Great show if you can find it. Another show, Connections, is much more popular, and traces the family tree of various inventions. Again, highly recommended!
I miss all those relatively unflashy science programmes. They all have to be a bit over the top and made into rather showy but shallow “event” TV, probably featuring Brian Cox on a mountain or in a desert for some reason.
I'd bet economics. There are magic $/experiment thresholds where it becomes possible for scientists to try something, and one the threshold is crossed a bunch of people explore the same area at the same time.
Take neural nets. FLOPS/$ crosses some magic number so that universities can afford the hardware, and bam; AI everywhere. No obvious theoretical breakthroughs since the 70s, but suddenly the field gets intense due to economics.
Somewhat related: I just read a history of England where it was stated that country parsons had a very, very good living and not much work to do, up until 1850 or so, and many of them devoted their energies to all sorts of useful projects.
Also music. Antonio Vivaldi was a priest, but had a special dispensation that excused him from most of the required duties. Gave him a lot of time to compose music.
Bill Bryson’s a short history of the world is very good on this.
Yes Parsons had a class-based sinecure and several of them made huge contributions to science and society. But the vast majority did or achieved nothing and were a drain on resources.
The first wave of globalisation- caused largely by the US ice trade - where taking ice from lakes meant refrigerated train carriages and ice warehouses in Chicago and new York, and refrigerated ships crossing the Atlantic. Suddenly small farms in England, France and Vermont were competing with Iowa corn fields.
There was a 1870s collapse in food prices and the subsequent collapse in social structures - we simply could not afford to keep indolent parsons, and now their “parsonages” are prized second homes
You make it sound as though the pastoral and spiritual care of their congregations was worthless. In a world where belief in God was widespread and living conditions tough, the value of a parson was not just in their scientific or artistic contributions.
> Parsons had a class-based sinecure and several of them made huge contributions to science and society. But the vast majority did or achieved nothing and were a drain on resources
> Michell was also the first to apply the new mathematics of statistics to astronomy. By studying how the stars are distributed on the sky, he showed that many more stars appear as pairs or groups than could be accounted for by random alignments. He argued that these were real systems of double or multiple stars bound together by their mutual gravity. This was the first evidence for the existence of physical associations of stars.
What is our modern understanding of this? Are there kinds of local clusters you could detect with the naked eye?
This mindfuck struck me too. Could a physicist speak to this? Is a black-hole universe a theoretical possibility because it’s a valid solution, say, of the Einstein field equations? Or is it a possibility simply because it’s not falsifiable?
I believe Penrose and Hawking both like this idea, or rather the idea that black holes spawned "baby universes" [1].
Something is falsifiable if you can think up some empirical test that would refute it. That test doesn't need to be feasible. In the case of black hole universes, such a theory may be falsifiable, but we don't know enough about the composition of black holes to even formulate the tests. I'm not a physicist, but my impression is that falsifiability is less important to physics than the ability for a hypothesis to predict and explain observed phenomena.
I don’t think it’s possible to say. Our current definitions of spacetime is limited to what is in the observable universe. What’s on the other side could be a whole different universe with similar spacetime. Or it could be an infinite void. Or it could literally not exist. Or it could be a vast sea of cream cheese. We don’t know, and according to our current understanding of physics, it is impossible for us to ever know.
Edit: not a physicist by the way, would also love someone who actually knows what they’re talking about to butt in.
You're probably joking, but in case not, I would point out that black holes evaporate quickly at small scales, and cannot be smaller than the Planck length.
One of my pet peeves is this vague idea about the universe being an infinite fractal, universes inside atoms, etc. It's an appealing idea, but it's totally inconsistent with quantum mechanics and the difference between the strength of forces on different length scales.
This is one of those ideas that is so wrong that it is right:
> He reasoned that such particles, emerging from the surface of a star, would have their speed reduced by the star’s gravitational pull, just like projectiles fired upward from the Earth. By measuring the reduction in the speed of the light from a given star, he thought it might be possible to calculate the star’s mass.
