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Acrofales
Spain18284 Posts
Anyway, I suspect you're right. Although you're talking about minor increases to G. If G is too large then everything just clumps together and implodes immediately after the big bang. E: as for life under a minor increase of G, planets that can hold onto an atmosphere but don't have completely crushing conditions at ground level are smaller. Perhaps too small to have a liquid core for long enough for life to flourish (think Mars). | ||
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Vivax
22305 Posts
On April 12 2020 19:38 Simberto wrote: So, my wife just brought home an energy drink called "Maximum G". And i got to wondering: What would change in a universe where the gravitational constant G is larger? I would like to have a strict no google discussion about this, if people are interested. My thoughts so far: Probably nothing changes at the elemental level, as gravitational forces are neglectable there anyways. But (main sequence) stars of the same size should burn hotter and thus burn out quicker. Also, more black holes, because smaller stars can form a black hole now. I have no idea how that would influence other things, especially life. What else would an increased gravitational constant change? Literally out of my bum: Closer bodies and/or higher average mass? | ||
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Simberto
Germany11824 Posts
On April 12 2020 20:09 Acrofales wrote: A strict, no Google discussion. The best way to have uninformed nonsense talks! Well yes, that is exactly what i want! And you are correct, i didn't even think about cosmology, really interesting! I am not certain if the smaller planets are necessarily a problem. Considering how well humans, who developed under 1g deal with different accelerations, my guess would be that the range of gravitational accelerations under which life can develop is pretty wide. Also, i think we don't really need a molten core, as long as we are in the correct distance to the star to have good temperatures. But i think we still have less time for life on planets, because the stars of a given size burn faster now. This does two things: It shifts the habiltable zone outwards (because the star is hotter), and it means that they don't last as long. Smaller stars which last longer may not even be able to have reasonably sized planets in their habitable zone, because that habitable zone might be so far away that the planets are not as tightly bound to the star and might get stolen by other passing stuff. Maybe we also get larger stars on average, because stuff clumps more under higher G? Larger stars are bad, because they are hot and burn out very quickly. Larger stars and more black holes would mean a greatly decreased lifespan of the universe in general, too, even if we don't have the gigantic collapse. | ||
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Vivax
22305 Posts
that said yes, things would be hotter, but i blindly guess with the nass to compensate they wouldnt burn out quicker | ||
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Acrofales
Spain18284 Posts
On April 12 2020 20:38 Simberto wrote: Well yes, that is exactly what i want! And you are correct, i didn't even think about cosmology, really interesting! I am not certain if the smaller planets are necessarily a problem. Considering how well humans, who developed under 1g deal with different accelerations, my guess would be that the range of gravitational accelerations under which life can develop is pretty wide. Also, i think we don't really need a molten core, as long as we are in the correct distance to the star to have good temperatures. I seem to recall a liquid core being a necessary condition. I don't quite recall why. Part of it is because volcanic vents are where life probably started on earth, and maybe that is necessary? Another is that plate tectonics recycle land mass (and that does something that I don't remember anymore). On the other hand, Io has a liquid core because of gravitational forces ripping it apart any time it starts to solidify. While Io is one of the least hospitable places in our solar system, there may be a goldilocks zone for moons of gas giants where liquid water, a molten core and an atmosphere can all exist together? But i think we still have less time for life on planets, because the stars of a given size burn faster now. This does two things: It shifts the habiltable zone outwards (because the star is hotter), and it means that they don't last as long. Smaller stars which last longer may not even be able to have reasonably sized planets in their habitable zone, because that habitable zone might be so far away that the planets are not as tightly bound to the star and might get stolen by other passing stuff. Maybe we also get larger stars on average, because stuff clumps more under higher G? Larger stars are bad, because they are hot and burn out very quickly. Larger stars and more black holes would mean a greatly decreased lifespan of the universe in general, too, even if we don't have the gigantic collapse. I seem to recall that stars that burn hotter are a lot more lethal too: I think it was something about the mix of energy they emit is further into the ultraviolet spectrum. So even if you hang out further away from these stars they may still not be conductive to life. But I can't google and am not 100% sure on my memory of this. It was some sciam article theorizing about what life could look like in different solar systems (with different types of stars). Red giants would be pretty okay if I recall. Given that our sun is projected to explode into a red giant at the end of its lifespan, would a higher G cause more red giants? Or fewer? | ||
