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Why is the future different from the past? The most poignant property about the world around us is that time is always moving forward, yet, as odd as it may seem, our current theories of physics cannot account for this property. In all of fundamental physics, the future and the past are entirely similar. We select time increasing solutions by hand and call on extremely unlikely initial conditions at the big bang to justify this choice. I will address this question and describe attempts to restore the irreversibility of time as the building block of our understanding of nature.

This talk was delivered at ISSYP 2019, Perimeter's high school summer program.

Abstract: There is a strong correlation between the sun rising and the rooster crowing, but to say that the one causes the other is to say more. In particular, it says that making the rooster crow early will not precipitate an early dawn, whereas making the sun rise early (for instance, by moving the rooster eastward) can lead to some early crowing. Intervening upon the natural course of events in this manner is a good way of discovering causal relations. Sometimes, however, we can't intervene, or we'd prefer not to. For instance, in trying to determine whether smoking causes lung cancer, we'd prefer not to force any would-be nonsmokers to smoke. Fortunately, there are some clever tricks that allow us to extract information about what causes what entirely from features of the observed correlations. One of these tricks was discovered by the physicist John Bell in 1964. In a groundbreaking paper, he used it to demonstrate the seeming impossibility of providing a causal explanation of certain quantum correlations. This revealed a fundamental tension between quantum theory and Einstein's theory of relativity --the two central pillars of modern physics. It is a tension that is still with us today.