We kick off our informal video series on The Biggest Ideas in the Universe with one of my favorites — Conservation, as in “conservation of momentum,” “conservation of energy,” things like that. Readers of The Big Picture will recognize this as one of my favorite themes, and smile with familiarity as we mention some important names — Aristotle, Ibn Sina, Galileo, Laplace, and others.
The Biggest Ideas in the Universe | 1. Conservation
Remember that for the next couple of days you are encouraged to leave questions about what was discussed in the video, either here or directly at the YouTube page. I will pick some of my favorites and make another video giving some answers.
Update: here’s the Q&A.
The Biggest Ideas in the Universe | Q&A 1 - Conservation
Could you discuss entanglement and Quantum Darwinism with regards to many worlds, and perhaps interview Wojiciech Kurek on Mindscape? Thanks, I enjoy mindscape!
Might want to clarify that it’s questions relevant to the video. :p
I’m a little confused about the inelastic collisions. I get that momentum is a vector quantity and so if we look at the whole system then +ve and -ve vectors would cancel out but if we just look at a single blob, where does it’s momentum go? How does the cancelling out actually work?
Great idea to do these videos BTW.
Hi Sean, as I see it, the assumption that energy must be conserved, is only valid under the assumption that the Universe is an enclosed system (i.e. no energy can be added or removed from it).
Why are we assuming that?
Tegmark even writes in his “Many worlds or many words”: “Corollary 1: the entire Universe evolves according to the Schrödinger equation, since it is BY DEFINITION an isolated system.”
Why do we live under that assumption?
Is there any proof or indication that would make us jump to that conclusion?
I believe that it might be dangerous to assume that our Universe under all circumstances resembles “the particle in the box.
(Please don’t mind the Avatar, I did not choose it. I’m a happy person 😄)
Did Newton look up Galileo’s work and did Galileo look up Avicenna’s work ? Or did they build their ideas independently ? Curious to know whether history of physics could have gone any other way ? Is it necessary for theory of gravity to develop after law of conservation of momentum? Thank you.
Great lecture.
As I learnt it a few years ago, Aristotle appears to have made the point you attribute to Avicenna. Namely, that vacuum can not exist. Otherwise things kept moving.
It is generally accepted that energy is not conserved in an expanding spacetime. Some physicists have made claims that used pseudo tensors there exist calculations where energy conservation can demonstrated in an expanding space time. But as I understand it, there is a pretty strong consensus that rejects these assertions. It’s actually quite easy to see why energy isn’t conserved in an expanding universe without getting into the difficult formalism of General Relativity when for example you consider radiation and dark energy. In fact any form of mass energy with a non zero equation of state parameter seems to violate energy conservation. However, there is an equally strong consensus that if the universe is finite , not only is energy conserved, the total energy is zero due to negative gravitational energy. Is there a fairly simple intuitive way to understand this?
Can please eloborate more on inelastic collision!!
I previously asked you to tackle the question of whether the Core Theory was a useful argument for a deterministic universe. I just went back and re-read your excellent, comprehensive post of Dec. 5, 2011 – “On Determinism.”
https://www.preposterousuniverse.com/blog/2011/12/05/on-determinism/
So now I’m amending my question to the following: Since that 2011 post, have their been any changes in your thinking on the topic, or does it still stand in tact? If there are no new clarifications or updates, I’m fine with you disregarding my question. Thanks. (Thoroughly enjoyed the first installment.)
Entanglement would be a nice topic to hear you tangle with. Somehow it slipped out of the theory books onto the workbench without a nuts and bolts framework to help most of us understand the internet devices they are building with it
Thank you Sean. I am not a scientist but love science. I have enjoyed your books. You explain things in a way I can understand. You are a worthy recipient of the spherical cow award.
The thoughts conveyed in your initial post brought both a feeling of relaxation & excitation to my mind. Looking at generalizations, trends and connections between a wide variety of subject matter has always piqued my imagination. With the simple principles of conservation of momentum and energy you discussed, can you describe a few practical applications that may be encountered in every day life that involve the use of these principles? Although John Nash found economic implications for the “game theory” he described in great detail, aren’t there fundamental physics involved in the processes he studied?