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Simberto
Germany11824 Posts
On April 12 2020 20:49 Vivax wrote: doesnt higher g compress things? Also is caused by higher mass and higher mass means more molecules so a star would last longer. less dispersion and more molecules. possibly also more reactive due to proximity and mass. thats when youd need a law to estimate the prevailing effect faster reactions and greater amount. that said yes, things would be hotter, but i blindly guess with the nass to compensate they wouldnt burn out quicker G, not g. g is the gravitational acceleration on the surface of earth. G is the universal gravitational constant that influences how strong the gravitational pull between any two items is. None of them influence the amount of mass, but a higher G would influence the average size of stars building. However, stars are weird. Bigger stars, counter to what your intuition might suggest, actually burn out quicker than smaller stars, because more fusion happens at once, making them hotter and leading to them consuming their fuel faster. So even though they have more fuel (hydrogen in main sequence stars) to start with, they still run out faster. So contrary to what you expect, the stars with the highest lifespan are the smallest, darkest, reddest stars. (Talking main sequence again, red giants work differently). In stars, there generally are no molecules, because they are too hot. You mostly have a hydrogen plasma at the core of stars. If we increase G, we have two effects. Firstly, stars will be larger on average, leading to them burning out quicker. And secondly, stars of the same mass would burn hotter, because the temperature of a stars core depends on an equilibrium between gravitational force and the heat pressure. Both of these effects mean that stars burn out quicker on average However, we might also have a totally new class of stars. Stuff that is currently not massive enough to support fusion, brown dwarfs. Some of these might be really tiny red dwarfs now. I seem to recall a liquid core being a necessary condition. I don't quite recall why. Part of it is because volcanic vents are where life probably started on earth, and maybe that is necessary? Another is that plate tectonics recycle land mass (and that does something that I don't remember anymore). On the other hand, Io has a liquid core because of gravitational forces ripping it apart any time it starts to solidify. While Io is one of the least hospitable places in our solar system, there may be a goldilocks zone for moons of gas giants where liquid water, a molten core and an atmosphere can all exist together? Sounds reasonable. I mean, life on moons of gas giants is pretty awesome, so i like this idea. Just imagine looking up at the sky and seeing a sun, a giant jupiter, and a bunch of other moons. Possibly a ring, too. I don't know if a moon which is close enough to a gas giant for the tidal forces to keep it liquid could keep an atmosphere, though. My rough guess would be that the same forces simply strip of the atmosphere. Of course, the constant volcanoes create new atmosphere, too. Hm. I am generally a fan of this idea, though, just due to the awesomeness of it. I seem to recall that stars that burn hotter are a lot more lethal too: I think it was something about the mix of energy they emit is further into the ultraviolet spectrum. So even if you hang out further away from these stars they may still not be conductive to life. But I can't google and am not 100% sure on my memory of this. It was some sciam article theorizing about what life could look like in different solar systems (with different types of stars). Red giants would be pretty okay if I recall. Given that our sun is projected to explode into a red giant at the end of its lifespan, would a higher G cause more red giants? Or fewer? Good point. The hotter a star is, the further the spectrum shifts towards high-energy radiation (this means that the stars get bluer to the visible eye), and UV is bad for life. I was mostly thinking about the colder edge of stars. Red dwarfs might be yellow like the sun now, and brown dwarfs might start fusion and be red. I don't know about the amount of red giants. Red giants generally don't last long anyways, iirc. Red giant is the stage of a main sequence star that is massive enough to ignite helium fusion after hydrogen fusion is over. (As opposed to the standard hydrogen fusion). My guess would be that higher G just shifts this down the ladder a bit. So some of the stars which might become red giants now do other stuff (I think neutron star, but i don't remember if that is what directly happened to the heavier stars, or if they did something else first), while some of the stars which currently aren't massive enough to support hydrogen fusion might be able to do so under higher G. I don't know about life around red giants in general, though. Red means not a lot of UV, so that is good. But red giants don't last a long time, and they are at the end of the lifespan of a star, so if the molten core is indeed necessary, that would be mostly frozen due to lots of time having happened. | ||
