Science fleeting thoughts

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Re: Science fleeting thoughts

Postby gmalivuk » Tue Jul 09, 2019 8:43 pm UTC

Quizatzhaderac wrote:
Eebster the Great wrote:No, the energy levels are quantized. The electron can't ever be excited by metric expansion unless it's happening dozens of orders of magnitude faster than it is now.
What are you suggesting is the time limit for this effect to occur?

What effect should have a time limit?

Nearby galaxies remain gravitationally bound from millions of light years away. The hugely increased strength of EM forces together with the hugely decreased distances within an atom suggest that time isn't the issue, but rather the Hubble parameter is far, far too small.

It's not the case that the observable universe necessarily shrinks in an expanding universe. It can eternally expand itself.
As it expands, parts of it become unobservable to other parts; the faster the expansion, the smaller any observer's observable universe. An observable universe of constant expansions has a radius inversely proportional to it's Hubble constant.
Okay, so that means it couldn't shrink unless the Hubble parameter is increasing. Which it couldn't be without phantom energy.
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Re: Science fleeting thoughts

Postby Pfhorrest » Tue Jul 09, 2019 9:05 pm UTC

Tangentially related question (tangential to the current topic of conversation):

Suppose there were a civilization of hyperintelligent microorganisms living on the surface of a slowly inflating balloon. I presume they could in principle build something to extract energy from the expansion of the balloon, as the things they live on and among on the surface of the balloon slowly move away from each other. What would such a device look like?
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Re: Science fleeting thoughts

Postby Quizatzhaderac » Tue Jul 09, 2019 9:35 pm UTC

gmalivuk wrote:What effect should have a time limit?

Nearby galaxies remain gravitationally bound from millions of light years away. The hugely increased strength of EM forces together with the hugely decreased distances within an atom suggest that time isn't the issue, but rather the Hubble parameter is far, far too small.
I posited a small effect, Eebster responded with "No... can't ever", so I took that to mean he was saying excitation of electrons was non-existent, not merely small.

As for the "time limit". Eebster mentioned quantization for why a supposedly small effect would become zero, hence rounding down. Hubble's constant is in units of frequency, meaning any excitation would a certain period, a longer period for EM bound states, and shorter period for gravitationally bound states

Okay, so that means it couldn't shrink unless the Hubble parameter is increasing. Which it couldn't be without phantom energy.
The context was on the same page you were quoting from, a mere two posts back was all you needed to read to understand.
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Re: Science fleeting thoughts

Postby gmalivuk » Wed Jul 10, 2019 12:39 am UTC

Quizatzhaderac wrote:
gmalivuk wrote:What effect should have a time limit?

Nearby galaxies remain gravitationally bound from millions of light years away. The hugely increased strength of EM forces together with the hugely decreased distances within an atom suggest that time isn't the issue, but rather the Hubble parameter is far, far too small.
I posited a small effect, Eebster responded with "No... can't ever", so I took that to mean he was saying excitation of electrons was non-existent, not merely small.
He said "can't ever...unless it's happening dozens of orders of magnitude faster than it is now."

As for the "time limit". Eebster mentioned quantization for why a supposedly small effect would become zero, hence rounding down. Hubble's constant is in units of frequency, meaning any excitation would a certain period, a longer period for EM bound states, and shorter period for gravitationally bound states
The fact that something has the same units as frequency doesn't mean it is a frequency of any kind.

Okay, so that means it couldn't shrink unless the Hubble parameter is increasing. Which it couldn't be without phantom energy.
The context was on the same page you were quoting from, a mere two posts back was all you needed to read to understand.

You were responding to Eebster's statement that "it's not the case that the observable universe necessarily shrinks in an expanding universe". Do you agree with that statement? If so, why were you responding as though clarifying something Eebster wasn't understanding about your idea?

In any case, the current model predicts that the Hubble parameter will decrease forever, asymptotically approaching 57 km/s/Mpc.
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Re: Science fleeting thoughts

Postby Eebster the Great » Wed Jul 10, 2019 1:26 am UTC

I have an unrelated fleeting thought. This paper rejects a model (in which what scientists believe to be cosmological redshift is actually relativistic redshift) to a confidence level of 23 σ. This paper reports GZK suppression of ultra-high energy cosmic rays to over 20 σ. In 2007, Goldman Sachs reportedly had models so embarrassingly wrong, they were getting 25 σ events "several days in a row."

What is the highest confidence you have ever seen reported in terms of standard deviations from the mean?

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Re: Science fleeting thoughts

Postby Quizatzhaderac » Wed Jul 10, 2019 5:43 pm UTC

@gmalivuk MY comment about reading the context towards you was peevish and uncalled for, and I apologize.
gmalivuk wrote:He said "can't ever...unless it's happening dozens of orders of magnitude faster than it is now."
Yes, electron can't even become exited by universal expansion unless universal happening dozens of orders of magnitude faster than it is now. Not "electrons are exited in proportion to universal expansion, which is very small." which is what I suggested in the first place.
You were responding to Eebster's statement that "it's not the case that the observable universe necessarily shrinks in an expanding universe". Do you agree with that statement? If so, why were you responding as though clarifying something Eebster wasn't understanding about your idea?
Yes, I do. Conversation in spoilers.
Spoiler:
Eebster the Great wrote:If we put the universe in a box of constant volume, it's inevitable that a given state would eventually recur, thus putting the universe in an infinite loop. But for an infinitely expanding universe, that needn't happen.
Ebester in contrasting the cases of a universe in a box "of constant volume" and an infinitely expanding one.