>Michell asked himself how large this effect could be. He knew that any projectile must move faster than a certain critical speed to escape from a star’s gravitational embrace. This “escape velocity“ depends only on the size and mass of the star. What would happen if a star’s gravity were so strong that its escape velocity exceeded the speed of light? Michell realized that the light would have to fall back to the surface.
I wouldn't say that. Yes, it's not exactly our modern understanding, but the core idea is the exact same: stars can get big enough that even light, which is super fast, can't escape them, and that was an entirely novel idea in his time.
I think it's more that the effective idea is the same, while the core idea is what is so vastly different. He was arguing as if light was affected by gravity. This is totally missing the rather revolutionary idea of general relativity, best explained by John Wheeler: "Spacetime tells matter how to move; matter tells spacetime how to curve".
Can you say more about what's wrong about it? It seems plain right to me, in Newtonian physics, assuming only that light has a speed (which was not at all a crazy thing to think at that point), and historians of cosmology usually agree (source personal communication, so I could be wrong).
Once you know speed of light is the maximum possible speed, you can try to guess what happens when you have enough mass to make escape velocity higher than the speed of light (it is not possible, therefore you can't escape).
I've never liked the "escape velocity >= c" explanation of why you can't get out a black hole. The escape velocity for a body at a given point is the velocity needed to escape from that point ballistically.
If you don't limit yourself to entirely ballistic trajectories you can escape without ever reaching that point's escape velocity.
To explain why nothing, not even things on non-ballistic trajectories, cannot get out of black holes you've got to turn to weird headache inducing general relativity stuff.
You are correct. It's a fortunate coincidence and nothing more.
It's much easier to think of the gradual warping of spacetime around a black hole so that more and more directions are down. East? No, that's really east and down. Left? Nope, you thought you were going left but it is left and down. Less and less "up" is available to you until you are on a knife edge where you can make an orbit (assuming a non-rotating black hole, no angular momentum) around the event horizon with a photon. Beyond that, everything is some flavor of down.
Well, if you go with Newton's explanation for light, it's quite obvious that it can only follow ballistic trajectories.
One would certainly not expect elementary particles to function like rockets.
But yeah, nobody could come with a description of a black hole anything like the modern one before 1900. Anything older is certain to be very different.
That's right. The Earth's escape velocity is just over 11km/s or 4000km/h. If you have a rocket that only has enough force to propel you at say 100km/h away from the earth you can go anywhere you want in the universe - provided you keep applying that force through thrust. If you stop the rocket you will be subject to gravitational force to bring you back (or until the gravitational pull from other bodies of becomes dominant)
Newton introduced the corpuscular theory of light, in modern terms saying that light is made of tiny particles. Once you have that, it becomes natural to think that light is probably attracted by gravity just like everything else is.
The wave theory of light came quite a bit later, in Maxwell's time.
It's not a question of enough mass. It's a question of being compact enough. There is no minimum mass for a black hole, but the smaller the mass, the smaller the surface area of the horizon (the 2-sphere that the mass has to collapse inside to form the hole).
> Once you know speed of light is the maximum possible speed
But he didn't postulate this at all. He simply postulated (as per Newton) that light is made of particles with mass, which could thus be affected by gravity. Since they are moving at a finite speed, the light particles would be slowed down by gravity, and eventually completely stopped.
He further proposed, based on this model, that the mass of an object could potentially be determined by determining how much slower the particles were moving.
This doesn't work. Light doesn't really get slowed down by gravity, and you definitely don't have any slow light that was created from stars trillions of miles away.
It's a cool idea, but doesn't work with how light actually propagates.
Readit News
Great show if you can find it. Another show, Connections, is much more popular, and traces the family tree of various inventions. Again, highly recommended!
https://archive.org/details/bbc-connections-1978
Hard to believe it's a quarter of a century since it finished.
I miss all those relatively unflashy science programmes. They all have to be a bit over the top and made into rather showy but shallow “event” TV, probably featuring Brian Cox on a mountain or in a desert for some reason.
* Newton and Leibniz with calculus
* Darwin and Wallace with evolution
* all those shared Nobel Prizes by independent scientists (eg: Feynman and Tomonaga/Schwinger with quantum electrodynamics, et al)
Presumably because knowledge converges and the field in question becomes ripe for discovery.