With respect to conservation of energy in an expanding universe, it is my understanding that conservation of energy in relativity is strictly a local phenomenon. It is generally stated as, given a neighborhood of a point in space-time, the integral of energy flux over the border of that neighborhood will be zero. Restated, if you have a volume of space over a period of time, the amount of energy in that volume at the end of the period will be equal to the amount of energy at the beginning of the period, plus the amount of energy that entered the volume (which could be positive or negative).
Hello Sean. I think you mentioned that objects move at a constant velocity in a vacuum. What is the value of that velocity ? What does the velocity depend on? I am particularly interested the the Voyager spacecrafts which I understand will simply continue at some velocity? forever. What is that velocity or does everything move at the same velocity ?? Hope that makes some sense. Enjoyed the first video. Thanks.
Physics in a Box & Physics of a Box: Emergence, Idealization and the Spherical Cow in AI
Because “it is so much easier to make progress in physics” than in complex (emergent) systems, we have to wonder to what extent deterministic classical laws are (highly compressed) conceptual artifacts of tightly constrained (idealized), isolated, closed systems (the Spherical Cow). The use of physics integrated into AI and autonomous machine learning strategies to study complex systems like economics and ecology seems to be pointing back to Aristotle a bit in that the “Agency” of individual constituents of complex systems, which are themselves complex systems (e.g., organisms), seems to require inclusion of certain behavioral aspects such as purpose, intent, expectation, and “natural tendency”. These systems do not seem to “reduce” to fundamental physics, and are not easily synthesized (in a formal predictive way) from fundamental constituents. I think it would be very helpful, especially because we are faced with not working face-to-face, to cover the big issue of the physics of emergence: how do novel new systems and behavior (like novel SARS Covid 2) evolve from fundamental laws?
Thank you for an interesting presentation, and for your kind gesture at this difficult time. I have two comments on the discussion.
First, I believe that there is a teleological potential even with a purely clockwork universe; not inherent in nature, as Aristotle thought, but overarching. Clockmakers make clocks because they are useful and have a purpose. There are also examples of teleology inherent in nature, such as the numerous examples of symbiotic relationships, many involving plants and organisms of minimal intelligence. I think you might be oversimplifying in this regard (one spherical cow too many!)
Second, while Aristotle was clearly wrong about the world requiring a prime mover, even with our current science-based understanding of the cosmos, we still have no clue about a prime cause.
Hi Sean, I hope this find you and yours well. Will you discuss The Noether Theorems at some point? The increasing mathematization of physics is of interest to me. I recall Maxwell trying to “explain” his math by creating a series of interconnecting cogs. Even Einstein had a “physical intuition” of elevators, no? But these days physical intuitions seem not to be the way to go (e.g. string theory/GR via the graviton — no elevators necessary). Did QM change the game in a big way in this regard? Thank you for your elegant explanations to those of us who appreciate the deep questions of physics but do not have the background (especially math) to understand them. Peace. Bill Harnew
Just FYI, Looking up on Amazon, they have spherical cow T shirts, coffee mugs with spherical cows on them, and there’s even a music group called Spherical Cow.
They also have a book, Consider a Cylindrical Cow, but I assume that involves higher math.
Thanks for your video series!
How did du Chatelet get from ‘the amount of deformation of the surface depends on the kinetic energy of the impacting object’ to ‘energy is conserved’?
What’s the relationship between symmetries of action and the principle of least action?
Would symmetries of quantities other than action lead to other kinds of conservation?
Thanks for the lecture series Sean! Some basic topics that bother me:
1. Energy-time uncertainty principle
2. Is rotation absolute (Mach’s)
Aristotle and Teeth – a (very good) Quora answer
https://www.quora.com/Why-did-Aristotle-think-that-women-had-fewer-teeth-than-men?share=1
Spencer Alexander McDaniel, B.A. Classical Studies & History, Indiana University Bloomington (2022)
Answered Mar 9
Of all the things Aristotle wrote, one of the things he is most often criticized for is the claim that males have more teeth than females. Aristotle writes in his History of Animals 509b (2.3.13):
“Ἔχουσι δὲ πλείους οἱ ἄρρενες τῶν θηλειῶν ὀδόντας καὶ ἐν ἀνθρώποις καὶ ἐπὶ προβάτων καὶ αἰγῶν καὶ ὑῶν· ἐπὶ δὲ τῶν ἄλλων οὐ τεθεώρηταί πω.”
