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Re: Science fleeting thoughts

Posted: Thu Apr 18, 2019 1:02 pm UTC
by p1t1o
Sableagle wrote:2) The rounding happens at the end. Rounding everything to 1 s.f. as you go is for figuring out which county you'll be in on Tuesday, not for building model aircraft.


femto-Hertz...

Re: Science fleeting thoughts

Posted: Thu Apr 18, 2019 1:05 pm UTC
by Eebster the Great
There is some room between keeping only one significant figure at each step and keeping 17.

Re: Science fleeting thoughts

Posted: Thu Apr 18, 2019 2:08 pm UTC
by poxic
Eebster the Great wrote:It is not mathematically different from no time dilation at all.

Similar to a thought I'd had that led to deciding I needed to sleep more than to muck about with spacetime.

Re: Science fleeting thoughts

Posted: Fri Apr 19, 2019 5:42 pm UTC
by gmalivuk
Sableagle wrote:1) I wouldn't want to be accused of cutting the numbers short to conceal a "666" in there somewhere.
2) The rounding happens at the end. Rounding everything to 1 s.f. as you go is for figuring out which county you'll be in on Tuesday, not for building model aircraft.

There's a happy medium, and keeping track of a number ten orders of magnitude more precise than the gravitational constant you multiplied to get it is pretty far to one side of it.

Especially when the figure you calculated for G*Mearth managed to be off by two in the fourth digit in any case.

Re: Science fleeting thoughts

Posted: Wed Apr 24, 2019 6:07 am UTC
by Soupspoon
Did the Earth Mars move for you, darling?
Mars quakes! Or gets hit by something, but it's too early to know much more about it.

(Noting that its own arm caused a more definite signal to the disconnected device, according to that image.)

Re: Science fleeting thoughts

Posted: Fri May 03, 2019 11:08 pm UTC
by Sableagle
Anyway, orbit around the Sun.
Perihelion (10^6 km) 147.09
Aphelion (10^6 km) 152.10
Max. orbital velocity (km/s) 30.29
Min. orbital velocity (km/s) 29.29
Tropic radius (km): 6374.895
Tropic linear velocity: 465464.86472922 m/s
Perihelion midday: 1.47 * 10^11147083625105 m.
Perihelion midnight: 1.47 * 10^11147096374895 m.
Aphelion midday: 1.52 * 10^11152093625105 m.
Aphelion midnight: 1.52 * 10^11152106374895 m.
Earth's sunward acceleration at perihelion: 6.24 * 10^-30.006237570 m/s^2.
Earth's sunward acceleration at aphelion: 5.64 * 10^-30.005640395 m/s^2.
Surface velocity perihelion midday: 2.98 * 10^429825.13527 m/s.
Sunward acceleration perihelion midday: 6.04 * 10^-30.006047843 m/s^2.
Surface velocity perihelion midnight: 3.08 * 10^430754.86473 m/s.
Sunward acceleration perihelion midnight: 6.45 * 10^-30.006430218 m/s^2.
Surface velocity aphelion midday: 2.88 * 10^428825.13527 m/s.
Sunward acceleration aphelion midday: 5.46 * 10^-30.005463006 m/s^2.
Surface velocity aphelion midnight: 2.98 * 10^429754.86473 m/s.
Sunward acceleration aphelion midnight: 5.84 * 10^-30.005820611 m/s^2.
Differences made: 2.0 * 10^-40.0001897 m/s^2, 2.0 * 10^-40.0001926 m/s^2, 1.8 * 10^-40.0001774 m/s^2 and 2.0 * 10^-40.0001802 m/s^2.
You'd be doing pretty damn well to feel *that*. The largest of those values is only 2.04 * 10^-5 g.only 1.9638*10^-5 g.

Re: Science fleeting thoughts

Posted: Sat May 04, 2019 12:16 pm UTC
by gmalivuk
The differences between the midnight and midday sides are what cause tides, so we'd definitely notice if those were large enough.

However, the difference between perihelion and aphelion doesn't matter nearly as much, because Earth as a whole is also accelerating differently at those times.

The acceleration toward Earth in a spacecraft in LEO is a few thousand times higher than in a spacecraft out near the
Moon, and yet an astronaut in either will feel freefall.

Re: Science fleeting thoughts

Posted: Sat May 04, 2019 9:50 pm UTC
by Sableagle
Part of the tides, at least. I did the same calculations for the Moon's gravity at average distance once, and came up with some vector sums for it all that neatly showed the double-bulge, but I never did the one for the Sun before. I should find those Moon numbers and combine the two effects.
It won't simulate actual observed tides, though, because all those continents get in the way and really complicate things.

Someone in a spaceship 100 m long at 400,000 km or 40,000 km or 4,000 km or 400 km will be in freefall with the spaceship and weightless relative to it, yes, but what if someone was in a spaceship whose bow was at 300 km and whose stern was at 319 km altitude, with enough yaw or pitch rate to keep them that way? I know it sounds insane, but I did get that 19 km figure from starwars.com's page about Super Star Destroyers. With the ship's centre of mass in stable orbit, the bow would be pulled down by stronger gravity and a lower linear velocity at lower radius and the stern would be at super-orbital velocity for its altitude, so the ship would be stretched by its own weight and anyone in the bow or stern would experience some tiny acceleration away from the centre for the same reason. Tiny, but there.

This implies there's a minimum altitude for a Super Star Destroyer about a massive enough planet, below which its hull would be torn apart by its own weight. I don't have the blueprints or the material data sheets, though.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 12:49 am UTC
by ijuin
Given the accelerations exerted upon the SSD by its own propulsion systems, it certainly has enough inertial dampers or whatever to allow it to endure something like a hundred g’s. Tidal accelerations from a normal-density object such as a planet will be much less than that.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 12:02 pm UTC
by gmalivuk
The tidal differential across an object of length L orbiting distance R around an object of mass M is approximately 2GML/R^3

For 20km object in orbit about 300 km above Earth, that's
2*4e14*2e4/3e20, or about a 5.3 cm/s^2 difference.

Given that they've got artificial gravity of apparently 1g or so, a half-percent variation from one end of the ship to the other is probably not a big deal, even ignoring the massive acceleration those ships can clearly handle.

(And the M/R^3 term means that for an orbit just above the surface, tidal forces are proportional to the central body's average density. Earth is the densest thing in our solar system you might orbit a large ship around, everything else poses even less of a problem.)

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 12:15 pm UTC
by gd1
What is the Schwarzsadult radius?

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 1:44 pm UTC
by Eebster the Great
gd1 wrote:What is the Schwarzsadult radius?

The Schwarzschild (pronounced something like Shvarts-sheelt, I think) radius of an object is the hypothetical radius of the event horizon of a nonrotating black hole of that mass. So for instance, if the Sun somehow stopped rotating completely and then imploded, without ejecting any mass in the process, it would form a black hole with a radius of around 3 km. So we say the Sun's Schwarzschild radius is 3 km. The Schwarzschild radius is directly proportional to the mass, so a star with twice the Sun's mass will have twice the Schwarzschild radius. If all of the matter of the star is contained within its Schwarzschild radius, then it's already a black hole.

This comes from Karl Schwarschild, who solved Einstein's field equations for the special case of a spherically-symmetric mass. His solution describes the gravitational field around any body that is the same in all directions, is not rotating, and is not electrically charged. (In practice, big things like stars never have significant charge anyway.) This metric can describe black holes that are spherically symmetric, and this type of black hole is called a Schwarzschild black hole. Schwarzschild black holes are very simple, and they have event horizons that are perfect spheres, so they are often the go-to comparison.

Real black holes are usually rotating, including M87*. This is because most of them form from stars which themselves were rotating before they exhausted their fuel in the core and collapsed. So that rotation doesn't go anywhere; the black hole is still spinning, meaning it is not a Schwarzschild black hole. The faster it is spinning, the more different from a Schwarzschild black hole it becomes. But typically, if you are far enough away from a black hole, it will look pretty similar to a Schwarzschild one anyway, unless it's spinning almost as fast as it can. So the image of M87*, which is pretty blurry anyway, can be understood just fine in terms of the Schwarzschild radius, even though that's not exactly right.

The shadow in the image is not the event horizon of the black hole, which means its radius is not M87*'s Schwarzschild radius. It is actually somewhat larger than that, between 1.5 and 2.6 times the Schwarzschild radius. The details don't seem to be as straightforward as I once thought.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 1:50 pm UTC
by gmalivuk
Yeah but the question was about the SchwarzsADULT radius

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 2:09 pm UTC
by Eebster the Great
Oh this is terribly embarrassing. The Schwarzsadult radius is of course volume over adjusted length squared times half the logarithm of the girth coefficient.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 2:18 pm UTC
by doogly
I think we really just shouldn't talk about the schwarzadult radius on a forum that is only 13+.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 2:21 pm UTC
by Eebster the Great
But as an actual fleeting thought, how does this work in a universe that is contracting or that will eventually contract? In such a universe: (1) if it is homogeneous at a large enough scale, then at a larger enough scale, there will be a mass contained within a sphere of radius much smaller than its Schwarzschild radius, and (2) everything will eventually end up in the same singularity.

These two facts are certainly concordant, but how do we describe such an existence? Particularly in the context of this post? And I get that this isn't actually the Schwarzschild metric, but that doesn't answer the question of what we do with black holes all heading toward the Big Crunch singularity.

Re: Science fleeting thoughts

Posted: Sun May 05, 2019 2:39 pm UTC
by gmalivuk
doogly wrote:I think we really just shouldn't talk about the schwarzadult radius on a forum that is only 13+.

Good point. Further discussion of this topic should be moved to the mature section.

Re: Science fleeting thoughts

Posted: Mon May 06, 2019 2:27 am UTC
by gd1
Alright, but can we at least talk about how Schwarz's child Radius might be taking toys from the other children? I'm not even sure where the toys might be going?

Re: Science fleeting thoughts

Posted: Tue May 07, 2019 8:43 pm UTC
by SuicideJunkie
What if you were to thin out spacetime to the point where incoming waves break, like at the beach?
Would that make an effective shield, causing even particles to break up into quantum foam?

Is that anything like a black hole mulching stuff into hawking radiation?

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 4:27 pm UTC
by Thesh
I recently saw this:

https://en.wikipedia.org/wiki/The_End_o ... %28book%29

Is this just the theory that the universe behaves like Conway's Game of Life where the "experience" of a life-form is independent of the frame rate?

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 5:44 pm UTC
by gmalivuk
Thesh wrote:I recently saw this:

https://en.wikipedia.org/wiki/The_End_o ... %28book%29

Is this just the theory that the universe behaves like Conway's Game of Life where the "experience" of a life-form is independent of the frame rate?

As I recall, no. That still has a clear time dimension even if you slow down the steps, whereas Barbour's idea is that time can be dropped entirely.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 5:45 pm UTC
by Thesh
Okay, then I will happily remain confused.

EDIT: Thinking about this further, Conway's game of life does not have a time component. It has a board with a state, and that state follows rules and changes, and time is purely a result of the sequential nature of the system.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 8:54 pm UTC
by Eebster the Great
Thesh wrote:Okay, then I will happily remain confused.

EDIT: Thinking about this further, Conway's game of life does not have a time component. It has a board with a state, and that state follows rules and changes, and time is purely a result of the sequential nature of the system.

That is the time dimension. In this case, it's discrete, but then so are the spatial dimensions.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 9:09 pm UTC
by Thesh
Is it a dimension, though? You can't go backwards, and forwards doesn't exist until the change occurs. Maybe I'm misunderstanding the concept more than I thought.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 10:19 pm UTC
by Tub
Thesh wrote:Is it a dimension, though?

