 This is Thambon Becky, South Africa's president between 1999 and 2008. He became famous for his denial of the link between the human immunodeficiency virus, HIV, and the immunodeficiency disease, AIDS. Despite overwhelming scientific consensus that HIV causes AIDS, he suggested instead that the causes of AIDS were related to overall low levels of health care and poverty in the country. He denied treatment to AIDS patients and suggested alternative cure such as garlic, beetroot, and lemon juice. His policies are now estimated to have led to more than 300,000 preventable deaths. Thambon Becky belongs to the growing number of people trying to deny, vilify, and reject scientific claims in a movement generally referred to as science denialism. Science denialism is not a new phenomenon. Think of Galileo Galilei, an Italian scientist from the 17th century that is considered to be one of the fathers of modern science. In Galileo's time, people believed the earth to be at the center of the universe. Galileo tried to demonstrate with his astronomical observations that the earth and all of the other planets move around the sun. This led into a conflict with the Catholic Church that forced Galileo to deny his ideas in a now very famous trial. Unfortunately, similar claims such as that the earth is flat are well persisting into the 21st century. Flat earthers may not pose such a big risk to society, but unfortunately this is not always the case. For instance, establish and secure cures such as vaccines are now being put in doubt in a movement referred to as vaccine hesitancy. Vaccinations help prevent between two and three millions childhood death every year, but the growing number of non-vaccinated children is rising more than one concern. The World Health Organization declared vaccine hesitancy as one of the biggest threats for global health in 2019. And this is even more the case when we talk about measles. Measles was an illness that was once thought to be eradicated and is now surging back all over the world. In this chart you can see the number of measles cases in the United States in the decade going between 2010 and 2019. It is clear that there was a huge explosion in cases in the United States that led in 2019 to an increase of almost 20 times the number of cases compared to 2010. We are witnesses of a constant degradation of the scientific endeavor. In order to fight this trend it is necessary to understand what science is and why we should believe in science. In order to do so today I would like to show you what a scientific theory is, how scientists get to a scientific theory and how it is possible to distinguish between scientific and non-scientific theories. But before doing so it is important to understand what scientists mean when they talk about a theory, which is slightly different than how the world is used in our everyday life. Commonly we talk about a theory as an idea or a guess that we have about something that has happened and that might not be really connected to reality in any way. In science we refer to the world theory as a description or a story that allows us to interpret observations and facts. We can then play with this story in order to uncover relationships in the real world. But how do scientists get to a scientific theory? Let us imagine to have two magnets in our hands. Once we put them close together we might observe two different phenomena. The magnets might repel each other or the magnets might attract each other. Imagine how to do so with more and more magnets and always to observe the same effect. We might wonder why do we observe such effect? Is it possible to extract a general rule that allows us to predict the outcome of such experiment? What we just did was to start from a real empirical world observation and try to extract a general rule. This approach has been used in science and in scientific discoveries for ages and is known under the name of scientific method. As just said, the scientific method starts from an empirical observation that leads to an hypothesis. In our case the hypothesis might be that there is a force driving the two magnets close together or further apart. And that this force depends on the orientation of the two magnets. Once we have a hypothesis we must be able to perform and design new experiments that might prove or falsify our hypothesis. Once we get the results of these experiments they might go in two different directions. They might deny our hypothesis and in this case we might need to reformulate and go through the loop once again. Or our experiments might confirm our hypothesis. And thus we would be able to elevate our hypothesis to the role of a scientific theory and accept it as a valid description of the phenomenon we are studying. In our case the fact we observe with magnets are due to magnetic fields and now we know that each magnet has two different poles, a north and a south pole. Same poles repel each other and opposite poles attract each other. But what makes the magnetic field theory scientific? The crucial feature of every scientific theory is that we must be able to test in the real world what the theory predict is going to happen. This means that we must be able to have real observation and real experiments that prove and show what our theory wants to tell us. This feature is called testability and it allows us to distinguish between theories that are scientific and theories that are non-scientific or pseudo-scientific. Today I will focus on three different characteristics of a testable theory. Falsifiability, repeatability and reproducibility. Let me start with the principle of falsifiability. Once again please bear with me because we are meeting a world that has a slightly different meaning in science than it is in our everyday life. The principle of falsifiability states that a scientific statement is one that could possibly be proven wrong. This means that we must be able to think of a real experiment that might show that our theory is false. The keyword here is possibly. Possibly means that the principle falsifiability doesn't state that our theory is necessary false, but only that we must be able to think of ways to prove it false. In order to make this principle easier to understand, let me give an example. Let's pretend to have a theory and let's call it theory number one. Theory number one states that there is a planet between Mercury and Earth. This theory is falsifiable. Indeed we can think of experiments that might prove whether there is actually a planet between Mercury and Earth. For example, we might think of having a telescope that looks what is before Mercury. Of course what we know nowadays is that there is actually a planet there and it's called Venus. This makes the theory real in practice but also falsifiable since we were able to think of an experiment that might have possibly proven our theory wrong. Having a theory that is falsifiable makes it easier for us to justify and believe in such a theory. Let's now go to the other end. Let's take theory number two. Theory number two states that there is a China teapot orbiting around the sun. Between Earth and Mars. Theory number two also states that this China teapot is undetectable by any telescope or technology known