This means, in my own translation:
“And the males have more teeth than the females in humans, in sheep, in goats, and in swine; and in the other species the observation has not been made yet.”
As most people already know, this claim is incorrect; men have exactly the same number of teeth as women.
Aristotle has been lambasted for reporting this false information. The British philosopher Bertrand Russell is particularly known for mocking Aristotle’s claim about women having fewer teeth than men. Russell wrote in his book The Impact of Science on Society, originally published in 1952:
“Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occurred to him to verify this statement by examining his wives’ mouths.”
The textbook Ancient Greece: A Political, Social, and Cultural History by Pomeroy et al. turns Russell’s comment about Aristotle and women’s teeth into a savage burn about Aristotle’s views on women:
“At times, Aristotle’s powers of observation deserted him when women were their subject. The twentieth-century philosopher Bertrand Russell quipped that Aristotle would not have claimed that women had fewer teeth than men if he had allowed his wife to open her mouth” (page 401 in the fourth edition).
Aristotle’s critics are certainly correct that he could have easily checked to verify whether women really had fewer teeth than men. Nonetheless, I think much of this criticism is rather unfair. Aristotle is routinely portrayed as an overconfident buffoon, but he was clearly relying on a report he had heard from someone else that he thought was based on observation. Aristotle evidently assumed that the report was correct and did not bother to verify it for himself.
Now, we might blame Aristotle for not bothering to verify the report himself, but, honestly, I don’t really blame him for not asking his wife to open her mouth so he could count how many teeth she had. After all, looking in someone else’s mouth and counting their teeth is really weird. I can only imagine how awkward that would be, both for Aristotle and for his wife.
Indeed, I seriously doubt that Bertrand Russell personally counted his own teeth and his wife’s teeth to make sure that they really had the same number of teeth. I strongly suspect Russell did exactly the same thing as Aristotle; he heard a report that men and women had the same number of teeth and he assumed that it was true.
The only real difference between Aristotle and Bertrand Russell in this regard is that the report Russell heard happened to be correct and the report Aristotle heard happened to be wrong.
It’s also worth noting here that Peter Gainsford, a classicist from New Zealand, went through and fact-checked every single statement in Aristotle’s chapter on teeth and found that Aristotle was actually correct the vast majority of the time. Aristotle got stuff wrong occasionally, but, when it comes to science, he was actually right far more often than he was wrong.
I’ve heard you mention a few times now (in talks and in The Big Picture) that the realization that things would continue to move forever at a constant rate in a vacuum was somehow relevant to how Aristotle or medieval theists would have viewed God. But didn’t Aristotle specifically argue that there was a prime mover? Not that God was out there pushing every object at every moment, but that he provided the initial push. Even knowing Newton’s 1st Law, we still don’t have any explanation for why any objects were in motion to begin with. We only know why they stay in motion after the original push.
Hi Sean, I’ve enjoyed your posts over the years (preposterousuniverse in particular). This is my first question ever, and I’ve signed on to Patreon just to be sure I have more access to you 😉
Regarding your CONSERVATION – Symmetries lecture:
How do you account for symmetries/conservation in our (closed) universe in light of the Second Law of Thermodynamics? (This law always seemed to be unbalanced or incomplete to me.) LIFE and EVOLUTION seem to run in the opposite direction of entropy. Yes, cases are made that entropy is spurred on by evolution of life, but shouldn’t there be a measurable symmetry/conservation there? Are we sure that we are measuring the total states correctly of a differentiated process, ie, my thoughts, a novel, a new movie, the massive amounts of data humans store, etc.) Shouldn’t we be able to symmetrically link those to entropy?
Thanks,
Tony
PS – Also, I suspect ‘time’ links those as well somehow, but that’s just my intuition.
PPS- I would also venture to state that the above evolutionary process is somewhat teleological, and a nature of our universe. LIFE (and it’s increasing evolution) is part of the inherent built in potential/emergent properties of our universe.
What a delicious way teaching Physics.
We learned Physics like parrots – our teachers had no time to discuss conceptual underpinnings. You are sitting with me one to one, you are with your Tablet and I am with my Tablet. Your idea of writing rather than Power Point slides is most appreciated.
Sir, in your part 1 you forgot to define energy as force x distance and derive 1/2 mv2 from that. Instead you plucked 1/2 mv2 from nowhere.
Please correct me if I am wrong.
Thanks