By any common mathematical definition, time is a dimension. If you want to uniquely identify an event within the universe (or a game of conway), you need 3 (or 2) spatial coordinates and one time coordinate.

Thesh wrote:You can't go backwards, and forwards doesn't exist until the change occurs.

The observed difference between past and future is a consequence of a local entropy gradient; it's (probably) not a fundamental property of a time dimension.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 10:39 pm UTC
by Eebster the Great
There are several closely-related issues coming up here: the arrow of time, the flow of time (A/B-theory), time as a dimension, and time's existence. In Conway's Game of Life, time doesn't flow, but it does have an arrow (the rules are not time-symmetric, so the board evolves different forwards and backwards, unless it is empty), and it is a dimension. In Special Relativity, time still doesn't really flow (it's hard to square the A-theory of time with the relativity of simultaneity), and it does not have an arrow (the laws of physics are time-symmetric), but it is still a dimension. It's unique, in that its signature in the metric is of the opposite sign of the other three dimensions, but it's definitely still a dimension.

Barbour I believe wants a truly timeless theory, with no time dimension at all. I don't really know how this works, but I haven't spent much time reading about it.

Also:

Thesh wrote:Is it a dimension, though? You can't go backwards, and forwards doesn't exist until the change occurs. Maybe I'm misunderstanding the concept more than I thought.


"Before" the change occurs is an earlier state in time. "After" the change occurs is a later state in time.

Re: Science fleeting thoughts

Posted: Wed May 08, 2019 10:49 pm UTC
by Thesh
We can describe things in terms of time, but that doesn't necessarily mean that time actually exists. For example, it may be that everything in the universe can be described in terms of different fundamental dimensions and that dimensions like mass and time can be expressed in terms of units like space, energy, and entropy.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 9:38 am UTC
by Tub
Thesh wrote:We can describe things in terms of time, but that doesn't necessarily mean that time actually exists. For example, it may be that everything in the universe can be described in terms of different fundamental dimensions and that dimensions like mass and time can be expressed in terms of units like space, energy, and entropy.

First of all, time exists. You can observe it. As far as existence proofs go, that's a pretty good one.

The question then becomes: what is time? What you seem to be asking is whether time is a fundamental property or just an emergent phenomena.
Like, in quantum mechanic, the only fundamental things are the wave function and its time dependent evolution. Nowhere does quantum mechanic talk about atoms. According to QM, atoms, molecules and all of chemistry are an emergent thing. That doesn't imply that atoms, the rules of chemistry and consequently you and me don't exist.

Now you might be thinking about a hierarchy of descriptions with increasing level of detail, and the end of the hierarchy will tell us what the fundamental ingredients of our universe are. But that doesn't work out, either. Insights like the holographic principle tell us that you can have equivalent descriptions of the universe with entirely different fundamental ingredients.
Let me quote Tchebu, who explained it way better than I ever could:
Tchebu wrote:Regarding the holographic principle specifically, it is not a model by itself, it's a statement about the theoretical structure of gravity theories. It's the statement that a clever reshuffling of the degrees of freedom in a theory of gravity results in another theory that doesn't explicitly contain gravity and that lives in one dimension lower than the original gravity theory. [...]

This is a specific case of a more general "phenomenon", known as duality. There are many other examples of theories, which look somewhat different if you just list their particle content and interactions, but that can be transformed into each other through a clever reshuffling of their degrees of freedom. It's basically a fancier and more abstract version of changing reference frames in a mechanics problem. Except you're not just changing the position and velocity of some reference point, you're changing what we choose to consider as the fundamental ingredients of the theory. The fact that this is possible indicates that there is no fact of the matter as to what the fundamental ingredients are, just like our ability to change reference frames indicates that there's no fact of the matter as to who is moving and who is at rest. I don't think the significance of such conceptual achievements can be overstated and I'm semi-expecting philosophers to make a big deal of this at some point in the future.

