Understanding Entropy: Exploring the Paradox of Time Travel and the Big Bang

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In summary: more entropy now than it did in the past because it has evolved from a less ordered state to a more ordered state. i think the entropy in the big bang was incredibly low because there was no structure to it.
  • #1
MathematicalPhysicist
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the entropy level (disorder) increase with the time flow (as it the entropy is bigger in the future), so if we would go against the flow of time, time travel to the past then the entropy will decrease my question is if we will go back to the past till the big bang the moment of creation does that mean the entropy is at it's lowest there is relative order to the future now how can that be?
if I am not mistaken the creation of big bang is a thing of disorder isn't it?
 
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  • #2
Are you speaking of the evolution of life or matter?

Nautica
 
  • #3
The direction of increasing entropy is called the "thermodynamic arrow of time" and it is one of the main reasons you can't go back in time.

Now, your question itself is a fairly incoherent run-on sentence, so I'm not exactly sure what you are getting at. But since time and the universe start at the big bang (or rather, at a point in time just after the big bang), there is no "before" with which to measure a change in entropy before and after the big bang.

Overall, I guess you are asking if the big bang theory contradicts the second law of thermodynamics. No, it doesn't.
 
  • #4
The entropy of the universe is thought to have been very low near the beginning of the universe. Nobody can calculate the entropy of the Big Bang itself, since it's a singularity, but there is no reason to assume that it must have been a high-entropy state.
 
  • #5
so it means order has been in the big bang.
to me it's contradictory because in the beginning there wasnt structure to the universe and now there is and as i understood it entropy is another word for disorder now how can it be that in the big bang there was more order than now?
 
  • #6
'Order' is such a vague term, so when applying it to something quantifiable like entropy you have to be precise. Entropy is usually thought of as dS = dq/T, where dS is the change in entropy, dq is the energy absorbed by the system and T is the thermodynamic temperature, but in terms of the Boltzmann entropy theory it can be thought of as the following

S - S0 = k ln(W/W0) ----------------(1)

Where W is the number of microscopically distinct states that give rise to the same macroscopic state of the system (in terms of quantum mechanics this would be the number of solutions to the Schroedinger wave equation giving the same energy distribution), k is the Boltzmann constant, S0 is the entropy of a standard conditon and W0 is the probabilty of a standard condtion.

The third law of thermodynamics state that a perfect crystal at absolute zero has an entropy of zero using this fact and (1) you can then show that any non-perfect molecular configuration has a certain amount of what is known as configurational entropy that is intrinstic to it and this is what can be thought of as disorder. The early stages of the universe by this defintion would be very ordered, infact incredibly so, IIRC the probabilty of the current universe sponateously revrting back to this amount of order would be 10-123.
 
  • #7
Originally posted by loop quantum gravity
to me it's contradictory because in the beginning there wasnt structure to the universe and now there is and as i understood it entropy is another word for disorder now how can it be that in the big bang there was more order than now?

As jcsd, "order" is a vague term. What one intuitively thinks of as "order" doesn't necessarily correspond to "low entropy".

For instance, take a cloud of gas, which gravitationally collapses to form a solar system, with a star, planets, etc. Would you say that the universe is more "ordered" after the formation of the solar system, than it was before? Maybe ... but does it have less entropy? No: it has more entropy. See:

http://groups.google.com/groups?selm=9thcur$6jd$2@woodrow.ucdavis.edu
http://groups.google.com/groups?selm=906b1c$81u$2@mark.ucdavis.edu
http://groups.google.com/groups?selm=aip9kj$bhk$2@woodrow.ucdavis.edu

(These articles are very similar to each other, but they have slightly different references and details, so I cited all three.)
 
  • #8
Originally posted by Ambitwistor
As jcsd, "order" is a vague term. What one intuitively thinks of as "order" doesn't necessarily correspond to "low entropy".

For instance, take a cloud of gas, which gravitationally collapses to form a solar system, with a star, planets, etc. Would you say that the universe is more "ordered" after the formation of the solar system, than it was before? Maybe ... but does it have less entropy? No: it has more entropy. See:

http://groups.google.com/groups?selm=9thcur$6jd$2@woodrow.ucdavis.edu
http://groups.google.com/groups?selm=906b1c$81u$2@mark.ucdavis.edu
http://groups.google.com/groups?selm=aip9kj$bhk$2@woodrow.ucdavis.edu

(These articles are very similar to each other, but they have slightly different references and details, so I cited all three.)
that's what puzzled me too.
the universe has structure and although it is ordered it's entropy is high.
what is the term of "order" in physics? (i thought it was low entropy).
 