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Vivax
22305 Posts
None of them influence the amount of mass, but a higher G would influence the average size of stars building. However, stars are weird. Bigger stars, counter to what your intuition might suggest, actually burn out quicker than smaller stars, because more fusion happens at once, making them hotter and leading to them consuming their fuel faster. So even though they have more fuel (hydrogen in main sequence stars) to start with, they still run out faster. I always assume atoms are more reactive the closer they are to each other, since they 'tremble' spontaneously, and having more fuel implies having more mass, which I think is the parameter that would have to change first to have higher G. The size of the star would influence how much energy leaves the system as opposed to remaining in it (the dispersion) just by having a bigger surface. In that sense I'd expect bigger stars to have slow reactions with high dispersion, small stars fast reactions with little dispersion, making them better at conserving their energy. Isn't a black hole the result of a star eliminating dispersion by minimizing size and and maximizing mass because it 'wants' to conserve its energy? Higher G might speed up time though, considering it'd increase the speed at which bodies rotate, possibly entropy? Dunno. | ||
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Simberto
Germany11824 Posts
I have no idea about general relativity and can thus not say anything about how it would be influenced by a change in natural constants. The way stars work is actually pretty cool. Basically, a star starts as a cloud of gas. The gravitational pull of this gas collapses it onto itself. This process heats the star. The heat produces a counterpressure to the gravitational pressure which leads to an equilibrium state. However, the star dissipates heat into the surroundings, thus cooling off, reducing the heat pressure and collapsing further. After a while of this, the pressure at the center of the star is so large that fusion of hydrogen cores into helium cores starts, which produces energy, which once again heats the star and thus provides a counterpressure to the gravitational collapse, once again producing an equilibrium state where the heat created by fusion balances the gravitational pull trying to collapse the star. If the star collapses a bit further, more fusion pushes it apart. If it spreads a bit further, less fusion means less heat, meaning more collapse. This situation is stable as long as there is enough hydrogen to fuse. This phase of the lifetime of a star is the "main sequence" phase. The energy dissipated into the universe is dependent on the surface area of the star, but also on the temperature of its surface. The size and temperature of a star in this phase is directly related to its mass. More massive stars are hotter (which leads to a more "blue" spectrum of light emitted by them), while less massive (and thus smaller) stars are colder, meaning they have a more "red" spectrum. A more massive star has a higher rate of fusion AND emits more energy into space. It does so to a greater rate than its additional mass would allow for fuel. Thus, larger stars live for a shorter period of time, while smaller stars do live longer in the main sequence. What happens to the star after its hydrogen runs out once again depends on how massive they are. Usually there are a few more ever shorter phases of fusion of different elements, leading to an end state of either white dwarf, neutron star, or black hole. Where something ends up depends on a few different pressures counteracting the gravitational pull of its own mass. IIRC, white dwarfs happen when fermi exclusion pressure of electrons (multiple electrons cannot be in the same state at the same time) is enough to counter the gravitational pull, neutron stars if that is not enough, but fermi exclusion of neutrons is, and black holes if nothing is strong enough to counteract the gravitational pull. (I might have an unfair advantage in the "no google" discussion because i studied a bit of physics at university) | ||
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Zambrah
United States7393 Posts
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Uldridge
Belgium5121 Posts
