The speaker discusses the biggest open problem in fundamental physics, which is the lack of understanding of a vacuum, also referred to as "nothing" or "emptiness". They explain that the vacuum is not a literal "nothing" but a kind of permanent substance intrinsic to space itself. The speaker then delves into the concept of energy in a vacuum, explaining that it's not zero and that it can be measured by observing the universe's expansion.
The speaker then discusses a problem known as the cosmological constant, which states that the energy of the vacuum is the sum of two terms: one due to gravity and the other due to the "sea" that gives rise to elementary particles. The speaker mentions that the known energy of the vacuum is much greater than what is predicted by the theories, leading to a discrepancy of 10^60 protons per cubic meter.
The speaker then discusses the implications of this discrepancy, suggesting that it could mean that the three terms contributing to the vacuum energy - the cosmological constant, the energy of the "sea" associated with known particles, and the energy of the "sea" associated with unknown particles - are not independent, which would be a departure from the principle of independence in nature.
The speaker concludes by suggesting that this problem could be the door to the next great revolution in physics and that the answer to many of the most important questions in physics boils down to one: we don't know what nothing is.
1. The speaker identifies the biggest problem in fundamental physics as the lack of understanding of a vacuum, describing it as the "mother of all mysteries" and the "greatest mystery of contemporary physics" [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
2. The speaker explains that what physicists refer to as "emptiness" or "nothing" is actually a "permanent substance" intrinsic to space itself, which cannot be eliminated [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
3. The speaker further explains that the energy of the vacuum, which we perceive as gravity, is not zero and has a significant impact on the expansion rate of the universe [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
4. The speaker reveals that the energy of the vacuum in a cubic meter of space is equivalent to the energy contained within a proton, a very small amount [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
5. The speaker discusses the problem of the cosmological constant, stating that the energy of the vacuum we measure is significantly greater than the energy of the vacuum we calculate from our physical theories [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
6. The speaker suggests that the three terms that contribute to vacuum energy, which refer to very different physical phenomena, could be secretly connected, challenging the principle of independence in nature [Document 1](https://www.youtube.com/watch?v=00:00:00.64).
7. The speaker concludes by stating that the biggest problem with fundamental physics is that we don't understand what "nothing" is [Document 1](https://www.youtube.com/watch?v=00:00:00.64).