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

50% probability

  1. Jan 27, 2005 #1
    Some people argue that the probability of any event is always 50% .... it either happens or not, regardless of the odds.

    what do u think?
  2. jcsd
  3. Jan 28, 2005 #2

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    That they don't know what probability is. And if they wish, I will happily play them at any gambling game they care to name.
    Last edited: Jan 28, 2005
  4. Jan 28, 2005 #3

    Are they trying to say if I throw a 100 sided dice, it will have a 50% probability of landing on 5?
  5. Jan 28, 2005 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    No Vincent:
    Since the die may either land or not, they're saying it is only a 50% chance of it ever landing..:wink:
  6. Jan 28, 2005 #5


    User Avatar
    Science Advisor
    Homework Helper

    Ahh but isn't there a 50% chance all the molecules will suddenly decide to all go off in different direction before the die leaves your hand? Also what about the 50% chance your hand turns into an iguana and eats the die?
  7. Jan 28, 2005 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    I'll go for the iguana scenario..:biggrin:
  8. Jan 28, 2005 #7
    It might change... that is if we get a "super" computer that can "instantly" compute every single aspect in the universe... and then we can see what other factors are able to change our probability. :biggrin:
  9. Jan 28, 2005 #8
    Moneer81:Some people argue that the probability of any event is always 50% .... it either happens or not, regardless of the odds.

    what do u think?

    Alot of discussions in threads on these forums can delve deeply beyond my highschool education but let me take a crack at this by saying that whether somehting happens or not is completely different than what the odds are of it happening. Those people that make the above statement are formulating an argument I think based on a skewed idea of exactly what a probability or odds are.
  10. Jan 28, 2005 #9
    You'll get better responses in the philosophy forums, methinks.
  11. Feb 1, 2005 #10
    This seems to me like an extended case of a BinomiaL ProbabilitY DistributioN;
    the outcomes are either success or failure, so I can see how people might argue that each has 50% happening.

    Let n=# of trials, and s=the successful/favorable outcome (the one we want). By definition, the "probability" of 's' equals the frequency of 's' in n#trials, as n approaches infinity (we get more and more trials). By law of large numbers, the probability of 's' approaches the theoretical probability of 's', and thus we may not always get the 50% probability for success or failure, if, for example, there are 3 ways to succeed but 7 ways to fail.

    The 50% theory here may also be just a case where, to simulate each outcome (success/failure), we flip a penny. The theoretical probability of success may be, for example, 3/7, but we may get 50% if we flip a penny to determine success/failure---rather than a 10-sided die with 3 faces for success and 7 for failure.

    We can argue 50% probability for outcomes which either happen or don't happen, but only if each such outcome has equal likelihood of occuring, because 50%chance success means 50%chace failure as well.

    In my opinion, by philosophy, we do not "know" exactly what each subsequent outcome will be in the course of an experiment (with binomial outcomes), for example; we can only guess and make calculations as to which is more "probable". However, theoretical probability cannot 100% predict the outcome of the next trial (it can guess, but not with 100% accuracy!) (It seems nature takes its own course ). Because we are not completely "sure" of outcomes in upcoming trials, people might argue that we cannot really use theoretical probability at all to exactly predict the next outcome, and only assume that just 'cause there are only two outcomes with an uncertain "exact" probability, we cannot use theoretical probability at all (because it's not exact!)! Thus, we are left only to assume that each outcome has 50% occuring, because we are "equally-unsure" of the exact chance of failure and the exact chance of success!

    (Well, what do you guys think :redface: ? I understand the viewpoint of people who argue 50%-50%chance theory (or whatever it is called), but i don't think "probability" is really the best word to describe this position)

    But then i think...suppose we could develop such a computer! =>if we analyze every possible variable...down to the smallest particle..."exactly"----would it actually turn out that, down to this smallest level of influence...the probability of influence will actually be 50%-50% (either "influence" or "no influence" binomial outcome)? (by "smallest influential variable"...i mean even the "stuff" that exist in the beginning of time that influenced..then influenced....then influenced...(well, you get the point)..everything up until present)? (to make things easier, assuming that only a single variable is under examination...which influenced everything else, and was not influenced at all by anything which came before it---)

    You know the saying that goes, "We do know anything for certain..."; well, i wonder if this might apply to this 50%-50% probability idea. According to this saying (and not taking into account probability, which is uncertain!), can we be certain at least that we have exactly equal uncertainty for any event? If so, then binomially, then the 50%-50% theory makes some sense. The central idea here is that we are either 100% certain about the event, or uncertain (i.e., 0% certain) about it; what do YOU think?

    I think this should be in the philosophy post/section.
    Last edited: Feb 1, 2005
  12. Feb 6, 2005 #11
    probability does not equal frequency....
  13. Feb 6, 2005 #12
    well of course--i meant the "proportion of 's' in n#trials, as n goes to infinity"
    But what do you think of the rest of the post?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook