Montreal Gazette


But `high degree' of certainty is useful in many cases

- JOE SCHWARCZ The Right Chemistry Joe Schwarcz is director of Mcgill University's Office for Science & Society ( He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

Our word “science' derives from the Latin for “knowledge.” But knowledge is actually quite a complicate­d concept. Sometimes we can make a categorica­l, conclusive statement about having knowledge, but much more frequently, claims of knowledge have to be qualified with “ifs,” “buts” and “maybes,” terms that describe a degree of uncertaint­y. Indeed, certainty in science can be elusive.

When asked if I know what will happen if vinegar is added to baking soda, I can answer with total confidence that bubbles will form. But how do I really know that? Because I have done this many times, as have millions of others since 1846 when baking soda was first introduced, and bubbles have always formed. There has never been a single report of this not happening. And, of course, based on chemistry, I know that reacting acetic acid with sodium bicarbonat­e produces carbon dioxide gas. So, I am certain of my answer.

Now, what if I were asked if I know what will happen if a feather and a hammer are simultaneo­usly dropped from the same height on the moon? My answer would be that they hit the ground at the same time. How confident am I of this answer? Very. Like anyone who has studied physics, I learned how Galileo proved that Aristotle's theory about falling objects was wrong. The famous Greek philosophe­r had stated that if two objects of different mass were dropped from the same height, the heavier one would hit the ground first. It seemed logical, but Aristotle was not an experiment­alist.

Some 20 centuries later, Galileo Galilei was. Whether he actually performed the experiment of simultaneo­usly dropping cannon balls of different mass from the leaning tower of Pisa is debatable, but he did roll balls down a ramp at different angles and extrapolat­ed his observatio­ns to a sheer vertical drop, concluding that the time taken for a dropped object to hit the ground was independen­t of its mass.

Why, then, did a feather take a longer time to fall than a heavier object? Air resistance! This was proven in 1971 when astronaut David Scott, commander of Apollo 15, dropped a hammer and a feather on the moon from the same height and, as we clearly saw on television, they both hit the surface at the same time. Putting aside the ludicrous conspiracy theory that the moon landing and the video were faked, we can say that we know, without a doubt, that Galileo was right. There is no need to ask that this experiment be repeated by other astronauts to confirm the results.

Let's now turn to another question I have been asked recently and repeatedly. Does the presence of perfluoroa­lkyl substances (PFAS) in our drinking water pose a risk to health? I would have to say, maybe, but I don't really know. These chemicals, because of their oil-resistant and water-resistant properties, are found in numerous consumer items ranging from stain-free carpets and rain gear to cookware and cosmetics. Since they are manufactur­ed on an immense scale globally, it comes as no surprise that traces can be detected in our drinking water, especially given that today's sophistica­ted analytical techniques can detect substances down to concentrat­ions of parts per trillion.

Laboratory experiment­s with cell cultures and animals have shown that PFAS can have an effect on health, and that these chemicals can be detected in virtually everyone's blood. What we do not know is whether the amounts detected in blood are clinically significan­t or to what extent their presence comes from water. In order to have a conclusive answer, one would have to compare blood levels and disease patterns in a group of subjects who drank tap water with a control group who only drank water guaranteed to be free of these chemicals. Such a study, which would have to span several years, is logistical­ly and economical­ly not feasible, so we are left with the “maybe” conclusion.

Such uncertaint­y does not only apply to substances in our drinking water. There is uncertaint­y when it comes to the effects of COVID vaccines, the best diets for weight control, the effects of the microbiome on health, geneticall­y modified foods, vitamin supplement­s, sleeping aids, coffee, saturated fats, red wine consumptio­n, antioxidan­ts and a whole host of other factors that can affect our health and longevity.

However, even uncertaint­y is on a sliding scale and is subject to qualificat­ions.

For example, population studies have shown that people with cardiovasc­ular risk factors such as high cholestero­l, a family history of heart disease or are overweight are likely to benefit from taking statins. But whether a given individual will avoid a heart attack or stroke cannot be predicted with confidence. Similarly, while COVID vaccines reduce the risk of infection, not everyone who is vaccinated benefits.

Decisions come down to a risk-benefit evaluation, but even that is subject to change as more studies come to light. While limited alcohol consumptio­n used to be regarded as either innocuous or even beneficial, recent studies suggest that alcohol is a carcinogen and no amount of alcohol may be safe.

This uncertaint­y, which is inherent to many aspects of science, can drive one batty. One study finds that breakfast is the most important meal of the day, another argues that it is better to eliminate it. One study shows that artificial sweeteners are a great tool for weight loss, while another claims that not only are they useless, but unhealthy.

But let's not despair. Absolute certainty in science is indeed rare, but as studies accumulate and point in the same direction, we can arrive at a pretty high degree of certainty.

For example, I'm quite confident in saying that cutting back on sugar is a good idea, as is incorporat­ing berries and whole grains into the diet. Exercise is an important determinan­t of health, vaccines do not cause autism, smoking is bad, crystals have no healing power, spoons cannot be bent by the power of the mind, and homeopathi­c preparatio­ns are no more effective than placebos.

And I'll also go on record stating that I know, without any doubt, the Earth is not flat even though I have not had the experience of seeing its spherical shape from space.

Some things we know, some we are uncertain of. Science has some, but not all answers.

 ?? PATRICK BERNARD/AFP VIA GETTY IMAGES ?? Uncertaint­y, which is inherent to many aspects of science, can drive one batty, writes Joe Schwarcz. Citing difference­s in suggested safe levels of alcohol consumptio­n is one example of conflictin­g studies, he says.
PATRICK BERNARD/AFP VIA GETTY IMAGES Uncertaint­y, which is inherent to many aspects of science, can drive one batty, writes Joe Schwarcz. Citing difference­s in suggested safe levels of alcohol consumptio­n is one example of conflictin­g studies, he says.
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