I thought it was something Einstein figured out, through his theory of relativity or something? Isn't that also how he'd found the 'black hole "anomalous" solution'? | ||
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Starlightsun
United States1405 Posts
On April 13 2020 00:55 Zambrah wrote: What’s it like being an enlisted person in the Air Force. Why do they call it the chair force? Supposedly it's more cushy than the other branches. | ||
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Simberto
Germany11824 Posts
On April 13 2020 03:17 Uldridge wrote: Don't people generally need to understand higher level maths before understanding something like G? I thought it was something Einstein figured out, through his theory of relativity or something? Isn't that also how he'd found the 'black hole "anomalous" solution'? Not really. For general relativity and a deeper understanding of gravity, sure. But G itself is just a factor in the newtonian formula for gravitation, which you can understand with 6-8th grade math. And that understanding of gravity works very well unless you go into the weirder stuff. | ||
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AbouSV
Germany1278 Posts
This means, that if G was much higher (or lower), it would not change of the physics we know and compute. It would be different, but still exactly the same. That's pretty magical. | ||
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Acrofales
Spain18284 Posts
On April 13 2020 07:45 AbouSV wrote: We recently changed how units are defined. G is, if I remember correctly, one of the constants from which units are then computed. This means, that if G was much higher (or lower), it would not change of the physics we know and compute. It would be different, but still exactly the same. That's pretty magical. I don't understand. Isn't that exactly what we're talking about? Assuming all of the laws of physics continue exactly the same, but with a higher value for G? And what would change in comparison to the universe we know with "our" value of G. | ||
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AbouSV
Germany1278 Posts
The on I talked about before is basically that we would not notice any 'difference'. Just like if water boils at 50° or 200° (yes, Celcius, obviously! :p). 'Stuff' would happen at different scales, but everything around would be adapted the same way and would work the same. Also, our way of interpreting it would be exactly the same. The other way, that I did not speak about, is the fact that we still don't know about gravity. (side fact, G is one of the constants we know with the least significant numbers, yet it is central to so many thing we do!) So it might be that a different G would change some interactions we still have no idea about, and there, we can literally go to science fiction :D | ||
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Acrofales
Spain18284 Posts
On April 13 2020 17:54 AbouSV wrote: For the specific example of G, I see it two ways: The on I talked about before is basically that we would not notice any 'difference'. Just like if water boils at 50° or 200° (yes, Celcius, obviously! :p). 'Stuff' would happen at different scales, but everything around would be adapted the same way and would work the same. Also, our way of interpreting it would be exactly the same. The other way, that I did not speak about, is the fact that we still don't know about gravity. (side fact, G is one of the constants we know with the least significant numbers, yet it is central to so many thing we do!) So it might be that a different G would change some interactions we still have no idea about, and there, we can literally go to science fiction :D Hm. Interesting. So G is arbitrary and defined by us? I thought it was one of the fundamental physical constants (like the speed of light in a vacuum or the Planck distance). If it's like the temperature in centigrade that water boils at, then I agree nothing changes. You'd have to dig deeper and twiddle the fundamental constant that affects G (and probably quite a few other things). The point about boiling water is a bit weird tho. centigrade scale is *defined* by the freezing point and boiling point of water. So yeah, if we changed up that scale (e.g. use Fahrenheit like the Yanks), nothing changes except for the numbers we use to describe things. However, if instead, some underlying physical law of thermodynamics changed *only and exclusively for water*, our planet (and universe) wouldn't look the same (but only really at a planetary scale downwards, stars would still work in exactly the same way as water has no significant role in cosmology). I thought changing G was like the latter (tinkering with fundamental properties of the universe), but you say it's like the former (changing how we describe the fundamental properties of the universe)? | ||
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Simberto
Germany11824 Posts
We could say that G (when measured in Nm²/kg²) quadruples, but we also double the meaning of kg. Nothing changes, we just use other numbers to describe stuff. I was indeed saying we should do the other thing where physics change, too. Just changing the system of measurement is boring. | ||
