This lecture, recorded before lecture 5, which was released a month ago, actually more naturally follows it, which is why releasing it after lecture 5, while unintended, actually makes sense. In the last lecture I described the most important unification in all of physics, the unification of electricity and magnetism, a unification into electromagnetism by James Clerk Maxwell in the 19th century.

Because of its elegance, and its overpowering utility, the theory of electromagnetism has provided the prototype for all modern physical theories that have followed it. As I show in this lecture, the form of electromagnetism is governed by a new mathematical symmetry in nature, called gauge symmetry. It turns out the existence of this symmetry is profoundly important, and it not only governs the exact form of the theory, it turns out to govern the form of all the known forces of nature.

Before we get to gauge symmetry, I want to explore more generally what is meant by symmetry in physics, and then I want to redo elementary physics by thinking about symmetry. In my mind, the fact that basic physics is introduced without reference to the symmetries of nature is perhaps the greatest failing in the teaching of modern physics. Concepts like energy and momentum have relevance because of fundamental symmetries of space and time. The facts that energy is ‘conserved’, and momentum is ‘conserved’ in systems, which rigorously fix determine the form of Newton’s laws of motion, are often introduced as if they are dictates on high, like the ten commandments. However, once one understands that these arise from symmetries of nature, the fact that these quantities exist and are conserved, becomes immediate, as the remarkable mathematician Emmy Noether showed at the beginning of the 20th century.

Finally, as important as mathematical symmetries are in governing physical laws, it is equally striking that even if these fundamental symmetries exist in nature, they may not be manifest in particular situations. For example, gravity and electromagnetism don’t distinguish between left and right, but if I look around my room, the left side of my room looks very different than the right side. This is an example of what is called ‘broken symmetry’, one of the most subtle and impactful notions at the basis of what is now called The Standard Model of Particle Physics.

In this lecture I review all of these ideas, which are essential if we are to go beyond the physics of the 19th century to understand the physics of the 20th and 21st centuries.

Enjoy.

As always, an ad-free video version of this podcast is also available to paid Critical Mass subscribers. Your subscriptions support the non-profit Origins Project Foundation, which produces the podcast. The audio version is available free on the Critical Mass site and on all podcast sites, and the video version will also be available on the Origins Project YouTube.

Happy August! . Heading back to North America as we just concluded our Origin Project Adventure to Cyrpus and Greece, where we felt the heat, and avoided some wildfires while having some amazing positive experiences as well with an amazing group of 26 travelers. Please stay safe and try and stay cool this month.

To help distract you from the heat, I hope you will enjoy this latest conversation about new discoveries in science with Sabine Hossenfelder. As always, we try and deconstruct the facts behind the headlines, and also explore new strange corners of our universe.

This episode begins with some new observations of the Bullet Cluster of galaxies. This cluster contains two galaxies that have collided, and seems to have provided evidence for exotic dark matter that has passed through the collision unscathed. Not so, says a new analysis, which claims evidence for more dark matter in the form of black holes and other less visible normal matter. There are strong reasons to be skeptical however, as both Sabine and I agree.

Speaking of black holes, a new analysis of collisions of black holes at the terrestrial gravitational wave detectors proposes a solution to the mystery of how black holes in a so-called forbidden gap between 10-20 solar masses and more than 50 solar masses have formed. They provide evidence that some of the black holes observed in collisions have been built up from earlier collisions with other black holes. This hierarchical growth could potentially explain how very large black holes in the early universe form, though it is a long way from 50 solar masses to 1 billion solar masses!

Strange goings on at the largest scales of the universe continue to be claimed, as yet another study argues for an unexpected and unexplained cosmic spatial asymmetry. It is hard to reconcile this with the observed uniformity of the universe on the largest scales we can observe via the Cosmic Microwave Background. As a result, it is too early to get excited, even if newspaper reporters love to report on claims that fly in the face of the standard model of cosmology.

The Vera Rubin Space Observatory has started its 10 year project to monitor a huge swath of sky every night looking for things that go bump in the night. On the first night, they found a few hundred thousand possible events. With a 10 year movie of the cosmos who knows what they will discover.

Sabine introduced me to an article about Quantum Batteries. Are they going to be useful, or just another cute example of how quantum mechanics produces strange phenomena? Time will tell.

Finally, I couldn’t resist introducing a story about cockroaches with nervous system implants that allow their motion to be remote controlled by experimenters, with tiny diving suits attached that allow them to breathe underwater for extended periods. It is claimed that they may help in undersea rescue.. Wow! Maybe so… What will they think of next?

Until the next time.. enjoy!

As always, an ad-free video version of this podcast is also available to paid Critical Mass subscribers. Your subscriptions support the non-profit Origins Project Foundation, which produces the podcast. The audio version is available free on the Critical Mass site and on all podcast sites, and the video version will also be available on the Origins Project YouTube.

I remember when my friend, journalist Claire Berlinski, first contacted me about a tragic situation regarding a family trapped in Afghanistan after the Taliban takeover. She knew that I had helped a young girl interested in physics escape to the US to study years earlier and hoped that I might assist in this case. If ever one imagined a family appropriate to bring to safety, this would be the one. The mother was a women’s rights lawyer before the takeover, and the husband worked for a French firm. The Taliban had broken into the Bar Association Office and found records of lawyers, who were being sought for arrest. One older son, and five young daughters in danger of being married off if they were discovered.

Their original escape plan was foiled when the airport was bombed just before their planned departure. Because Claire lives in Frances the older boy had reached out to her for help, and she sent out a call to her followers to provide financial assistance to help the family.

Claire contacted me because she knew I now lived in Canada, which has a well-established refugee program. In spite of this, for two years I was not able to find a single sponsoring agency who had a sufficiently large slot allocation to assist. Finally, after over a year, with five generous individuals who agreed to act as guarantors, Jewish Immigrant Aid Services in Toronto indicated they had the slots and would sponsor a refugee application for the family, provided we raised the necessary funds to guarantee support for family for their first year in Canada—a government requirement. After five months of fundraising, we achieved the goal, and the full application was submitted to the government of Canada.

I have always found it poetic that the organization in Canada that has been willing to help save this Muslim family is a Jewish organization. Perhaps, in the midst of all the horrible antisemitism that has blossomed in the world over the past years, this provide a useful example that religious differences need not always be a source of discord and hatred.

That was 18 months ago. In spite of having fulfilled at the requirements, the backlog of cases is such that we knew it could take up to two years for the application to be processed. In the interim the family was able to travel to Pakistan. But their visas have expired and Pakistan is now deporting Afghan refugees back to Afghanistan.

The family is in hiding in Pakistan, not able to leave their house. The girls are growing and one of them managed to learn enough English to get a prized scholarship to study online at a US university abroad, where she is studying psychology, as the law degree that she really wants is not available.

The family agreed to be interviewed for this podcast. Their images have been washed out for their protection, and their names have been changed as well. We are hoping this podcast will help spur some of you to provide support through Claire’s online site to help provide essentials for the family while they are in hiding, and that it might also help motivate some of you who might live in Canada to help us lobby the government to ensure that their case is resolved as quickly as possible.

Thanks for watching, or listening, and for any help you can provide. Here is a gofundme link to help support them. https://www.gofundme.com/f/please-help-five-afghan-girls-get-to-safety

As always, an ad-free video version of this podcast is also available to paid Critical Mass subscribers. Your subscriptions support the non-profit Origins Project Foundation, which produces the podcast. The audio version is available free on the Critical Mass site and on all podcast sites, and the video version will also be available on the Origins Project YouTube.