B Is Radioactive Decay Uncaused/Causeless?

8
0
I know that it has a cause! It happens to make the nucleus more stable. But some say it has no cause. I am confused actually.
 
Well, the reason that certain nuclei decay in general could could be seen as the fact that other configurations are energetically favorable, yes.

But for a single nucleus, the decay is inherently random, e.g. it will decay at some random time, without any further cause. You can predict how many nuclei in an ensemble will decay on average over some period, but not if a particular nucleus will decay during that time, or when that nucleus will decay, or even at what specific time any nucleus in the ensemble decays.

Or to put it different: If you have two nuclei, and one decays after some time, there is no reason or cause why this one and not the other decayed, that question does not even make sense really.
 
8
0
Thanks, I know that there are three types of decay (alpha,beta,gamma). Does weak force work on all these types of decays ( I heard only the beta decay is affected by weak force)
 
33,384
9,107
Only beta decay. Alpha decay is mainly due to the strong interaction (the electromagnetic interaction is still relevant, however), gamma decay happens via the electromagnetic interaction.
 
8
0
then is it that Only Beta Decay is uncaused ?
 
8
0
thank you very much, then the whole point is that it doesn't explain why it sometimes decays and sometimes remains undecayed, hence it is uncaused.
 
Last edited by a moderator:

Orodruin

Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
2018 Award
15,945
5,917
thnk u very much, then the whole point is that it doesn't explain why it sometimes decays and sometimes remains undecayed, hence it is uncaused.
This is not correct. The cause is the type of interaction responsible for the decay. However, those interactions work in a probabilistic manner due to quantum mechanics and therefore have a certain probability per unit time of causing a decay.
 

russ_watters

Mentor
18,849
5,039
thnk u very much, then the whole point is that it doesn't explain why it sometimes decays and sometimes remains undecayed, hence it is uncaused.
The fact that single events in a probabilistic distribution are random/unpredictable does not at all mean uncaused. There's no easy way to predict what number comes up when rolling dice, but that doesn't mean there's no cause or clearly known probability for that matter.

This is a misunderstanding of what "random" means/how it applies.
 

anorlunda

Mentor
Insights Author
Gold Member
7,553
4,263
I think "cause" is not the best word for your question.

If we have N nuclei, all identical. In a period of time, some may decay, other's don't. That is a "random" process.

The physics phrase that better fits your question is "hidden variables". Is there some variable or property of the N nuclei that we don't know about that "causes" certain ones decay? The answer is, "No." Many scientists, including Einstein, dislike that answer. But it has been verified by experiments.
 
22
9
I know that it has a cause! It happens to make the nucleus more stable. But some say it has no cause. I am confused actually.
Few days ago, I read an article "Half-life" in the page askamathematician.com. An extremely simple explanation of the phenomena

Please tell me if I am proceeding in a wrong way giving the link ....

Daniel
 

ohwilleke

Gold Member
1,470
375
thank you very much, then the whole point is that it doesn't explain why it sometimes decays and sometimes remains undecayed, hence it is uncaused.
All Standard Model physics is fundamentally stochastic rather than deterministic. "Uncaused" is an unhelpful word to use in this context that clouds understanding rather than enlightening.

Even outside physics, the term "caused" isn't restricted to deterministic processes. If you change a system (e.g. by removing a guard rail) to make something that was previously very unlikely (falling off a cliff), much more likely, and the thing that is more likely (i.e. someone falling off the cliff) ends up happening, you are considered in plain English and in moral philosophy and in law, to have caused that event, even though you only changed its probability and did not make it happen in a deterministic sense (e.g. by pushing someone off the cliff). The fact that something has a probabilistic component doesn't mean that it is "uncaused". The existence of an atom of a particular type for a particular duration is a cause without which the decay wouldn't have happened.

Alpha decay, beta decay and gamma decay all occur because the particular configurations of fundamental particles interact with certain probabilities (which are quantified by the coupling constants of the fundamental forces), and thus happen in predictable ways that are random within the confines of those probabilities.

The reason that one atom like lead is stable, and another atom like plutonium is unstable, is somewhat analogous to the way that the odds of the dealer in a game of blackjack getting at 21 hand is a function of how many facecards in the deck have already been played and hence the composition of the deck that is still being dealt. The complex makeup of the system that is producing decays influences the probability that new events of a particular type will happen in the future.

The decays are caused by the circumstances that create a probability of them happening or not. But, the fact that we know the cause and the precise probability of them happening, does not mean that we know precisely when a particular atom is going to have a particular decay.

In other words, fundamentally in metaphorical terms, to contradict Einstein's famous aphorism, as we understand the laws of physics today, God not only plays dice with the universe, God is, in fact, the greatest gambling addict that there ever was and ever will be. The dice are being continually rolled and we only see the results that are observable and not the rolls of "nothing happens."

The word observable with the naked eye and in our common experience only seems deterministic, because the law of averages and the extremely large number of events involved, mean that most macroscopic phenomena have such low statistical uncertainty that they are almost deterministic.
 
Last edited:

ohwilleke

Gold Member
1,470
375
I think "cause" is not the best word for your question.

If we have N nuclei, all identical. In a period of time, some may decay, other's don't. That is a "random" process.

