Is there inherent, observable randomness in the universe?

[Siegmund]

Even if you don't care for the Copenhagen interpretation, radioactive decay still appears to be a completely random process.

It has a characteristic rate for a given isotope - but beyond that, we are completely unable to predict in advance when a given atom will decay, and completely unable to influence that rate of decay. Maybe we just aren't able to look in the right place, to "see what time the fuse is set for?" No. The distribution of decay times is exponential; each atom has no memory at all of its past, just as likely to decompose its first minute whether it was freshly made in a reactor or has been around since before the formation of the earth.

[kevyk]

Hi Chez,

It has been a while since I studied this, but I don't believe that the Bell experiments inherently mean "there is no hidden variable or the speed of light can be exceeded." I believe that the results indicate that both are true.

First, consider the result that says before the measurement the particle's spin is indeterminate. I believe that this is a function of the fact that when the particle's spin is measured, it is with respect to a random set of axes. If the particle had a definite spin, it would spin about a definite axis. This would produce a quantifiable disparity in the number of times you counted it as "spin-up" vs. "spin-down" as opposed to a particle which is forced to decide by your measurement what axis it is spinning with respect to.

The experiments also uphold the quantum-mechanical prediction that entangled particles instantly "know" whether the other has been measured. Measurements of entangled particle B reveal that it knows A is "spin-up" before a light signal relaying that information could have arrived.

Most physicists get around this seeming violation of general relativity by noting that no information actually traveled faster than light. After all, the two spin-measurers don't know that locality has been violated until they can get together and compare notes--neither initially knows who made the first measurement.

Also, it's useful to note that some things (never physical objects) are known to move faster than light. An example: place a lamp in the middle of the universe, then move a shade across it at any speed. The shade will block a certain amount of visual angle per time, which means that if you move far enough away from the light, the edge of the shadow produced will be moving at faster than c. The point is, shadows aren't real things, so it doesn't mean much when they seemingly violate special relativity.

There are several nonlocal hidden-variable die hards out there, but it's my impression that they have to use pretty fanciful contortions to make their theories match experiment. I will look back over my old textbooks to see if I'm forgetting something, but that will have to wait until tomorrow evening (they're halfway across town at my parents' house).

Later,
Kevin

[Darryl_P]

[ QUOTE ]
Even if you don't care for the Copenhagen interpretation, radioactive decay still appears to be a completely random process.


[/ QUOTE ]

This is very interesting and looks to be a strong argument, but to me it again simply shows our own limitations, ie. our lack of understanding of what causes radioactive decay.

A weakening factor is that, unlike the uncertainty principle which claims we can NEVER know the position of certain particles, this example only shows that we DON'T AT THE MOMENT know what causes a particular atom to decay.

In my limited browsing I found this experiment which shows that one type of decay may be caused by neutrinos, an assertion which, if true, would suggest that the seemingly random behavior of decaying atoms is only pseudo-random.

It also makes this statement:

"In contemporary physics, it is well-known and widely accepted that radioactive decay is governed by quantum-mechanical tunnel effects"

which I don't really understand, but if it's *governed* by QM, then doesn't its determinism/randomness depend on QM's determinism/randomness?

[Darryl_P]

[ QUOTE ]
Regardless, whether the physical laws are ultimately deterministic or nondeterministic has nothing at all to do with whether "god" exists. Presumably, this "god" could have "designed" the universe to be nondeterministic. (In fact, some theists argue precisely that to rectify the contradiction between on omniscient god and free will.)


[/ QUOTE ]

I agree that inherent randomness would not *prove* the non-existence of God, just as verification of a miracle would not prove God's existence. I didn't mean to claim that, though, only that my own belief system depends heavily on it. My reason for creating this thread is to find out more about determinism vs. randomness and not to try to convince anyone that my belief system is good or correct.

Having said that, I've noticed a lot of atheists rely on the ultimacy of randomness, though, and so if that were weakened, their beliefs could be weakened as well.

[David Sklansky]

"It has a characteristic rate for a given isotope"

Do we know what causes that rate?

[ QUOTE ]
I've noticed a lot of atheists rely on the ultimacy of randomness,

[/ QUOTE ]

No, you've seen a lot of theists argue against the ultimacy of randomness. But I have not read any atheist "rely on it", since they are not the ones making any broad-brushed claims (see theists) to need shaky foundations to rely upon.

[chezlaw]

Hi Kevin

Thanks for the thoughful reply. I'n not pushing any non-local agenda here and I'm well beyong my knowledge of QM and relativity.

However, QM and some of its wierder phenomena remind me strongly of something else that is compatible with classical physics, an efficient computer program that simulates a classical universe. [I'm not saying there is any reason to believe thats what going on but if my idea has merit then it means there must be a way of making QM, relativity and determinism consistent which need not involve a computer simulation].

The specific points you raise:
[ QUOTE ]
This would produce a quantifiable disparity in the number of times you counted it as "spin-up" vs. "spin-down" as opposed to a particle which is forced to decide by your measurement what axis it is spinning with respect to.

