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What causes the expansion of the Universe and spacetime itself? One of the biggest successes of the 20th century was the development of Quantum Field Theory (QFT) which combines ideas of a wavefunction to describe particles from Quantum Mechanics with the laws of Special Relativity to predict the outcomes of high energy scattering experiments, like those in particle accelerators! QFT provides a mechanism for negative pressure (necessary for spacetime expansion) in the form of Virtual Particles. These are particle-antiparticle pairs which form due to fluctuations in quantum fields driven by the Heisenberg Uncertainty Principle. This allows particles to constantly come in and out of existence in incredibly small time intervals all over the Universe - including in vacuums.
However, when the theoretical prediction of the strength of this negative pressure or intrinsic vacuum energy is calculated in QFT, a value that is many orders of magnitude larger than the measured value from astrophysics and cosmology is found. This has become known as the worst prediction in all of physics, highlighting a major flaw in quantum theories on universal scales. While cosmology is useful for describing the bulk properties of vacuum energy (also sometimes referred to as Dark Energy), it gives almost no insight into what causes it on small scales.
This video also discusses Virtual Particles more critically by evaluating attempts to prove their existence (such as the Casimir Effect) and other consequences of them in our Universe (such as Hawking Radiation and the evaporation of Black Holes).
This video was sponsored by Brilliant.
0:00 - Energy In True Vacuums in Physics?
0:30 - Quantum Fields and Vacuum Fluctuations in QFT
2:00 - Heisenberg Uncertainty Principle in Energy and Time
3:11 - Energy of Empty Space and Spacetime Expansion in Cosmology
4:08 - The Worst Prediction in all of Physics
5:04 - The 'Existence' of Virtual Particles
6:20 - Evidence - The Casimir Effect and Wave-Particle Duality
8:00 - Alternate Explanation - Van der Waals Forces
8:51 - Relation to Hawking Radiation and Black Hole Evaporation in Astrophysics