  • #9
Originally posted by loop quantum gravity
the universe has structure and although it is ordered it's entropy is high.
what is the term of "order" in physics? (i thought it was low entropy).

As far as I know, there is no mathematical definition of "order" that corresponds in all cases to our intuition.
 
  • #10
Read through the links that Ambitwistor posted, as they explain how in large systems where gravity pre-dominates, as entropy increases so does inhomogenity. The early universe was incredibly homogenous.
 
  • #11
Originally posted by jcsd
Read through the links that Ambitwistor posted, as they explain how in large systems where gravity pre-dominates, as entropy increases so does inhomogenity. The early universe was incredibly homogenous.
also now the universe is homogenous.
if it wasnt then how could you say that the laws of physics apply everywhere in the universe?
 
  • #12
Originally posted by Ambitwistor
As far as I know, there is no mathematical definition of "order" that corresponds in all cases to our intuition.
i think it's more a philosophical question then a mathematical one.
 
  • #13
Originally posted by loop quantum gravity
also now the universe is homogenous.
if it wasnt then how could you say that the laws of physics apply everywhere in the universe?

You are right the universe still is pretty homogenpus, but nowhere near as homogenous (and by homogenopus I mean homogenous in the distribution of it's matter) as it was in it's early stages.
 
  • #14
Originally posted by jcsd
You are right the universe still is pretty homogenpus, but nowhere near as homogenous (and by homogenopus I mean homogenous in the distribution of it's matter) as it was in it's early stages.
becuase the space where the universe just begun was... how should i put it, "small" and now as it's evolving so has matter evolved with space.
 
  • #15
And what has this evolution amounted to in terms of entropy? An increase.
 
  • #16
Originally posted by loop quantum gravity
i think it's more a philosophical question then a mathematical one.

Which brings us to the 4th law --- "It is impossible to do any useful thermodynamic work with a thesaurus." Entropy is a thermodynamic state function defined in the first half of the 19th century. This is prior to the statistical mechanical arguments. Statistical mechanics gives us partition functions for systems; if you must use the stat. mech. approach to analyzing questions involving entropy, WRITE THE PARTITION FUNCTION FOR THE SYSTEM! Don't appeal to the lame, intuitive (and incorrect) analogy that entropy is equivalent to a measure of disorder. And, NEVER take that lame analogy and run with it to the thesaurus --- order=structure=sequence=a thousand other untenable arguments (running with analogies is every bit as dangerous as running with scissors --- you WILL cut yourself).
 

1. What is entropy and how does it relate to time travel?

Entropy is a measure of the disorder or randomness in a system. It is often used to describe the arrow of time, which is the observation that time seems to flow in a specific direction from the past to the future. Time travel, on the other hand, is the concept of moving between different points in time. Entropy and time travel are related in the sense that time travel would require a reversal of entropy, which goes against the laws of thermodynamics. This forms the paradox of time travel - if time travel were possible, it would defy the natural progression of entropy.

2. How does the Big Bang relate to the concept of entropy?

The Big Bang theory is the prevailing scientific explanation for the origins of the universe. It states that the universe began as an incredibly dense and hot singularity, and has been expanding and cooling ever since. The concept of entropy is closely tied to this theory because the universe started in a state of low entropy (high order) and has been increasing in entropy (becoming more disordered) over time. This increase in entropy is what drives the expansion of the universe.

3. Can entropy be reversed and how does this impact our understanding of the arrow of time?

According to the second law of thermodynamics, entropy can only increase or remain constant in a closed system. This means that entropy can never be completely reversed. However, there are instances where entropy can appear to decrease, such as in biological systems or in the formation of stars and galaxies. This does not violate the second law of thermodynamics, as these systems are not completely closed. The arrow of time is still a fundamental concept, as the overall trend of entropy increasing in the universe is always observed.

4. What is the relationship between entropy and information?

Entropy can also be thought of as a measure of information. In information theory, entropy is used to describe the uncertainty or randomness in a message. The higher the entropy, the more uncertain or random the message is. This is because a message with high entropy contains more information than one with low entropy. This relationship between entropy and information is important in understanding how information is processed and transmitted in various systems.

5. How does the concept of entropy help explain the concept of time dilation in relativity?

Time dilation is the phenomenon where time appears to move slower for objects in motion compared to stationary objects. This is a key concept in Einstein's theory of relativity. Entropy plays a role in this by showing how energy and matter interact to create the fabric of spacetime. As objects move, their entropy increases, causing a decrease in their relative energy and mass. This results in time appearing to slow down for the moving object. Entropy also helps explain the concept of the arrow of time in relativity, as the increase in entropy is directly linked to the passage of time.

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