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Time

Started by irreversible Sep 19, 2006 at 11:54 AM 6 replies 1.5k views

Original Post

irreversible

386

irreversible

Sep 19, 2006 at 11:54 AM

This is not a programming-related question, but a physics-related question. My knowledge in the field is pretty minimal - thus I'm starting this thread. To give everyone a reference point, ponder over this for a couple of seconds (pun intended): "The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." - Wiki source - I've recently started wondering (that's wondering, not thinking or assuming) about the nature of time at very small quanta. Based on something I remember reading somewhere, that said time would essentially lose shape and form at very small quanta and become a kind of "fudge" captivated me. I don't remember where I read this, but apparently it's somewhat difficult to find anything too useful on the Internet. Are there any specific books anyone could recommend for me to read? I don't want anything too mathematical, but rather something along the lines of notes on actual experiments that have been held. Some basic stuff, such as how atomic clocks work, would be nice too. I mean, Wikipedia is okay, but it's still... you know - Wiki. I trust, however, that there's no definitive bible on the subject that would have all the answers, so if you know of any sources at all, please let me know. Why the quote, you might ask. Easy - that's the basis of measuring time today. So it has to be a place to start from. The simple question: why that number of periods? Why not more? And a better question: how many more periods can there be in any given discrete amount of time? The answers, I trust, are more intelligent than the questions, though.

Motorherp

Sep 19, 2006 at 12:31 PM

Quote:
Original post by irreversible
I've recently started wondering (that's wondering, not thinking or assuming) about the nature of time at very small quanta. Based on something I remember reading somewhere, that said time would essentially lose shape and form at very small quanta and become a kind of "fudge" captivated me.

I believe whomever you are quoting was likely referring to Heisenburg's uncertainty principle. unfortunately I cant recommend any books that aren't too mathematical since the only ones I know of which go into this subject in depth are quantum mechanics text books. You could maybe try Lectures on Physics which a friend of mine says is very good without requiring advanced physics or maths knowledge but I dont know if this subject is covered or not.

With regards to why 9,192,631,770 periods were picked, it is simply because this was the closest measure we could get to the pre-physics-standard second using an accurate unchanging system. The original definition of a second came from a division of the rotational period of the Earth (ie: a day) but this is a varying amount and not accurate enough for physics use which is why a new standard was set. At least thats what I think anyway ... makes sense to me.

Verminox

Sep 19, 2006 at 1:30 PM

I'm pretty sure that when people started using the term one second hundreds or possibly thousands of years ago, they did not know how many periods of radiation occured during that interval. Although I am not completlely sure of how one second was defined earlier, I know that the 60 seconds to a minute, 60 seconds to an hour, etc. has something to do with counting in the Sexagesimal number system (base sixty). The new definition only serves as a way to standardize the measurement of time universally by using a quantity that is fixed and constant universally.

irreversible

Author

386

irreversible

Sep 19, 2006 at 2:05 PM

That may be so. However, I'm pretty sure there's plenty of research that's been done in the field. Disregarding the maths, what titles did you have in mind, Motorherp?

PS - Heisenburg's uncertainty principle is what I had in mind - thanks!

WarAmp

Sep 19, 2006 at 2:56 PM

Planck Time and Planck Units

Motorherp

Sep 19, 2006 at 3:00 PM

Indeed there has been plenty of research done in the field. If you really want to pick up a book on the subject I found 'Qunatum Mechanics by Alastair I. M. Rae' to be one of the most comprehensible (sorry I cant find a link). I should warn you its not easy reading though. Without a firm base in physics and mathematics there's a high chance your patience with the subject will expire before you've satisfied your curiosity. There is an excellent section in the back of that book though called 'The Conceptual Problems Of Quantum Mechanics' which covers issues such as Schrodinger's Cat that you might find very interesting without really having to understand any of the underlying maths.

nonoptimalrobot

Sep 19, 2006 at 7:11 PM

Try picking up a copy of the following (in order of difficulty):

The Universe in a Nutshell
A Brief History of Time
The Elegant Universe
The Fabric of the Cosmos

The first two are by Hawking and the second two are by Brian Green. Universe in a Nutshell is basically a picture book but it's a fun read anyway. The Frabric of the Cosmos covers what is in The Elegant Universe plus a bunch of other stuff. I recomend reading them both, Elegant Universe first, as you are likely to mix things up a bit the first time around (I certainly did)

All four discuss quantum mechanics, relativity, and the theory we have yet to discover that will unify the two. In all of this jabbering is of course a great deal about the nature of time and how it behaves on the quantum scale vs how it behaves at the scale where relativity becomes an important factor.

A Brief History of Time is a little dated as some important discoveries have been made since it was published. Keep that in mind while reading

One more thing, none of the books are actually difficult. You'll have to think but you won't have to take notes or scribble down greek letters. What I meant by "order of difficulty" is basically the depth at which the topics are explored.

nilkn

122

nilkn

Sep 19, 2006 at 7:28 PM

Quote:
Original post by irreversible
I don't want anything too mathematical, but rather something along the lines of notes on actual experiments that have been held.

In this case, I definitely second the book suggestions by nonoptimalrobot. Steven Hawking treats the difficult subjects of quantum mechanics, relativity, and others in a very "step-motherly" fashion; his books really are aimed at people who are deeply curious about modern physics, but aren't interested in deciphering pages of arcane equations with greek letters abounding.

I was able to make sense of Hawking's The Universe in a Nutshell way back in sixth grade, so that definitely says a lot about the clarity of the explanations.

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