So yes, it's entirely plausible that we can create a description of our universe that doesn't include time as a fundamental ingredient, but such a theory must contain something that we'd recognize as time as an emergent feature. Because time exists, and no description of our universe is complete without it.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 1:17 pm UTC
by doogly
Tub wrote:Like, in quantum mechanic, the only fundamental things are the wave function and its time dependent evolution. Nowhere does quantum mechanic talk about atoms.

Wave functions are waaaaaack, algebra of operators 4lyfe.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 2:31 pm UTC
by Thesh
What I'm trying to understand is what they are talking about by asking for a timeless physics. I thought his description sounded like Conway's Game of Life, which is what I'm asking. My point is that the entirety of the state of Conway's Game of Life is the position of the cells, and an evolution function which does not include time in the description, but only tells you the next position. The consequence of applying that to the universe is that you can describe the universe as position and energy, and use a evolution function to describe the movement of particles. Relativity would not be needed to explain what we describe as time dilation - imagine a box with a ball bouncing in it, that ball moves at a constant speed, but also moves with the box; as you move the box, the bouncing appears to slow, stopping when the box and ball are traveling at the same speed, but the speed of the ball itself never changes.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 3:09 pm UTC
by Eebster the Great
I'm not understanding the difference between the argument of an evolution function and the dimension of time.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 3:33 pm UTC
by Thesh
There would be no four-dimensional space-time, just three-dimensional space; the speed could be infinite, but we would experience the same thing simply because you must go from A to B before you can go from B to C.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 3:38 pm UTC
by Eebster the Great
It's not like time isn't a dimension in classical physics. But I'm also not understanding how you can reproduce the invariance of the speed of light in your model.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 3:52 pm UTC
by Thesh
The relative speed of light would be variant, but the local systems would evolve at a different rate and light would appear to be invariant.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 4:04 pm UTC
by Eebster the Great
. . . but how? You say that it would, but I don't get how this works at all.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 4:15 pm UTC
by Thesh
I don't get how it works either, I'm just trying to understand how it could, lol. The bouncing ball in a box is how I'm visualizing it; because the ball must move to an adjacent position each frame (all particles move at the same speed), the rate at which it bounces inside the box (the clock) changes relative to the speed of the box.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 4:39 pm UTC
by Tub
Thesh wrote:My point is that the entirety of the state of Conway's Game of Life is the position of the cells, and an evolution function which does not include time in the description, but only tells you the next position.

Considering that time is discrete here, your evolution function implicitly works on a time interval of length 1. Given such a function, I can trivially construct an evolution function that takes an arbitrary time t and evolves the universe accordingly. You did not get rid of time, you merely hid it.

I'm not sure what you're trying to tell us about relativity. For example, relativity tells us that, for some pairs of events, it is impossible for any observer to tell which event happened first. If you want to model the universe as a single state that evolves with time, you will find that you must now have a global definition of which events happened in the same state and which didn't, thus you can also tell which event happened first. In an attempt to get rid of time, you made unobservable predictions. That's not an improvement.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 4:46 pm UTC
by Thesh
Tub wrote:
Thesh wrote:My point is that the entirety of the state of Conway's Game of Life is the position of the cells, and an evolution function which does not include time in the description, but only tells you the next position.

Considering that time is discrete here, your evolution function implicitly works on a time interval of length 1. Given such a function, I can trivially construct an evolution function that takes an arbitrary time t and evolves the universe accordingly. You did not get rid of time, you merely hid it.


Are you arguing against me, or him? I'm trying to understand what he's saying, not trying to tell you what is correct.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 5:06 pm UTC
by gmalivuk
I mean, the book is still in print as far as I know, you can just read it instead of speculating about what arguments you think it might make.

Re: Science fleeting thoughts

Posted: Thu May 09, 2019 5:15 pm UTC
by Thesh
I'm just curious as to what he means; if I'm correct, then I don't really have a reason to read it. I've already got enough books that I'm not reading, anyway.

EDIT: I watched a lecture, but in the middle of it he said "My conjecture is that not only does time not exist, but at a fundamental level distance does not exist"

Yeah, fuck this. I'm out of here.