# New kinds of Cash & the connection to the Conservation of Energy And Momentum

Its been difficult to find time to write articles on this blog – what with running a section teaching undergraduates (after 27 years of ${\underline {not \: \: doing \: \: so}}$), as well as learning about topological quantum field theory – a topic I always fancied but knew little about.

However, a trip with my daughter brought up something that sparked an interesting answer to questions I got at my undergraduate section. I had taken my daughter to the grocery store – she ran out of the car to go shopping and left her wallet behind. I quickly honked at her and waved, displaying the wallet. She waved back, displaying her phone. And insight struck me – she had the usual gamut of applications on her phone that serve as ways to pay at retailers – who needs a credit card when you have Apple Pay or Google Pay. I clearly hadn’t adopted the Millennial ways of life enough to understand that money comes in yet another form, adapted to your cell phone and aren’t only the kinds of things you can see, smell or Visa!

And that’s the connection to the Law Of Conservation of Energy, in the following way. There were a set of phenomena that Wolfgang Pauli considered in the 1930s – beta decay. The nucleus was known and so were negatively charged electrons (these were called $\beta$-particles). People had a good idea of the composition and mass of the nucleus (as being composed of protons and neutrons), the structure of the atom (with electrons in orbit around the nucleus) and also understood Einstein’s revolutionary conceptions of the unity of mass and energy. Experimenters were studying the phenomenon of nuclear radioactive decay. Here, a nucleus abruptly emits an electron, then turns into a nucleus with one higher proton number and one less neutron number, so roughly the same atomic weight, but with an extra positive charge. This appears to happen spontaneously, but in concert with the “creation” of a proton, an electron is also produced (and emitted from the atom), so the change in the total electric charge is $+1 -1 = 0$ – it is “conserved”.  What seemed to be happening inside the nucleus was, that one of the neutrons was decaying into a proton and an electron. Now, scientists had constructed rather precise devices  to “stop” electrons, thereby measuring their momentum and energy. It was immediately clear that the total energy we started with – the mass-energy of the neutron (which starts out not moving very much in the experiment), in decaying into the proton and electron was more than the energy of the said proton (which also wasn’t moving very much at the end) and aforesaid electron.

People were quite confused about all this. What was happening? Where was the energy going? It wasn’t being lost to heating up the samples (that was possible to check). Maybe the underlying process going on wasn’t that simple? Some people, including some famous physicists, were convinced that the Law of Conservation of Energy and Momentum had to go.

As it turned out, much like I was confused in the car because I had neglected that money could be created and destroyed in an iPhone, people had neglected that energy could be carried away or brought in by invisible particles called neutrinos. It was just a proposal, till they were actually discovered in 1956 through careful experiments.

In fact, as has been rather clear since Emmy Noether discovered the connection between a symmetry and this principle years ago, getting rid of the Law of Conservation of Energy and Momentum is not that easy. It is connected to a belief that physics (and the result of Physics experiments) is the same whether done here, on Pluto or in empty space outside one of the galaxies on the Hubble deep field view! As long as you systematically get rid of all “known” differences at these locations – the gravity and magnetic field of the earth, your noisy cousin next door, the tectonic activity on Pluto, or small black holes in the Universe’s distant past, the fundamental nature of the universe is $translationally \: \: invariant$. So if you discover that you have found some violation of the Law of Conservation of Energy and Momentum, i.e., a perpetual motion machine, remember that you are announcing that there is some deep inequivalence between different points and time in the Universe.

The usual story is that if you notice some “violation” of this Law, you immediately start looking for particles or sources that ate up the missing energy and momentum rather than announce that you are creating or destroying energy. This principle gets carried into the introduction of new forms of “potential energy” too, in physics, as we discover new ways in which the Universe can bamboozle us and reserve energy for later use in so many different ways. Just like you have to add up so many ways you can store money up for later use!

That leads to a conundrum. If the Universe has a finite size and has a finite lifetime, what does it mean to say that all times and points are equivalent? We can deal with the spatial finiteness – after all, the Earth is finite, but all points on it are geographically equivalent, once you account for the rotation axis (which is currently where Antarctica and the Arctic are, but really could be anywhere). But how do you account for the fact that time seems to start from zero? More on this in a future post.

So, before you send me mail telling me you have built a perpetual motion machine, you really have to be Divine and if so, I am expecting some miracles too.