +, more disorder actually, since a point is more order than a mass of stars and galaxy.

 

so:

-H - infinity

 

delta G= very negative....

 

(thats how i relate chem to physics...lol)

[Chitownloft]

Originally posted by: Chitownloft (of course the laws of physics, namely classical relativity makes no distinction between forward or backward and hold true regardless)

 

Originally posted by: freethinker

If by "classical relativity" you mean General Relativity, Einstien summed it up by saying that time IS directional since "we can not remember the future".

 

Hmmm on further review my choice of words probably wasn’t the best. Maybe,

(of course the laws of physics are time reverse symmetric.)

 

 

When I first saw the statement, I recognized it. I ahve seen it many times before. But I did not want to assume it's source/intent. We will see if I guessed right.

 

I’m confident the analogy isn’t mine; I’ve heard/read it multiple times as a visual way to describe how the second law of Thermodynamics represents "time's arrow".

[Bo]

hmm took me a while to figure out what you where talking about, but anyways: try to say what the abbrevations mean that you use.. (there is no real standard for these things. e.g. what you call Delta G is in my thermodynamics book called dW...)

But your asumption that dH is negative for the big bang as a whole is i think wrong. I think it's zero, because the big bang is a closed system. If dH is anything from zero, the BB would lose energy to, or get energy from the 'outside BB' And that's not in the general bb theory. But that doesn;t disprove your point, the only way for the universe to expand (or just do *something*) spontanously is for the universe to increase in enthropy... But i still have some problems of introducing the direction of time here...

It is the case that the small change in work (dG) and in enthropy (dS) require some change in time (lets call it dt), but if you change the direction of time, both dG and dS (and so also the condition that dG should be negative for spontaneous processes) change sign (+ becomes - and vice versa) so everything still holds...i think

Bo

[Tim_Lou]

ppl always say a glass falls off the table will never be in ordered (unlike the universe)

 

but on the other hand, how much of a chance is the glass gonna break off into particles?

 

every piece of the broken is a galaxy...or....

 

i think...

[Uncle Martin]

The glass being broken appears less ordered than before, just as the universe seems less ordered than the singularity. What I'm saying is that there are theories that question our definition of order/disorder. I do think the singularity is more ordered than our current state, but if the big rip theory proves to be accurate flat space at 0 degrees K could also be a definition of perfect order. We may be going from one state of extreme order to another. This is just one of thousands of "outside the envelope" theories that have been presented. I am intrigued by some, some are not very credible.

 

Before the glass falls off the table, is it half full or half empty?........Or just too big?...Hmmmmm?

[Freethinker]

Originally posted by: Uncle Martin

Before the glass falls off the table, is it half full or half empty?........Or just too big?...Hmmmmm?

 

The glass is ALWAYS FULL. It is a question of "with what"?

[Uncle Martin]

Originally posted by: Freethinker

 

 

 

The glass is ALWAYS FULL. It is a question of "with what"?

 

Ah!!! I like that even better than mine.