The physics phrase that better fits your question is "hidden variables". Is there some variable or property of the N nuclei that we don't know about that "causes" certain ones decay? The answer is, "No." Many scientists, including Einstein, dislike that answer. But it has been verified by experiments.
If phenomena that appear random are indeed actually deterministic, then (1) the system while deterministic is at least "chaotic" in the mathematical sense that the outcome is hypersensitive to inputs that are slightly different from each other, and (2) the inputs are completely decoupled from the observable world to such an extent that they product completely unbiased outcomes given what we can control for from what we can observe, which is as a practical matter, indistinguishable from random.
 
47
43
An airline servicing roadless interior Alaskan villages with 32 flights per day needs accurate weights. For twelve months (1980) every person on every flight was run across a scale. By the end there was every confidence that passengers weighed exactly 163 pounds. Planes could be loaded and fueled knowing they were in limits. 16 passengers weighed 2608 pounds often enough to bet money on it.
Now when Ted showed up he got a special seat under the wing as he checked in at 455 pounds. Susan and her group barely reached 300 for the five of them.
Small scale with limited sample size but it still produced workable numbers.

What caused any of them to fly any particular day? Nothing predictable on an individual basis.
 

DEvens

Education Advisor
Gold Member
1,007
302
The idea of "uncaused" is kind of off the mark. This is not specific to radioactive decay, it's quantum mechanics.

So let's play a quantum mechanics game. Suppose I have a pair of ordinary six-sided dice.

dice.jpg


Suppose I tell you that I will have chicken for lunch on an odd roll, and pizza on an even roll. It comes up 7 so I have chicken.

Is this uncaused? It would seem not, since the reason I had chicken was because I got a 7.

Suppose that we assume that, given enough care and accuracy, I could have predicted before the roll that 7 would come up? Does it change whether my chicken-choice was uncaused? It would seem not. The choice would seem to have been made by whatever factors produced that 7.

Suppose we assume that, no matter how careful and accurate we were, it is impossible to predict the outcome of the dice in advance. But suppose that the reason is that they are put through a process that causes small uncertainties to grow. For example, if the first bounce is off by 1/100th of a degree, the next one might be off by 1/10th, the next bounce by 1 degree, and quickly they go away from the prediction. This is the reference to chaos upthread. So any finite degree of uncertainty, which a measurement will always have, will grow rapidly. And the results are rapidly unpredictable. Weather forecasts more than 5 days out are quite unreliable.

Now let's suppose a different thing. Let's suppose that there is uncertainty inherent in the material of the dice. Let's assume quantum uncertainty such that, in principle, it is not possible to predict the outcome. No matter how accurately we prepare the dice the results can come out different. The canonical example is a transistor driven in such a way that thermal noise produces a random signal. This can be used to produce a series of binary bits, which can be converted to numbers. I could roll my dice using such a system.

Suppose I assume that such a system can't be predicted in principle. Not because it's chaotic, but because observing the system causes it to randomly select a particular eigenstate, so it produces a particular measurement value. The probabilities of each possible reading can be set up to be repeatable. But the next measurement is not predictable. This would be a particular meaning of causality and deterministic. The influences that set up the probability are all in the past of the system, in the backward light cone to use the buzz phrase. But it's not deterministic. There is no way to predict the next result, not even in principle.


This is the point of Bell's theorem. It tells us that a deterministic system would behave differently from a quantum random system, that we could distinguish the two.


The result is, quantum mechanics keeps causality but drops determinism. The things that set the probabilities are all in the past light cone of the system. But the results are not the same every time. They are random.

So here's the thing. Suppose somebody wants to reject this notion of non-deterministic causality. It can't be that way, they might claim. The thing they need to do is demonstrate that quantum mechanics does not agree with observations. So far, it does. And quite remarkably well. Just as an example of that, consider the anomalous magnetic dipole of the electron, which is now something like 9 digits of agreement between theory and experiment.

 
33,384
9,107
The result is, quantum mechanics keeps causality but drops determinism.
This is not the right place to go into details but I would like to point out that this statement only applies to some interpretations of quantum mechanics but not all of them.
consider the anomalous magnetic dipole of the electron, which is now something like 9 digits of agreement between theory and experiment.
12 digits if you take the whole dipole moment (2.002...)
 

ohwilleke

Gold Member
1,470
375
An airline servicing roadless interior Alaskan villages with 32 flights per day needs accurate weights. For twelve months (1980) every person on every flight was run across a scale. By the end there was every confidence that passengers weighed exactly 163 pounds. Planes could be loaded and fueled knowing they were in limits. 16 passengers weighed 2608 pounds often enough to bet money on it.
Now when Ted showed up he got a special seat under the wing as he checked in at 455 pounds. Susan and her group barely reached 300 for the five of them.
Small scale with limited sample size but it still produced workable numbers.

What caused any of them to fly any particular day? Nothing predictable on an individual basis.
I'm sure you have a point, but I'm too dull, I guess to see how this example connects with the question. I would need a few more dots connected and analogies spelled out to get it.
 

Want to reply to this thread?

"Is Radioactive Decay Uncaused/Causeless?" You must log in or register to reply here.

Related Threads for: Is Radioactive Decay Uncaused/Causeless?

Replies
7
Views
261
Replies
7
Views
3K
  • Posted
Replies
4
Views
3K
Replies
7
Views
543
Replies
2
Views
19K
  • Posted
Replies
2
Views
2K
Replies
2
Views
648
Replies
2
Views
3K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top