Chetan's web scribblings! » Science

You cannot get everything! Specially, out of distributed system!

Chetan — Fri, 26 Mar 2010 05:52:09 +0000

CAP theorem (Brewer’s theorem) :
It is impossible for distributed computer system to simultaneously provide all three of the following guarantees:

Consistency: There are many way to describe it
* All nodes see the same data at the same time.
* Once a state is stored in the system, it will report the same state in every subsequent operation until the state is explicitly changed by something outside the system.
* A service that is consistent operates fully or not at all.
* In other way to say, atomic-ness is built-in to service.
Availability:
* The degree to which a system is operable and in a committable state at the start of a mission, when the mission is called for at random
* Node failures do not prevent survivors from continuing to operate
Partition Tolerance:
* The system continues to operate despite arbitrary message loss
* No set of failures less than total network failure is allowed to cause the system to respond incorrectly

In other words, though it is very desirable to have Consistency, Availability and Partition-tolerance in distributed system, unfortunately
no distributed system can achieve all three at the same time!

Pity!

Universe as a computation device!

Chetan — Wed, 24 Mar 2010 07:37:19 +0000

Here is quote from paper published by Seth Lloyd of MIT in 2001.

“Merely by existing, all physical systems register information. And by evolving dynamically in time, they transform and process that information. The laws of physics determine the amount of information that a physical system can register (number of bits) and the number of elementary logic operations that a system can perform (number of ops). The universe is a physical system. This paper quantifies the amount of information that the universe can register and the number of elementary operations that it can have performed over its history. The universe can have performed no more than 10^120 ops on 10^90 bits.”

Enjoy!

Accidental ideas are valueable, too! do not ignore them!

Chetan — Tue, 20 May 2008 08:40:18 +0000

To prove, here is partial list of useful things produced, discovered or invented by accidental idea(s):

1. Microwave Oven
2. Pacemaker
3. Velcro
4. Slinky (Spring like toy)
5. Saran Wrap
6. Safety Glass
7. Urea Synthesis
8. Teflon
9. Super Glue
10. Scotch Guard
11. Helium
12. Iodine
13. Polycarbonates
14. Celluloid
15. Rayon
16. Indigo
17. Saccharin, Aspartame, Acesulfame – sweeteners
18. Penicillin
19. LSD
20. Viagra
21. Laughing Gas
22. Oral contraceptive
23. Vaccination
24. Uranus
25. Superconductivity
26. X Rays
27. Inkjet printer’s working principle
28. Rubber Vulcanization
29. Corn Flakes
30. Ice Cream Candy Bar
31. Post-It Notes
32. Potato Chips
33. Frisbee
34. Sandwich
35. Coca-cola
36. Champagne

Toss a coin

Chetan — Mon, 16 Jan 2006 12:24:00 +0000

Q: “If you toss a coin a thousand times, how often will it
come up heads?”

A: “About fifty percent of the time.”

If you consider this as “truth”, check http://www.npr.org/templates/story/story.php?storyId=1697475.

Real problem is how to evaluate actual situations (force, friction, airflow, weight etc) and calculate, without error, using scientific rules to find out if coil will come head up or tail up. If one assumes that actual situation and calculation is possible then “50%” becomes absurd. I do not know if it is possible or impossible to know actual situation physically or in principle.

There are more subtle things to note.

We are talking about throwing coin up then it comes back. We catch it or let it hit ground and get settled. We are NOT talking about throwing coin sideways. We are NOT talking about throwing coin straight into sandy ground in a way that it does not roll and will have head up.
We are talking about throwing coin near a large body with enough gravitational force so that coin actually comes back with enough speed to hit the solid ground and roll. If you throw coin in outer space void of enough gravity, it will not come back.
We are NOT talking about ground which is sandy (not solid), where coin can even stand submerged in sand.
We are also assuming that we will decide when coin comes at rest within reasonable period of time. Once coin settles, we do not wait till next tsunami to arrive to change position of coin.
We are talking about fair coin. Coin is designed in a way that no side is favored to drop up. Is it possible to manufacture such a coin? Not today.
We think that GOD (I do not know what ‘GOD’ means) is fair and does not favor any side to drop up.

Put your comments if you can make this list longer…

Have fun.