Could this happen?, I saw something wierd in physics-class

Hi. I saw something really wierd in physics-class.

We measured the radiation of Caesium-atoms, and found out that sometimes there came more radiation than other times, and it was all unpredictable. How can this happen? Everything else we've measured in physics class obeyed logic and fundamental laws of physics and that every event is because of something else. But this radiation from the Caesium atoms seems like it is just totally random...

How can this happen? Is there any kinds of hidden variables that we don't know of? Is there other radiation in the room that could have caused it? I cannot accept that something can be random, because it can't. It is against the laws of physics.

Id have to say that quantum mechanics would tell you differently. All things are completely random but do not appear so when we average out all the randomness. Essentially, everything is statistics and has a probability of occuring at a quantum level. It just so happens that with the immense number of things happening at this level, they average out to what we observe in the macroscopic world.

So, if you are into philosophy we kina screwed up the idea of causation in a pure sense

look at it this way. Radiation is caused by the decay of the Cesium atom into a lighter atom. I'm not sure what kind of radiation it is or what kind of decay it is, or what it decays into, I'm sure someone here can give you the details. but that will give us a basis to start from.

Each atom in the sample must decay at some point. but we really don't know when any given atom is going to decay. some will go quicker than others. which is why we measure decay in half lifes. we can say statiscally speaking, after so much time, half of the atoms will have decayed. but we don't know which half.

So what you are measuring, is the paricles given off by individual atoms as they decay. over all, you will have a pretty constant rate. but sometimes more atoms will go off at the same time, and sometimes less will go off. so you will have variations.


From a computer programming point of view. if you have a grid of 1000 cells that are all black, and you set up an algorythm to pick a random number between 1 and 1000 and then cause that cell to change color, after running the program for a long time, some of the cells will still be white. and many will have changed colors many times. and you really can't predict which ones will change and which ones won't.

Is it really correct that something "can't" happen because "it's against the laws of physics"? What if the thing does, in fact, happen? Surely the laws of pyschics aren't fixed. And even if they were, we'd still be concluding that the laws are of physics are being followed simply because that's the best conculsion we can make given the information we have. I don't think we could "prove" once and for all that the conclusion is a perfect matchup with the state of things. The conclusion would be the best assessment of the state of things that we can manage. -- Slacky B

Your choice of words here is interesting because they're exactly what Einstein used in his search for the reasons behind why an individual atom suddenly fissioned. He couldn't accept that it was totally random and assumed there was some cause for the fission hidden inside each atom. He never found the cause and it's now accepted that there is no "cause".

Probably the nearest answer as to why an atom suddenly fissions after sitting around for millions or billions of years comes from the idea that all atoms tend to "wobble" like jelly or a drop of water in zero gravity. Of course, an atom's wobble never stops like a drop of water would. This wobble means it's continually changing shape and the larger the atom the more it wobbles. The wobble is also affected by how the atom is "glued" together by the number of neutrons. If the wobble is a chaotic system then a slight extra wobble can suddenly build up to a point where it can't hold itself together any longer and it splits apart. Wait long enough and sooner or later this chaotic wobble will occur in every atom large enough (or weakly glued) to break it apart. Because it's chaotic it could happen in the first second after the atom was formed or it might take a million billion years. But with a collection of trillions of atoms some of them will be fissioning at the very moment you're looking at them.

well first, the scientific community would all claim that it didn't happen and that it was some kind of a hoax. propbably perpertrated by the religious right.

some people might disappear, and the person who claimed to witness this happening would have his credibility assulted in a major way.

If somehow they survive this, and other people are able to make the same thing happen in controled conditions. then after a great deal of time and many many more research, we would simply change the laws of physics, which were in error before. and the person who discovered it would win the nobel prize, or more likly, the one who figured out why it happened and fixed the theory.

this is why we call them theories, and not facts, there's always a chance that someone will come up and point out a flaw or some observation that wasn't accounted for by the theory.

I probably shouldn't be quoted on this, because it's been a few years since I had that course in college. But, I believe that some atoms have different probability of releasing different amounts of energy or particles when they decay. Such as alpha particles, beta particles, etc. I don't know if Cesium is one of these though. It seems to me that if it were, your teacher should have known enough to tell you so. So maybe my answer doesn't fit. Anyone more knowledgeable out there care to take this on?

Quantum physics says for every radioactive atom of a certain type (initial state) it has the same probability in a given time of decaying (transition rate to final state is constant). If you have a great many atoms, or average over a period of time, then the number of undecayed atoms will be modelled by the differential equation dN/dt = -K N which leads to the solutions N = N_0 exp(-K t). And the radioactivity will be KN = K N_0 exp(-K t).

It's important to remember that these atoms are not hooked up to some sort of schedule. Their decays are random and uncorrelated.

In classroom exercises, you probably will not have a large amount of radioactive material. In all likelyhood you will have a small amout of a modestly radioactive substance (both K and N_0 will be small, and since K is small we can approximate N = N_0). Your detector will not measure all of the radioactivity (which comes in a random direction), but only the radioactivity that hits it. So the expected count of radioactivity measured in a unit of time is proprotionate to K N_0.

But if this number is less than 1000, large percentage changes are statistically expected. Every atom has a random and uncorrelated expectation of when it will decay, and the direction will also be random an uncorrelated, so statistical sampling laws apply. (This is the same reason newspaper polls say they have an error margin of +/- 5% or 3% -- because if we take a random sample that is small, we have a chance of picking an uncharacteristic sample.)

wikipedia: Radioactivity

Simulated Radioactivity Lab Exercise

What happens durring half lifes when there is only one atom left?

Hi,

I have read that it may be possible to change the radioactive decay rate of any set of particles by applying the proper dynamic E/M fields. Also, I think that gravity and the state of the local reference frame do have effects on this rate.

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