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Belisarius
Australia6233 Posts
We know very little about what the early universe looked like, but there's a good chance that a higher G means we don't even get expansion in the first place. Sorry, bl. New save, try again. Even if you assume that goes smoothly and we get some stars, they are probably weird-ass stars. Every single one is a razor-edge balance between gravity and heat, as you said. Yes, some would find a new equilibrium by contracting to burn brighter, but there are a bunch of other things involved that can't adjust like that. Electron degeneracy pressure doesn't change and suddenly supports a lot less matter, and pair instability and photodisintegration come into play much more widely because temps are (probably?) higher. Convection probably works very differently, if it works at all. Everything spins way faster. You're rewriting the entire HR diagram at minimum. This stuff matters because everything we see is the product of at least two stellar life cycles. Even in terms of the "elemental level", almost half the periodic table is generated during supernovae. I think you need even weirder events involving stellar remnants to get much above iron. There's no guarantee that this stuff happens if G is higher. A lot of high mass stars don't even produce supernovae, they just pinch out into black holes. I realise we've banned Google, but I remember there was a good diagram on wiki showing stellar remnants for mass vs metallicity. An alarmingly large portion of the phase space goes straight to a black hole with no ejecta, especially for low metallicity stars in the early universe. If G is larger, a lot more stars probably do this, and that's a ton of extra material gone forever. Importantly, population iii stars were huge and almost pure H/He. If too many of them blink out rather than explode that's probably gg again. I don't know anything about galaxy formation but I would be amazed if it worked the same. This is even before we get to the crazily specific and fragile circumstances for life to form. I could be wrong, but I think I like the universe we've got. | ||
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AbouSV
Germany1278 Posts
On April 13 2020 18:10 Acrofales wrote: Hm. Interesting. So G is arbitrary and defined by us? I thought it was one of the fundamental physical constants (like the speed of light in a vacuum or the Planck distance). If it's like the temperature in centigrade that water boils at, then I agree nothing changes. You'd have to dig deeper and twiddle the fundamental constant that affects G (and probably quite a few other things). The point about boiling water is a bit weird tho. centigrade scale is *defined* by the freezing point and boiling point of water. So yeah, if we changed up that scale (e.g. use Fahrenheit like the Yanks), nothing changes except for the numbers we use to describe things. However, if instead, some underlying physical law of thermodynamics changed *only and exclusively for water*, our planet (and universe) wouldn't look the same (but only really at a planetary scale downwards, stars would still work in exactly the same way as water has no significant role in cosmology). I thought changing G was like the latter (tinkering with fundamental properties of the universe), but you say it's like the former (changing how we describe the fundamental properties of the universe)? Kinda both actually. G is one of the fundamental constants of the Universe, so to speak, indeed. But now (since mid last year) the SI unit system is defined from these constants, not the other way around. So the meter, the second and so one, are defined from some constants that we defined as being exactly the value we give them. Then we measure our units as precisely as possible from them. (This has a couple very interesting benefits, but it is not the current question :p) But from that you can either take the 'boring side' of following Simberto response indeed. From a more fundamental and interesting side I'd have no clue, as gravity is not properly known, and I barely know what there is anyway. | ||
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Harris1st
Germany7180 Posts
On April 11 2020 22:40 Sent. wrote: Is Coronavirus a net positive or negative for the environment? On the one hand people are traveling (burning fuel) less, but on the other they started using all those single-use products like plastic gloves more. I'd say the positives for the enviroment outweigh the negatives by far! With all the oil not used by ships/planes/ cars you could probably make a gazillion more single use gloves and it would still be alright To the G discussion (out of my ass): With a higher G the universe wouldn't have expanded (so far/ way slower) Depending on how much higher G is, you probably could just go back in time and look at the universe a million/ billion/ trillion years ago and have a pretty accurate picture | ||
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