[/ QUOTE ]
The 'forced to decide by your measurement' is exactly how an efficient simulation would work. No efficient program would calculate values until they are needed. While all thats needed is the probability function then stick with that, when a value is required then collapse the probability function into a value using a deterministic pseudo-rnd. [it must be best to work this way as most of the time the value is never measured]


[ QUOTE ]
The experiments also uphold the quantum-mechanical prediction that entangled particles instantly "know" whether the other has been measured. Measurements of entangled particle B reveal that it knows A is "spin-up" before a light signal relaying that information could
have arrived.

[/ QUOTE ]
In the simulation this is easily understood. The up and down spins are entangled in a probability function but A must be up and B down (or vice verca) when/if they are given values.

Once the up/down of A is forced to be given a value (measured) then the up/down of B is forced to be given the opposite value at the same time, the same time being as fast as the computer can do it. This is necessarily many orders of magnitudes faster than the speed of light within the simulation, which gives the appearance of instant action at a distance.

Its a fanciful idea that came to me when I was working on some artificial life simulations. For efficiancy reasons, a just in time evaluation of values is almost neccesary. It also makes sense to impose a speed limit within the system which prevents a simple newtonian model.

Fanciful idea that floats or a dead duck?

chez

[kevyk]

[ QUOTE ]
No efficient program would calculate values until they are needed.[it must be best to work this way as most of the time the value is never measured]


[/ QUOTE ]

This is pretty much how the the equations of QM work. A particle's quantum state is represented by a probability density function (psi) in either position or momentum space. Psi can be represented as a vector in an infinite-dimensional Hilbert space, because all psi's are orthogonal to each other. "Measurements" are represented in this theoretical framework by non-commuting operators which return an eigenstate of psi. The fact that the operators don't commute (meaning that first operating on psi with the position operator, then with the momentum operator gives different results than the reverse) is in some sense the guts of QM.

Most interesting problems in QM involve particles or systems of particles which are in a superposition of quantum states, where psi = a*psi1 + b*psi2 + ..., in which case the probability of measuring the particle to be in state psi1 is a^2/(a+b+...)^2.

Where I think you go wrong is in saying that there's something deterministic going on in the measurement process. While you could be right, there's no evidence to support this, and QM works just fine without it.

You sound like you know probability and linear algebra pretty well--a book in introductory QM might be acessible to you. H.J. Griffiths has written a pretty good one.

[BruceZ]

[ QUOTE ]
"It has a characteristic rate for a given isotope"

Do we know what causes that rate?

[/ QUOTE ]

For alpha decay, the energy of the emitted alpha particle determines the probability that it can escape the strong electromagnetic attraction of the nucleus via a quantum mechanical phenomenon called barrier penetration. For different nuclei, the decay energy of the alpha particle varies so greatly that it causes the rate of decay to range over 24 orders of magnitude, from 2 million decays per second for Polonium 212 to over 10^18 seconds per decay for Uranium 238.

The total energy of the emitted alpha particle (4 - 9 MeV) is always much less than the nucleus' barrier potential (~30 Mev). The fact that the alpha particle can escape at all can only be understood as a quantum probabilistic phenomenon, whereby the particle’s wave function psi penetrates through the barrier region where classically the particle would not be allowed, and then affords the particle a non-zero probability of popping out on the other side.

[Trantor]

[ QUOTE ]
[ QUOTE ]
Even if you don't care for the Copenhagen interpretation, radioactive decay still appears to be a completely random process.


[/ QUOTE ]

This is very interesting and looks to be a strong argument, but to me it again simply shows our own limitations, ie. our lack of understanding of what causes radioactive decay.

A weakening factor is that, unlike the uncertainty principle which claims we can NEVER know the position of certain particles, this example only shows that we DON'T AT THE MOMENT know what causes a particular atom to decay.

In my limited browsing I found this experiment which shows that one type of decay may be caused by neutrinos, an assertion which, if true, would suggest that the seemingly random behavior of decaying atoms is only pseudo-random.

It also makes this statement:

"In contemporary physics, it is well-known and widely accepted that radioactive decay is governed by quantum-mechanical tunnel effects"

which I don't really understand, but if it's *governed* by QM, then doesn't its determinism/randomness depend on QM's determinism/randomness?

[/ QUOTE ]

This is a fascinating subject and your questions go to the heart of the fundamental nature of the universe. i suggest you look for a book on basic quantum theory. not university texts but one of the many aimed at the non-science "layman".

They will give you a feel of exactly what you are enquiring about and an introductory book would easily and quickly answer these questions you have posed.

For example, for some events the probability of an event happening is calculable by quantum theory (so you might say determinable by quantum mechanics) but the actual outcome of of a given measurement is not.

The apparant randomness is not an uncertainty due to limits of our scientific knowledge to predict an event. We "know" (in that QM has been extensively tested and not found wanting)that the uncertainty is a fundamental character of the universe at small scales.

Quntum theory absolutely does not say you can never know the position of a particle, just to pick up on another point .

Anyway, I really would urge you to continue your investigations into this and other areas of science, if you haven't already!