Take neural nets. FLOPS/$ crosses some magic number so that universities can afford the hardware, and bam; AI everywhere. No obvious theoretical breakthroughs since the 70s, but suddenly the field gets intense due to economics.
Then the money dried up, as agriculture changed.
Yes Parsons had a class-based sinecure and several of them made huge contributions to science and society. But the vast majority did or achieved nothing and were a drain on resources.
The first wave of globalisation- caused largely by the US ice trade - where taking ice from lakes meant refrigerated train carriages and ice warehouses in Chicago and new York, and refrigerated ships crossing the Atlantic. Suddenly small farms in England, France and Vermont were competing with Iowa corn fields.
There was a 1870s collapse in food prices and the subsequent collapse in social structures - we simply could not afford to keep indolent parsons, and now their “parsonages” are prized second homes
a drain on whose resources?
What is our modern understanding of this? Are there kinds of local clusters you could detect with the naked eye?
https://arxiv.org/abs/2311.01865
For naked eye clusters look up pleiadis in the northern emisphere and LMC/SMC in the south, and then you can use stellarium (see other HN post)
> ... it is conceivable that our entire observable universe is a supermassive black hole within a larger universe.
Something is falsifiable if you can think up some empirical test that would refute it. That test doesn't need to be feasible. In the case of black hole universes, such a theory may be falsifiable, but we don't know enough about the composition of black holes to even formulate the tests. I'm not a physicist, but my impression is that falsifiability is less important to physics than the ability for a hypothesis to predict and explain observed phenomena.
[1] https://www.salon.com/2020/10/18/why-physics-nobelist-roger-...
Edit: not a physicist by the way, would also love someone who actually knows what they’re talking about to butt in.
One of my pet peeves is this vague idea about the universe being an infinite fractal, universes inside atoms, etc. It's an appealing idea, but it's totally inconsistent with quantum mechanics and the difference between the strength of forces on different length scales.
> He reasoned that such particles, emerging from the surface of a star, would have their speed reduced by the star’s gravitational pull, just like projectiles fired upward from the Earth. By measuring the reduction in the speed of the light from a given star, he thought it might be possible to calculate the star’s mass.
>Michell asked himself how large this effect could be. He knew that any projectile must move faster than a certain critical speed to escape from a star’s gravitational embrace. This “escape velocity“ depends only on the size and mass of the star. What would happen if a star’s gravity were so strong that its escape velocity exceeded the speed of light? Michell realized that the light would have to fall back to the surface.
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If you don't limit yourself to entirely ballistic trajectories you can escape without ever reaching that point's escape velocity.
To explain why nothing, not even things on non-ballistic trajectories, cannot get out of black holes you've got to turn to weird headache inducing general relativity stuff.
It's much easier to think of the gradual warping of spacetime around a black hole so that more and more directions are down. East? No, that's really east and down. Left? Nope, you thought you were going left but it is left and down. Less and less "up" is available to you until you are on a knife edge where you can make an orbit (assuming a non-rotating black hole, no angular momentum) around the event horizon with a photon. Beyond that, everything is some flavor of down.
One would certainly not expect elementary particles to function like rockets.
But yeah, nobody could come with a description of a black hole anything like the modern one before 1900. Anything older is certain to be very different.
Relativity makes black holes much more "final" than this original concept, but he was definitely thinking in the right direction.
The wave theory of light came quite a bit later, in Maxwell's time.
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It's not a question of enough mass. It's a question of being compact enough. There is no minimum mass for a black hole, but the smaller the mass, the smaller the surface area of the horizon (the 2-sphere that the mass has to collapse inside to form the hole).
But he didn't postulate this at all. He simply postulated (as per Newton) that light is made of particles with mass, which could thus be affected by gravity. Since they are moving at a finite speed, the light particles would be slowed down by gravity, and eventually completely stopped.
He further proposed, based on this model, that the mass of an object could potentially be determined by determining how much slower the particles were moving.
This doesn't work. Light doesn't really get slowed down by gravity, and you definitely don't have any slow light that was created from stars trillions of miles away.
It's a cool idea, but doesn't work with how light actually propagates.