Tuesday, November 11, 2008

Random-ness? Predicting the future

If I roll a dice, I have equal chances of getting a '6' or a '4'. However, if I have rolled a '6' once, then my second roll has lower chances of getting a '6'.

This is 'cause probability of getting two sixes in a row are low. However, both my rolls were independent rolls. Independently, I should have equal chances of a '6' both times. Then why does this happen?

Also, if 6 different people were to roll six different dice at the same time, theoretically we should get each of the numbers. But that isn't so in reality. Why?

Also, if V were to roll a six and then I were to roll, m probability of a 6 is low.

Can we predict the dice roll on the basis of previous rolls?

Now, let's make it simpler and take a coin; say I will be tossing the coin 3 times and I will have to predict the third toss result. First toss is 50-50 chance and I get a head. Second time , I get a head again. My prediction would then be a tail for the third one. BUT, what if I get a head and then a tail? What should my third guess be then? I would say head because the probability of two tails in a row is low. (But then again, head-tail-head should also be low. )

If I were to know what everyone on earth rolled till date and the number of times a number has been rolled, should I be able to predict the next number?


Going back to the original predict the future question, I don't think we can predict our own future just on probability alone. Example: pick a number between 1-20. Apparently, the most common human-generated-one is this.

4 Comments:

Blogger EntrepreneurNI said...

Thanks Vishwa!

I have emailed you- let's catch up.

November 21, 2008 at 5:15:00 AM EST  
Anonymous Anonymous said...

However, if I have rolled a '6' once, then my second roll has lower chances of getting a '6'.
I know it sounds counter-intuitive (it was at first to me), but no, you're not less likely to roll the second six.

The only way I could get my head around it was to understand that the probability to roll a '6 and 1' or a '6 and 2' is the same as the probability to roll a '6 and a 6'. It's a contorted way to understand IID, but it helped me.

As for the deterministic prediction of the future based on causality and present state, I get the feeling that we've spoken about Laplace's Demon sometime ages ago. If you weren't aware of it, then you've stumbled upon it independently. Kudos!

November 21, 2008 at 2:19:00 PM EST  
Blogger EntrepreneurNI said...

Bipin,
I know what you are teaching me is covered in probability 101. I do understand that these are independent rolls. BUT- together, the chances do go down. I mean, even as indendent rolls, the chances of rolling two 6s or three 6s VERSUS everything else is low. [ P(A).P(B).P(C) ]

And yes, we did speak about it earlier

November 25, 2008 at 1:52:00 AM EST  
Blogger Deepika said...

Subhi, what's you take on astrology?

February 24, 2009 at 1:18:00 AM EST  

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