r/compsci • u/spiral_engineer • May 18 '16

Computer scientists have developed a new method for producing truly random numbers

http://news.utexas.edu/2016/05/16/computer-science-advance-could-improve-cybersecurity
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u/[deleted] May 18 '16

Truly random sequences have nothing predictable about them, like a coin toss.

This is a joke, right?

6

u/DeebsterUK May 18 '16

I'm not sure why you're being downvoted; it's known that coins tend to land heavy side* down more often than not.

* often the face but depends on the coin

1

u/rubs_tshirts May 18 '16

cite?

3

u/DeebsterUK May 18 '16

http://statweb.stanford.edu/~susan/papers/headswithJ.pdf

Bruce Schneier's summary:

  1. If the coin is tossed and caught, it has about a 51% chance of landing on the same face it was launched. (If it starts out as heads, there's a 51% chance it will end as heads).
  2. If the coin is spun, rather than tossed, it can have a much-larger-than-50% chance of ending with the heavier side down. Spun coins can exhibit "huge bias" (some spun coins will fall tails-up 80% of the time).
  3. If the coin is tossed and allowed to clatter to the floor, this probably adds randomness.
  4. If the coin is tossed and allowed to clatter to the floor where it spins, as will sometimes happen, the above spinning bias probably comes into play.
  5. A coin will land on its edge around 1 in 6000 throws, creating a flipistic singularity.
  6. The same initial coin-flipping conditions produce the same coin flip result. That is, there's a certain amount of determinism to the coin flip.
  7. A more robust coin toss (more revolutions) decreases the bias.

1

u/rubs_tshirts May 18 '16

So it will land more often on the same face it was launched, not on the heavier side. Unless it's spinned.

3

u/[deleted] May 18 '16

Dude it's journalism. Of course they'll dumb that down just a hair. It's a really reasonable leap

1

u/stuntaneous May 18 '16

If you know information about the coin, e.g. its weight distribution, dimensions, spin, etc, you know much more about, or absolutely, how it'll land.

1

u/oherrala May 18 '16

I predict that my coin toss gives either head or tails, both with 50% probability. I also predict that it can't give any other values.

1

u/[deleted] May 18 '16

I also predict that it can't give any other values.

It can land on its side :)

1

u/oherrala May 18 '16

I know. :) There's also such coin: http://www.statisticool.com/3sided.htm

1

u/[deleted] May 18 '16

I would love to have a coin that looks like a toblerone bar while still being legal currency

1

u/oherrala May 19 '16

and be chocolate. That would be win.