Time Arrow: Entropy & Energy - QP Explored

In summary, there is a debate about whether time has an arrow or direction. Some suggest it is influenced by entropy, while others argue that it is a philosophical concept explaining why processes happen one way and not in reverse. Energy can move in either direction, but entropy is constrained by a law that defines its change, creating the "arrow of time" effect. The terms "order" and "disorder" in physics refer to equilibrium and motion, rather than a goal for matter to achieve. There is no evidence for a time-reversal symmetry, and time does not actually "move" in any direction, but is a measure of motion.
  • #1
shaun11
6
0
I have only recently started reading about QP and there seems to be a big question mark on whether time has an arrow (direction). There seems to be a tendency leaning towards entropy having an influence on this topic. This is that, time moves in accordance to order vs disorder - the arrow facing in the direction of objects moving from order to disrder. My question: is it possible that the time arrow could point relative to objects loss of energy?
 
Physics news on Phys.org
  • #2
I'm struggling to understand what you're asking here.

As I understand it, the 'arrow of time' is simply a philosophical explanation for why processes happen one way but don't immediately undo themselves. We postulate that entropy can never decrease; so that's a constraint on the passage of time - that processes can't happen in 'reverse' as seen from our perspective, because you'd have to get rid of some entropy, which can't be done.

However, there's no such constraint on entropy. You can - in theory - put energy back if you take it away, and vice versa - there's no explicit law that restricts the 'direction' of energy flow. Energy can be constrained by means of entropic variation - and almost always is in practice, but that's a property of entropy, not energy.

In other words, because energy has a conservation law, things can 'run in either direction' because you end up with the same amount of stuff as you started with. Entropy isn't conserved and has a law that defines how it changes, so that produces the 'arrow of time' effect.
 
  • #3
Thanks. Formulating the questions is almost as difficult as coming to grips with some of the principles.
I have read that it is a goal of all matter to achieve the lowest energy state possible. When objects move from order to disorder, are they always achieving this goal?
 
  • #4
shaun11 said:
Thanks. Formulating the questions is almost as difficult as coming to grips with some of the principles.
I have read that it is a goal of all matter to achieve the lowest energy state possible. When objects move from order to disorder, are they always achieving this goal?

There is no such thing as order and disorder. Precisley, such concepts might exist in philosophy. Terms which would match 'order' and 'disorder' in physics could be 'equilibrium' (with zero velocity) and 'motion'.
 
  • #5
radou said:
There is no such thing as order and disorder. Precisley, such concepts might exist in philosophy. Terms which would match 'order' and 'disorder' in physics could be 'equilibrium' (with zero velocity) and 'motion'.
I have heard the terms "order and disorder" mentioned when regarding the universe. Is the universe (that most people think is expanding) moving from a more ordered situation to a more disordered one or the other way round. The terms order / disorder form part of the entropy priciples, where combined with probability, eggs for example are more likely to break than unbreak (order/disorder). Maybe I am barking up the wrong tree, and need further expanation. My original question was that time "seems" is perceived to move in a certain direction even if Einstein and Newton´s equations do not stipulate this and maintain that in physics, time, as per their theories, can move forward or backward.
 
  • #6
radou is right about the use of order and disorder. We may look at quantities like radial distribution functions when systems undero phase transistion but these have been shown to be pretty poor indicators of phase, just look at the whole class of amorphous solids.

Also matter does not try to minimise its energy if it is not in equilibrium. Classically what is minimised is the action. For time independent systems this correspondes to minimisation of energy.

There is no evidence for a time-reversal symmetry, just as there is no evidence for tachyons. All symmetries in physics do not have to be realized, but we should ask that if they are not, then Why?
 
  • #7
shaun: time doesn't actually "seem" to move in any direction. There's no forward or backward about it. That's just linguistic baggage, what you've been brought up with, what you're used to. What's really happening here is that things move, not time. Time is the measure of this motion against other things in motion, including our clocks, or the workings of our brain.
 

1. What is the concept of the "Time Arrow" in relation to entropy and energy?

The "Time Arrow" refers to the observed direction in which time flows, from past to future. It is connected to the concepts of entropy and energy in that the increase of entropy (disorder) and decrease of energy are both irreversible processes that contribute to the direction of the Time Arrow.

2. How does entropy relate to the Second Law of Thermodynamics?

The Second Law of Thermodynamics states that in any closed system, the total entropy will always increase over time. Entropy can be thought of as a measure of the disorder or randomness within a system. As the Second Law of Thermodynamics states, this disorder will always increase, contributing to the direction of the Time Arrow.

3. What is the connection between entropy and the concept of time itself?

Entropy can be seen as a measure of the progression of time. As time passes, entropy increases, contributing to the direction of the Time Arrow. This can be observed in everyday life, such as the decay of objects or the aging process of living organisms.

4. How does the concept of energy tie into the Time Arrow?

Energy is closely tied to the concept of the Time Arrow, as the decrease of energy is an irreversible process that contributes to the direction of time. The transfer and transformation of energy can also be observed to follow the direction of the Time Arrow.

5. Can the Time Arrow ever be reversed?

Currently, there is no known way to reverse the direction of the Time Arrow. The laws of physics, particularly the Second Law of Thermodynamics, suggest that the increase of entropy and decrease of energy make the reversal of the Time Arrow impossible. However, there are ongoing studies and theories exploring the possibility of reversing time, such as through time travel or the concept of a "big crunch" in the universe.

Similar threads

Replies
14
Views
1K
Replies
9
Views
2K
  • Other Physics Topics
Replies
14
Views
3K
  • Quantum Physics
Replies
1
Views
657
Replies
3
Views
789
Replies
27
Views
3K
  • Astronomy and Astrophysics
Replies
1
Views
1K
  • Quantum Physics
2
Replies
39
Views
5K
Replies
51
Views
3K
Replies
13
Views
1K
Back
Top