Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is there anything truly random?

  1. Oct 15, 2012 #1
    Well I just read about whether mind can produce random numbers or not here.
    But that makes me wonder whether anything in this universe is random or not? I haven't yet studied quantum physics but I know that a lot in it is based on probability.

    So is anything truly random in this universe? Also lately I am wondering about whether we live in a deterministic world or not? Whether something is truly random or not seems related to it.
    Do we have answers to such questions or are we still searching?
  2. jcsd
  3. Oct 15, 2012 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Even if we do live in a deterministic world, a principle of quantum physics shows us that we cannot know all information about our world to perfect precision. Basic chaos theory will then take over to show that without perfect knowledge of our present "initial conditions," the future will be utterly unpredictable.

    Add to the top of that indeterminable pile the probabilistic nature of fundamental particles, where the outcome of any atomic decay, etc, is truly unknowable, and you have, essentially a future that cannot be written, plotted or calculated.

    Any speculation on whether we could predetermine random occurrences are just that, speculation. Basically a game of "OK, so we can't; but what if we could?"

    If atomic decays, etc, can be shown to follow a predetermined outcome (which we currently believe is not the case, and I have no idea how we could prove that, but I'm not the PhD here) then I'd say there was a case for it.
  4. Oct 15, 2012 #3
    If you toss a coin 1000 times, you'd get an approximately 50/50 distribution of heads/tails, so yes, it seems the randomness is genuine.
  5. Oct 15, 2012 #4
    Half of the pages in a book are odd numbered, and the other half are even numbered. So the pages of the book are randomly numbered.
  6. Oct 15, 2012 #5
    The pages are exactly 50/50 distribution, the coin toss is approximately 50/50 and involves radondmness(or unpredictability). Only a conspiracy can 'explain' the approximately 50/50 distribution of thousands of trials(if true randomness were false) and we know conspiracies are very often wrong and not quite inline with known science.
  7. Oct 15, 2012 #6
    Yeah but doesn't the head or tale depend on the force with which we toss. So if we toss with the same force each time and we know all the factors that are acting upon it we can calculate whether it will be head or tale at each toss. So not really random
  8. Oct 15, 2012 #7

    No, i meant something different. Throw the coin against the wall so it hits it and lands afterwards. You can't beat the odds, there is no way around this. There is a whole multi billion dollar entertainment industry exploiting this basic physics phenomenon. The longer you play at a casino the less your odds of winning(in the long run you are always broke).

    As for the conspiracy, Occam's razor is usually enough to dispell it.
  9. Oct 15, 2012 #8
    Sometimes the pages are exactly 50/50, and sometimes not. It is approximately 50/50. Sometimes the coin toss comes out 50/50 and sometimes not. It is approximately 50/50.
  10. Oct 15, 2012 #9

    I don't understand what you are saying, but in true randomness(as is always assumed in the sciences, also called 'naturalism'), the odds of heads or tails is approximately 50/50 and with the increase in number of trials the odds converge to 50/50.
  11. Oct 15, 2012 #10
    January 1st lands on a Monday 1/7 of the time, on Tuesday 1/7, etc. Does this mean that the day January 1st lands on is random? Your description of the coin toss is the same. When you say it comes up heads 1/2 of the time and tails 1/2 of the time, you are merely stating that the distribution is uniform. Randomness is something more. For example, you would also have to prove that the four outcomes hh, ht, th, tt each come out 1/4 of the time and that hhh, hht ... ad infinitum. You could never satisfy yourself that the outcomes were random with only a finite number of tosses. It's even in your own statement about convergence. How can you be sure of convergence with only finitely many tosses?
    Last edited: Oct 15, 2012
  12. Oct 15, 2012 #11

    No because there is nothing unpredictable in the sequence of days. The sequence of days is orderly, the heads/tails distribution is not(only as a large ensemble of trials). This is exactly what you would expect of a truly random(unmediated) event.

    Yes, it's uniform IN THE LONG RUN(!), but not in the short(!). This is a cruicial point that you seem to be missing.

    Because we've been using this assumption all the time and the observations have been confirming it day after day over thousands of years. Do you believe that casinos could lose large sums of money because they have only been able to test randomness with only a finite number of roulette spins? And say for 1 full year the ball could land on red 75% of the time?
    Last edited: Oct 15, 2012
  13. Oct 15, 2012 #12
    I googled
    is a coin toss truly random
    without quotes. I suggest you try it.
  14. Oct 15, 2012 #13
    Listen to Maui. The short run is the important factor. You flip a coin and know much less about what will happen next than what will happen 1,000 times. Randomness is about not being able to predict the elements of the sequence not long term trends. You can easily guess 50% are heads but will it be hhttttthhhhhththhhtttt?
  15. Oct 15, 2012 #14
    Yes Avichal, by assumption.
  16. Oct 15, 2012 #15

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    The randomness of the coin toss comes from the impossibility to perfectly replicate the initial conditions of the toss. If a machine, carefully calibrated, tossed the coin with an identical initial force, in precisely the same location, causing exactly the same rotation, and landing spot, then the toss could be repeated with predictable results.

    But humans are not capable of repeating such precise initial conditions, so the variation of rotation, trajectory, position of edge when it hits etc are what make the outcome unpredictable, or "random."

    The machine I mentioned would need to be of ultra high precision and ultra-slim tolerance just to predict coin tosses, and even then would be unlikely to achieve 100 %.

    The rest of the universe is much more intricately interdependent on "initial conditions."

    Correct me if I am wrong, but Jimmy's point may be that "random" requires a definition. Random is as random does. Take care how we define it.
  17. Oct 15, 2012 #16
    I think that a lot of times something can appear to be random from a certain perspective, even though it is probably not random.

    For instance, when I am walking down the street and I look at people, the directions in which they are walking are pretty much random since I don't know anything about them or where they are going.

    Of course, it's not random at all: each person (probably) has a very specific place to which they are headed. But from my perspective they might as well be a bunch of molecules in a MB distribution.
  18. Oct 15, 2012 #17
    At any rate, randomness is not simply a matter of uniform distribution as indicated in post #3.
  19. Oct 16, 2012 #18
    Is "randomness" a measure of your success/failure rate in predicting what the state of a system will be at a specific future time?

    Is a coin toss only 50% random if you always guess heads next?

    Random is the deviation from expectation.

    The trend of 50% heads is not random. It is what you expect and what you can predict for many coin tosses. The next state, H or T, is random.
  20. Oct 16, 2012 #19


    User Avatar
    Gold Member

    There are three definitions of random that we encounter.

    1) The "laymen"/social version: "Well, that was random!"
    This is basically equivalent to unexpected or out of the ordinary

    2) There's a vague notion of random being used as an opposite to deterministic. If a process is truly "random" in this usage, it seems to indicate a lack of deterministic causality in a system. I.e. probabilistic (like quantum wave collapse when measuring).

    3) Mathematical definition from Wolfram Alpha:


    But your question casts doubt on "true" randomness (in the case of 2), I think, is what you mean). Which, I think, is founded in many cases. Sometimes we have deterministic systems, but they're chaotic and complex, so we just take them to be random when we model them. For instance, noise in a signal we may model with a random function on the computer, but if we were studying noise we may also have a deterministic way of modeling it. If we're measuring signal, we don't care how the noise came about, so the random model is sufficient.
  21. Oct 16, 2012 #20
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook