> For instance, the fact that the laws of physics are the same today as they were yesterday and will be tomorrow — a symmetry known as time translation symmetry, represented by the Lie group consisting of the real numbers — implies that the universe’s energy must be conserved, and vice versa. “I think, even now, it’s a very surprising result,” Alekseev said.
Maybe I’m misunderstanding the implication here but wouldn’t it be much more surprising if that weren’t the case?
The surprising thing isn’t that physics remain the same from one day to another, it’s that that fact is the reason for conservation of energy. There are lots of different symmetries for the laws of physics: the laws don’t change from one day to another, they don’t change from one part of the universe to the next, and they don’t change based on angles (e.g. if you snapped your fingers and rotated the entire universe by 10 degrees around some arbitrary point, the universe would continue exactly the same as before, just 10 degrees rotated). From Noether’s theorem, you can take any symmetry on the laws of physics, and use that to derive a conservation law. In those examples, that gives you conservation of energy, conservation of momentum, and conservation of angular momentum, respectively.
It is surprising only when you are not aware of the right definition of energy.
The energy is a ratio between "action" and time, where "action" is a primitive quantity that does not depend on the system of coordinates.
While energy can be computed with various other formulae, like the product of force by length, all the other formulae obscure the meaning of energy, because they contain non-primitive quantities that depend themselves on time and length.
So energy depends directly on time, thus the properties of time transfer to properties of energy.
Similarly, the momentum is a ratio between "action" and length, so the symmetry properties of space transfer to properties of momentum, resulting in its conservation.
The same for the angular momentum, which is a ratio between "action" and phase (plane angle of rotation).
> For instance, the fact that the laws of physics are the same today as they were yesterday and will be tomorrow
Don’t we just commonly assume this axiomatically but there’s no evidence one way or the other? In fact, I thought we have observations that indicate that the physics of the early universe is different than it is today. At the very least there’s hints that “constants” are not and wouldn’t that count as changing physics.
It is surprising that you can derive conversation laws entirely from the symmetry of lie groups, and that every conservation law can be tied to a symmetry.
What "loses energy" actually means here depends on what kind of redshift you're talking about.
If you're talking about gravitational redshift, because the light is climbing out of the gravity well of a planet or star, there actually is a conserved energy involved--but it's not the one you're thinking of. In this case, there is a time translation symmetry involved (at least if we consider the planet or star to be an isolated system), and the associated conserved energy, from Noether's Theorem, is called "energy at infinity". But, as the name implies, only an observer at rest at infinity will actually measure the light's energy to be that value. An observer at rest at a finite altitude will measure a different value, which decreases with altitude (and approaches the energy at infinity as a limit). So when we say the light "redshifts" in climbing out of the gravity well, what we actually mean is that observers at higher altitudes measure its energy (or frequency) to be lower. In other words, the "energy" that changes with altitude isn't a property of the light alone; it's a property of the interaction of the light with the observer and their measuring device.
If you're talking about cosmological redshifts, due to the expansion of the universe, here there's no time translation symmetry involved and therefore Noether's Theorem doesn't apply and there is indeed no conserved energy at all. But even in this case, the redshift is not a property of the light alone; it's a property of the interaction of the light with a particular reference class of observers (the "comoving" observers who always see the universe as homogeneous and isotropic).
Edit: I just looked into this & there are a few explanations for what is going on. Both general relativity & quantum mechanics are incomplete theories but there are several explanations that account for the seeming losses that seem reasonable to me.
1. Lie groups describe local symmetries. Nothing about the global system
2. From a SR point of view, energy in one reference frame does not have to match energy in another reference frame. Just that in each of those reference frames, the energy is conserved.
3. The conservation/constraint in GR is not energy but the divergence of the stress-energy tensor. The "lost" energy of the photo goes into other elements of the tensor.
4. You can get some global conservations when space time exhibits global symmetries. This doesn't apply to an expanding universe. This does apply to non rotating, non charged black holes. Local symmetries still hold.
The consequence of Noether's theorem is that if a system is time symmetric then energy is conserved. On a global perspective, the universe isn't time symmetric. It has a beginning and an expansion through time. This isn't reversible so energy isn't conserved.
Please explain. Noether's theorem equates global symmetry laws with local conservation laws. The universe does not in fact have global symmetry across time.
You are making the same mistake as OP. Formal models and their associated ontology are not equivalent to reality. If you don't think conservation principles are valid then write a paper & win a prize instead of telling me you know for a fact that there are no global symmetries.
The typical example people use to illustrate that energy isn't conserved is that photons get red-shifted and lose energy in an expanding universe. See this excellent Veritasium video [0].
But there's a much more striking example that highlights just how badly energy conservation can be violated. It's called cosmic inflation. General relativity predicts that if empty space in a 'false vacuum' state will expand exponentially. A false vacuum occurs if empty space has excess energy, which can happen in quantum field theory. But if empty space has excess energy, and more space is being created by expansion, then new energy is being created out of nothing at an exponential rate!
Inflation is currently the best model for what happened before the Big Bang. Space expanded until the false vacuum state decayed, releasing all this free energy to create the big bang.
Alan Guth's book, The Inflationary Universe, is a great book on the topic that is very readable.
That symmetries imply conservation laws is pretty fascinating (see the Noether theorem). I guess it seems only strange it you assume already that the conservation law holds.
The way I read this is that there are many "games" in life (applying for schools, jobs, dating, etc) where the odds of "winning" each instance are not in your favor, but you only need to win once to win overall. If you treat every absence of a positive outcome as a failure, then you're inevitably going to lose hope and give up.
This is in contrast to gambling where you actually do need to win more often than not to win overall.
Seems like a momumental waste of energy being pushed as "hustling". Applying to college should be cooperative between you and the admissions office: asking, are we a good fit? Applying in the hope they mess up and admit you when they're really better off rejecting you is so antisocial.
Admissions are sort-of Pareto distributed, so most people admitted were on the edge of being rejected. Since there is a bit of noise in the process, this is why any one individual applying to 10x as many places of a similar tier will be more likely to get into one. But then when everyone does it, no one is more or less likely to get in except those that are actually cooperating with the admissions office. You're burning down the commons for a fleeting bit of warmth. Might I suggest installing a furnace in your house instead?
All I can say is that the method works specifically because people like you exist. It kind of defeats the purpose if we try to change your mind about this.
Lol, yes. If you're a selfish egoist, you probably don't want to convert others to your philosophy.
I think it's possible to punish people who are taking these selfish actions, and I think universities should. Maybe they should make a secret database where they list the people who applied to their university, and subtract off points for every other university they applied to. Or, recruiting agencies can mark down candidates for every other job they are applying to. I don't think they do, and this isn't the startup I want to make or area I want to devote my life to, it just sucks that people are being rewarded for playing negative-sum games.
> Applying in the hope they mess up and admit you when they're really better off rejecting you is so antisocial.
What? That's not what I'm suggesting at all. I just found the post to be a helpful reminder of how to have a healthy mindset towards some uncertainties in life, but it seems like you took away something completely different.
What do you mean by "a healthy mindset"? It isn't healthy for society. It isn't healthy in the world where everyone has this mindset. It isn't healthy to treat your life as a lottery, hoping for a winning ticket instead of creating that ticket yourself. The fact that you consider applications to be uncertainties in life is very telling. You can make them much less uncertain, if you stop thinking of them like a lottery and start doing the things that prove you are valuable to others.
Did you know that USAMO qualifiers have >50% rate of admission to MIT? IMO gold medalists have >80% acceptance rate, and it's only so low because international admissions is limited to 10% of the student body. Life is only a lottery if you have an unhealthy mindset holding you back from improving yourself. Just because university admissions involve a lot of luck at the bottom does not mean you have to limit yourself to a bottom feeder spraying and praying to get in.
Again, I think you've completely misinterpreted the post as well as what I'm trying to say. A "healthy mindset" is simply one that gives you a framework to navigate the world without falling into despair when things don't go your way. Learning to accept that things won't always go your way, and that in some cases they might not go your way the majority of the time, but that they don't have to, is one component of that.
I'm not making any recommendations on how people should actually go about finding wealth, or success, or happiness, or whatever it is you're looking for in life; only how to deal with it when they don't get those things immediately.
Again, I think you don't understand: your "healthy mindset" here is a vice. I do not think it is healthy to drink away your woes. I also do not think it is healthy to cope by treating your life like a big lottery. As I have said several times, the reason I do not consider it healthy is it does not actually help you get what you want, and statistically will leave most people worse off. Finally, from a societal perspective, just like drunk driving hurts everyone around you, this coping behavior also hurts everyone around you.
I would be okay with people spreading beliefs that only hold themselves back, especially if it made them happier. However, I draw the line when they endorse antisocial behavior. I've personally been negatively effected by these hustlers' acions. Almost everyone has, whether or not they can articulate why it seems impossible to get interviewed for a job these days.
I'm not at all advocating for treating life like a lottery. I've had overall a successful career due in large part to my own effort, but the best opportunities have come to me simply by being in the right place at the right time, so it would be arrogant to discount luck entirely. I've also had periods of repeated failure, and if I had counted each and every one of those as a score against my own value then I wouldn't have made it this far. Put more simply, the healthy mindset I have is to do what you can, and accept what you can't. Sometimes things work out, sometimes they don't. Easier said than done.
It seems like you're misinterpreting my words through the lens of your own frustrations right now, so I don't think there's anything else I can say to help you. I just hope you find what you're looking for eventually.
You are not even talking about the article at this point. "All it takes is for one to work out" is TFT. You are instead saying, "be stoic in the things you cannot effect." The latter is much more defensible, and something I endorse. But if you hold the latter, then all it takes is for none to work out. You would accept none, even if you would prefer one, two, or ten. Your comment is a classic motte-and-bailey defense.
> Based on the man page it doesn’t appear to be doing anything useful here
The man page tells me:
-S, --split-string=S
process and split S into separate arguments; used to pass multi‐
ple arguments on shebang lines
Without that, the system may try to treat the entirety of "uv run --script" as the program name, and fail to find it. Depending on your env implementation and/or your shell, this may not be needed.
Without -S, `uv run --script` would be treated as a binary name (including spaces) and you will get an error like "env: ‘uv run --script’: No such file or directory".
-S causes the string to be split on spaces and so the arguments are passed correctly.
This actually looks perfect for me. I travel often with my steam deck, and sometimes pack an xbox controller or two to play local multiplayer with friends but this is a much less bulky alternative.
Even if Python used the anonymous function syntax proposed, people would still call them "lambdas". If you want to have aa keyword for this, you might as well name it after what most people are going to type into Google when searching for it.
Not necessarily. In Perl we called lambda "anonymous sub" for ages, and nobody mixed those up. We also use a handy keyword less syntax to generate, store and use such lambda's. Thus I'm on the "Worse is Better" side, python cannot write proper compilers and cannot decide on proper syntax.
I really despise the idea that we should let the manufacturer decide what's best for us with no out based on the premise of protecting people who don't know any better. As technology becomes an increasingly integral part of our lives, people need to be able to think for themselves and understand the consequences of how they interact with software.
Also as someone who's grandmother started her own software company and was a programmer since the days of punchcards, I find these "what about grandma" appeals very repetitive and kind of insulting.
> Also as someone who's grandmother started her own software company and was a programmer since the days of punchcards, I find these "what about grandma" appeals very repetitive and kind of insulting.
Your grandmother sounds like a genuinely very impressive person, given that it would have been a much more difficult career to forge as a woman in the timeframe from punchcards forward, even up to the present day.
Respectfully, I don't believe you are insulted. I think you know what was meant by the above, and chose to be insulted.
Your overall argument is also not wrong, but kind of irrelevant. This is HN - everyone here is a tech enthusiast. We are not Apple's target market. Removing the guardrails would cost them revenue and headaches.
Whether or not companies should be made to allow arbitrary software to run on devices is a different question entirely, has no clear and simple answer, and I'm not sure who would have the authority to make that happen.
On the other hand, my grandma could barely use a DVD player, and definitely didn't want to learn to set one up. But when the industry bullied her into getting DVDs by making VHS too flimsy to last more than 10 years and then ditching it... she got us in to fix her problem.
"Grandma" doesn't mean "grandma" in these discussions, it's a placeholder for "people not driven to learn the details of all of their tools". Which is most people. Some people do "people" or "animals" or "geology" and not "technology". Your grandma sounds ace, btw.
It sounded like the underlying issue was the OS reusing the same int value for the file descriptor (2), rather than a dangling FILE*, which AFIK is not something rust could prevent. The only way you could really prevent this is if the OS generated GUIDs for newly opened files.
I’ve spent countless hours playing insta-team on Venice. Any Linux distro which doesn’t include Sauerbraten in its package repo isn’t one worth using, IMO
Maybe I’m misunderstanding the implication here but wouldn’t it be much more surprising if that weren’t the case?
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