to human. This is of course a problem and this makes theory number two unfalsifiable, not falsifiable. Of course we cannot detect the teapot if we have no instrument to actually see if the teapot is there. This makes it difficult to justify and believe in theory number two. As you saw with theory number one, scientific theories are all about taking risks. We have to think of ways that might prove our theory wrong and then test if the theory is actually wrong. Moreover, scientific theory makes both predictions. We try to falsify our theory and until we cannot do that we think of the theory to be true and we believe in our theory. There are theories that do not take any risk. They are not falsifiable. In science this is considered to be a weakness and not a strength of the theory. Finally, let me highlight once again that falsifiability doesn't necessarily mean that our statement is wrong. Falsifiability allows us to keep in mind that there could be a new observation coming in the future that proved our theory to be wrong and false. If this happens we would be able then to change or modify our theory and this is our science advances. We said that for our theory to be testable once we have a scientific statement we need to be able to think of experiments and the results that might falsify our theory. In order to get really scientifically valid statements these results must be repeatable and reproducible. The principle of repeatability means that we must be able to perform the same experiment over and over starting from the same observation going through the same experimental setting and using the same instrument. If this is possible and we always obtain comparable results we have a repeatable experiment. Repeatability ensures that you as a scientist can trust your own results. Let me once again go back to the example of our magnet. A scientist would be interested to take two magnets and keep on putting them close together in order to observe whether they attract or repulse each other based on their orientation. If this happens the theory and the results are repeatable. Once we have a scientific statement that is falsifiable in our opinion and for which we have identified experiments that might prove it false we expect these experiments to be universal or reproducible. This means that if we have different teams of scientists scattered all around the world they must be able to start from the same question use their own observations and their own instruments but get to comparable results. Once again if we want to see whether the magnetic field theory allows us to have reproducible results we would have scientists scattered all over taking their own magnets putting them close together and observing whether they attract or repulse each other based on their orientation. If this happens the results are reproducible. We now have all of the instruments that might allow us to evaluate whether a theory is scientific or pseudoscientific. Allow me to give you one last example of a very famous scientific misconduct case that led to devastating consequences and that started one of the main trend in the vaccine hesitancy community that vaccines may cause autism. In 1998 British doctors Andrew Wakefield stated that vaccines that were supposed to cure measles, mumps and rubella the so called MMR vaccines were supposed to cause autism. Of course this piece of news and of research quickly spread all over the world and led to almost immediate drop in vaccination rates. But there was a fundamental problem. Group of scientists immediately tried to reproduce and find whether there was actually a link between vaccines and autism and they were not able to. Wakefield's results were not reproducible. Therefore from a scientific point of view his statement was not valid and could not be considered more of a normal personal opinion. Eventually what was discovered during an investigation was that Wakefield was working after being paid from private law firms that wanted to force a link between vaccines and autism in order to open lawsuits against vaccine manufacturers. Here I come to an end. Today I showed you what a scientific theory is and how common language and scientific language may differ. I showed you how scientists get to a scientific theory using the scientific method. Finally I hope I demonstrate that there are a few instruments that might allow us to evaluate whether a theory is scientific or not scientific and this would be whether a theory is falsifiable, repeatable and reproducible. Thank you very much. Thank you. Any questions? Raise your hands. There is one over there in the front row. As you're also a neuroscientist, do you find some strong correlation between the people who tend to go for anti-vaccinations, conspiracy theories, anti-migrants as well and they tend to be on the right side of the spectrum if you know what I mean of the politics? Do you find a strong correlation in all of that? Importantly, what's the main reasons behind it? Is it how their brains are wired? Also religion comes into place as well but let's move it out. To be honest I think it's quite risky to affirm something in that direction and I honestly wouldn't feel like doing it also because I have no numbers in my hand that confirm in any direction what you have just suggested. For sure there are different reasons for people tending not to believe in science and scientific theories or in vaccines in particular. And this might be related to education, that might be related to religion, prior beliefs, the society they are born in which of course plays a big role but I think it's very difficult to find a common denominator in all of these kind of trends and behaviors. Yeah I have no numbers you know so I mean again as a scientist if I have no numbers and especially then deriving casual relationships is always kind of tricky so I wouldn't they're saying something especially now in some situations. I think that was a great example of sticking to the scientific method. Any other questions? Don't be ashamed. There is one over there. There is a little bit of an idea that science is also a social process and basically boiling it down to the very strict philosophical principles is maybe not doing the real scientific process as it happens at a university and in the journals of justice. How much do you think do you see this in your own life and in your work or in the reality of science so to say? So I agree that often these two aspects are considered to be quite different and to a certain extent they must be considered to be different. But I do believe that in order to have meaningful scientific results that can have a real impact it is necessary to have this principle in mind and unfortunately I'm not sure how many people actually either in science or outside of science really know this principle and that's why I deeply believe it is necessary for everyone to have a basic knowledge whether you're in science or not doesn't really matter to have an understanding of what it actually means to do science or do experiments. Thank you for this answer. I would advise you to find him after the event for your other questions. Ask our time for questions on the stage is up. So thank you very much. I would give him a warm applause.