# What is entropy **URL:** \ **Category:** Factual Questions\ **Created:** [August 30, 2003, 3:41pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643 "2003-08-30T15:41:57Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Sacroiliac](https://avatars.discourse-cdn.com/v4/letter/s/ecb155/32.png) [@Sacroiliac](https://boards.straightdope.com/u/Sacroiliac)\ **Post date:** [August 30, 2003, 3:41pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643/1 "2003-08-30T15:41:57Z")
I think I understand entropy from a statistical mechanics frame but I’m having trouble understanding it thermodynamically. I know it equals the integral of dQ/dT but that leaves me intuitively very cold. Disorder and the arrow of time also leaves me at a pretty low T. You can measure temperature, pressure, and volume can you measure entropy? If you have two containers one at a high temperature and one at a low temperature and you put a turbine between them you can turn the turbine, do work and the entropy increases. What if you connect the containers directly with no turbine in between? ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [August 30, 2003, 3:56pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643/2 "2003-08-30T15:56:11Z")
If you connect two containers they will go to thermal equilibrium and the entropy of the new larger systenm will be greater than the combined entropy of the orginal two containers. ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [August 30, 2003, 6:22pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643/3 "2003-08-30T18:22:47Z")
Listen and Learn: Entropy ---
**Author:** ![robcaro](https://avatars.discourse-cdn.com/v4/letter/r/df705f/32.png) [@robcaro](https://boards.straightdope.com/u/robcaro)\ **Post date:** [August 30, 2003, 8:48pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643/4 "2003-08-30T20:48:30Z")
American Heritage Dictionary defines it thusly: en·tro·py … n., pl. en·tro·pies. 1. Symbol S For a closed thermodynamic system, a quantitative measure of the amount of thermal energy not available to do work. 2. A measure of the disorder or randomness in a closed system. 3. A measure of the loss of information in a transmitted message. 4. A hypothetical tendency for all matter and energy in the universe to evolve toward a state of inert uniformity. 5. Inevitable and steady deterioration of a system or society. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [August 30, 2003, 8:54pm UTC](https://boards.straightdope.com/t/what-is-entropy/198643/5 "2003-08-30T20:54:03Z")
Basically entropy is how sydtems tend to a state of thermal equilibrium. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [August 31, 2003, 10:52am UTC](https://boards.straightdope.com/t/what-is-entropy/198643/6 "2003-08-31T10:52:13Z")
Information and matter (and energy) are different faces of the same underlying stuff. There’s, I forget, 10^60 or 10^80 or so bits per kilogram. The number of bits of information you can fit into a volume is limited to 1/4 of the bounding area in Planck areas (it’s proportional to bounding area instead of volume for general relativistic reasons associated with the mass of the information warping the space it occupies). The biggest clue most of us have heard of is that there are information and energy versions of entropy, which are actually the same thing. See recent Scientific American “Are you a hologram…” article. For my part, I think the untold story is that c is the limiting velocity that information/energy/matter can propagate (too bad history has emphasized “speed of light”, whereas light is only an example of something with information/energy/matter that reaches that limiting speed).