Wikipedia:Reference desk/Archives/Science/2019 February 9

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February 9

Arrow of Time

Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics? 42.61.113.178 (talk) 05:50, 9 February 2019 (UTC)

• Define "low entropy". All the second law requires is that the past has lower entropy than the future. Tigraan^{Click here to contact me} 10:40, 9 February 2019 (UTC)

The Arrow of time concept developed by Arthur Eddington posits that in an isolated system, free energy that can make physical change (i.e. "do work") can only decrease, which is quantified as an inevitable increase in entropy. The Second law of thermodynamics was an empirical confirmation that the total entropy of natural processes can never decrease over time, and it seems to explain the difference between moving forward and backwards in time, such as why the cause precedes the effect (the causal arrow of time). Truesdell, C. wrote ref : "Clausius is the author of the sibyllic utterance, "The energy of the universe is constant; the entropy of the universe tends to a maximum." The objectives of continuum thermomechanics stop far short of explaining the "universe", but within that theory we may easily derive an explicit statement in some ways reminiscent of Clausius, but referring only to a modest object: an isolated body of finite size." DroneB (talk) 16:55, 9 February 2019 (UTC)

That view is controversial. See Wikipedia:Reference desk/Archives/Miscellaneous/2017 February 10#Understanding the solution to Loschmidt's paradox. 2A00:23C0:7983:8301:10E9:F80:9F3F:2269 (talk) 19:28, 9 February 2019 (UTC)

Take a look also at Entropy (arrow of time) where your question is claimed to be an unsolved problems in physics. So do not expect us to be able to give an answer. Graeme Bartlett (talk) 11:21, 10 February 2019 (UTC)

Can some people never do backflips, front flips, or handstands?

Wikipedia articles doesn't say if there's a % of the population that can or can't do, or what's average. I'm a skinny underweight guy, was able to run a mile in 6:30, but could never do any of the 3 my whole life. But yet, I see videos on YouTube of kids even younger than elementary school doing backflips. So is this something that's genetic? Can some skinny-fit people just can't learn? The only thing I can do... is cartwheels. 67.175.224.138 (talk) 17:48, 9 February 2019 (UTC).

I wonder if you could after being trained by a gymnastics coach. --Guy Macon (talk) 18:10, 9 February 2019 (UTC)

I am also naturally motion-sickness (cannot read in moving vehicle). I can overcome it, but eventually lose it after a certain period of time. So I wonder if motion sickness and not being able to do a hand-stand are intertwined. 67.175.224.138 (talk) 04:16, 10 February 2019 (UTC).

I could do nothing the least bit acrobatic except front summersaults. But when I took judo in college, the instructor was so charismatic, one could hardly say no. He also had said that if we did not follow his directions, he would demonstrate every known throw on us until we dropped the class. He said “Do a forward midair summersault.” I said I didn’t think I could, thinking privately that I would break my neck when I landed. He said “Oh, of course not. You need more distance to make the flip. And if you extend your right arm, you will not break your neck.” And he had two students bend over for me to jump over them. I jumped, flipped extended my arm and landed perfectly. He then added another student and another, so I did the flip over four. I felt like I was ready for the circus! It has given me more self confidence for the rest of my life. Edison (talk) 20:12, 9 February 2019 (UTC)

There are always certain exercises that look like way beyond the capability of what you can do. If you can do handstands, you may not be able to do handstand push ups. If you can do handstand push ups, you may not be able to do planche push ups. If you can do planche pushups, you may not be able to do handstand planche push ups. Count Iblis (talk) 21:33, 9 February 2019 (UTC)

This can all be trained, however it becomes increasingly difficult with lake of movement (couch potato state) and age.

Anyway i was the first in my line and so lucky to get a chance to get to know my Great Granddad. And he, with his 96 years, demanded to show me a solid Headstand, against much protest of the rest of the Family. So you just have to beat your inner "Schweinehund" and keep training. Till you are 96!! One of the best ways may be to start may be to begin your day with Tai Chi. --Kharon (talk) 13:47, 10 February 2019 (UTC)

The OP would be well-advised to read "You Are Old, Father William". ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:22, 10 February 2019 (UTC)

Human urine by gender.

Wikipedia article doesn't talk about urine by gender, but I was wondering if anyone can bring a list of cases that may be able to differentiate human urine by gender. 1 is I heard that male urine may have more testosterone vs. estrogen, and another is certain bacteria may show up in female urine only. Obviously, these are not absolute cases. 67.175.224.138 (talk) 17:55, 9 February 2019 (UTC).

I've heard that females dogs' urine kills grass in lawns, but male dogs' urine doesn't. Abductive (reasoning) 19:23, 9 February 2019 (UTC)

Urination#Dog-like_mammals_(Canidae) (NSFW) covers some difference that would be use of vertical surfaces more so by males, but the impact is due to behaviour. However The OP is probably more interested in the actual content of urine. Graeme Bartlett (talk) 11:04, 10 February 2019 (UTC)

No, it's due to the hormones in female dog urine, you didn't bother actually looking it up. Abductive (reasoning) 04:58, 11 February 2019 (UTC)

There have been several studies which did find some differences in male and female urine: [1], [2], [3]. Brandmeister^talk 14:19, 10 February 2019 (UTC)

Chinese boiled eggs, anyone? Martinevans123 (talk) 22:14, 10 February 2019 (UTC)

The presence of some chemicals in urine is used to detect pregnancy, implying that such presence indicates gender (although the absence of it does not). Mitch Ames (talk) 11:19, 11 February 2019 (UTC)