What Does it Mean that Radioactive Decay is a Random Process?
Does radioactive decay challenge the Kalam cosmological argument?
The Kalam cosmological argument starts with the premise that “everything that begins to exist has a cause.” Many atheists have questioned this assumption.
The premise is a little too strong in my view. It’s not possible to prove empirically — few things are. We cannot rule out the possibility of uncaused events in the universe. As our atheist friends remind us, it’s not easy to prove a negative.
But it’s another thing altogether to assume the universe does not have a cause (metaphysical naturalism). Or to act as if metaphysical naturalism is true — until sufficient empirical evidence contradicts that view.
If we are going to assign the burden of proof to those who question metaphysical naturalism, we first need to establish if an uncaused universe is even possible. If this assumption is to reflect reality, we ought to observe a plethora of uncaused effects in our uncaused universe. This article looks at a common example cited by atheists — radioactive decay.
What is random?
Let’s start with a version of the argument:
There is no known way to predict the timing of the radioactive decay of single atom e.g. from isotope Carbon-14 to Carbon-12.
“Radioactive decay is determined by quantum mechanics — which is inherently probabilistic. So it’s impossible to work out when any particular atom will decay, but we can make predictions based on the statistical behaviour of large numbers of atoms.”
This is correct, but why would this suggest radioactive decay is uncaused? The inference is that because radioactive decay is a random process it is, therefore, uncaused or has no known cause.
At first glance, that has an intuitive appeal. If we bump into a friend unplanned, we say: “We met them randomly”. There isn’t a cause for our meeting — it happened by chance. This is an example of our everyday use of random. But is that what we mean when using the term random in mathematics, physics, or other sciences?
An example
Before we jump into radioactive decay, let’s start with a more everyday example of what we mean by random in maths. Are double-jabbed people at less risk of dying from Covid-19?
A recent Centers for Disease Control and Prevention(CDC) report found 91% of those who died of Covid-19 in the US were not fully vaccinated. A much smaller number of deaths were observed in those who had been fully vaccinated (9%).
In CDC’s epidemiological study, death by Covid-19 was a random variable. Most people who were fully vaccinated did not die through Covid-19 — but some did. We cannot predict who will die of Covid-19, or when, only that the vast majority of fully vaccinated people will not.
A random variable is an outcome that can be estimated by a probability distribution. This means, that there is a certain probability attached to each possible value. In our example, there are two possible scenarios:
- death from Covid-19 or
- remaining alive /dying of a different cause.
Radioactive decay
If you’ve managed to stay with me, we can now get to the question. Radioactive decay happens in unstable atoms called radionuclides. A nucleus can decay by radiating alpha particles, beta particles, or gamma rays.
Radioactive decay is a random process. Here’s some revision of secondary school physics:
It is not possible to say which particular nucleus will decay next, but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. Scientists cannot tell when a particular nucleus will decay, but they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed.
This rate of radioactive decay is measured in half-life: the time it takes for half of the radioactive atoms to decay. It is this principle that forms the rationale for radiocarbon dating. All living things absorb carbon, including radioactive carbon-14:
When the plant or animal dies, they stop absorbing, but the radioactive carbon that they’ve accumulated continues to decay. Measuring the amount left over gives an estimate as to how long something has been dead.
Mathematical or everyday randomness?
When we speak of radioactive decay as random, what do we mean? We do not know which particular nucleus will decay — or when it will decay. But we can measure and predict the decay rate.
Similarly, we do not know which fully vaccinated people will die from Covid-19 — or when they will die. But we can estimate their death rate compared with those who are not fully vaccinated.
Since death from Covid-19 is mathematically a random variable, does that mean the lower risk in the fully vaccinated population is uncaused? Not at all! The CDC study, and many like it, provide strong evidence of a causal association between vaccine status and death from Covid-19.
Nor do we conclude that radioactive decay is uncaused. We know that the cause of radioactive decay is too few, or too many, neutrons in a nucleus.
Kalam revisited
The first premise of the Kalam Cosmological argument — “everything that begins to exist has a cause” — is difficult to test empirically. But we can assess the validity of this assumption based on current data.
We have lots of evidence from our everyday experience for the causality principle. If someone punches me in the face — it hurts. There is also a dose-response relationship. The more force someone hits me with the more it hurts!
The scientific method depends on the assumption that the causality principle is valid. As we saw with the Covid-19 vaccines — the most trusted ones were those with clinical trial results.
People were randomized to either receive a vaccine or a placebo — to ensure that the groups were similar on everything but receiving the vaccine. Those who received the vaccine were less likely to develop Covid-19, be hospitalised, or die. Scientists, therefore, concluded these improvements in health outcomes were caused by receiving the vaccination.
So if causality is a central aspect of our experience and the scientific method, wouldn’t it be a reasonable starting assumption that: “all things that begin to exist have a cause”?
Of course, this is a provisional assumption. Our scientific knowledge has its limits. In the future, evidence may emerge that leads us to challenge this judgment.
What is the default?
Some atheists assume the causality principle does not apply to the origin of the universe (metaphysical naturalism). Or frequently they assume methodological naturalism:
“a conscious decision to act… as if metaphysical naturalism is true”(Prof Michael Ruse, Oxford Handbook of Atheism, p383).
If we are to act as if the universe was uncaused, should we not first examine if this is even possible or probable? Arguments from radioactive decay attempt to do that but fail because of confusion between everyday and mathematical definitions of random.
There is insufficient evidence to conclude it is even possible for the universe to be uncaused, therefore we should exercise more scepticism towards methodological and metaphysical naturalism.