He was also making reference to the a finite sized universe has a finite number of configurations, and likely implying that an infinitely expanding universe does not have a finite number of configurations.
Quizatzhaderac wrote:An expanding universe would have a horizon, and thus a limited "visible universe" within. The greater the expansion, the smaller the visible universe and the fewer possible states. So in a sense, an expanding universe is necessarily finite.
I argued that an expanding universe (in a sense) has a finite number of configurations. I did not specify if the universe was expanding constantly, accelerating, or whatever. (All that is required is that expansion in positive on average.)
Eebster the Great wrote:It's not the case that the observable universe necessarily shrinks in an expanding universe. It can eternally expand itself.
Which is true. But I apparently gave Eebster the impression that I was talking about a single universe with a changing horizon distance.
Quizatzhaderac wrote:As it expands, parts of it become unobservable to other parts; the faster the expansion, the smaller any observer's observable universe. An observable universe of constant expansions has a radius inversely proportional to it's Hubble constant.

The contents of the box are eternally expanding, but they contents become casually disconnected from each other, so in an important sense, they stop being in the same universe.
I was reiterating my point from my previous post, (IMHO) more clearly. This did not directly contract Eebster's previous statement. I assumed Eebster though his statement was contradicting mine, which meant I needed to clarify.
The fact that something has the same units as frequency doesn't mean it is a frequency of any kind.
True, I need to show more work to prove that. The Hubble parameter is properly in units of kilometers per second per megaparsec, which cancels out to units of frequency.

When we look at two points and call the current distance between them x an some larger distance y. Using the Hubble parameter (in the most straight forward possible manner) we can assign a speed the the two points are moving away from each other at distance X, distance y, and every distance between. If we integrate the multiplicative inverse of this speed from x to y we get the period of time it takes for x to turn into y.

Quantum states are (in part) defined by the distance between two particles, so by changing nothing but distances, one can change states. Looking at two states (differentiated only by having different distances) we can describe the time period it would take inflation to turn the closer state into the further state.

Now, I admit there's till plenty of room to say that maybe we can't apply inflation to quantum system like this, or how it should be applied. But a naive interpretation of inflation does produce exactly the units for a certain period to correspond to the change in quantum states.

The interpretation I'm favoring right now, is that the probability density of tan electron in an s1 oribital is constantly drifting outward very slowly (slowly enough to be dwarfed by quantum uncertainty, and probably a host of other factors). Natural resonances cause the probability to become a superposition of s1 and s2 orbitals. The strong EM force causes the s2 orbital to decay so quickly that it's next to impossible to observe an electron in a s2 orbital before it emits a photon.
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Re: Science fleeting thoughts

Postby gmalivuk » Wed Jul 10, 2019 8:42 pm UTC

Quizatzhaderac wrote:
Quizatzhaderac wrote:An expanding universe would have a horizon, and thus a limited "visible universe" within. The greater the expansion, the smaller the visible universe and the fewer possible states. So in a sense, an expanding universe is necessarily finite.
I argued that an expanding universe (in a sense) has a finite number of configurations. I did not specify if the universe was expanding constantly, accelerating, or whatever. (All that is required is that expansion in positive on average.)

This is false, even if we accept that "finite observable universe" is (in a relevant sense) the same as "finite universe", which I don't, and even if we also assume that a finite universe really does mean a finite number of states, as though on some level everything is integers.

Let's take the really simplified example of a 2D grid universe following some cellular automaton rules akin to Conway's Life.
1) Obviously if it stays at a constant finite size, there are only finitely many possible states, and thus only finitely many future states. (And if the rules are memoryless and deterministic and static, repeating a particular state will guarantee a loop.)
2) If it shrinks, then the number of possible states throughout the future is even more limited (though repetition would only be guaranteed once it reaches a minimum size and then stops shrinking).
3) If it expands, then though there are only finitely many possible states at a given time, there are infinitely many possible future states because the finite number of possible-states-now keeps increasing. (All integers are finite but there are still infinitely many of them.)

The observable universe can only shrink if the Hubble parameter increases over time, which requires a kind of matter we have no evidence of.
The observable universe stays the same size if the Hubble parameter stays the same size over time, which is indeed the long-term future prediction of our universe but which is at one extreme of the possible things a universe can do.
The observable universe expands if the Hubble parameter decreases over time, which seems to be what it's doing now and which is also what it would do in a linearly expanding universe or a decelerating expanding universe.

If the whole universe is infinite and if the deceleration parameter is bounded above -1 (i.e. if it might decrease over time but can never get closer than some epsilon to -1), then the Hubble parameter decreases asymptotically toward 0 and the observable universe grows without bound.
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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Jul 11, 2019 2:14 am UTC

Quizatzhaderac wrote:Quantum states are (in part) defined by the distance between two particles, so by changing nothing but distances, one can change states. Looking at two states (differentiated only by having different distances) we can describe the time period it would take inflation to turn the closer state into the further state.

I'm not understanding how this is supposed to happen. If I am pushed upward by a pressure of 1 pPa, I won't fly off the Earth, ever. I will have slightly more energy, but not enough to be excited to a higher energy level. The ground state will just be marginally higher.

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Re: Science fleeting thoughts

Postby Sizik » Thu Jul 11, 2019 12:18 pm UTC

Pfhorrest wrote:Tangentially related question (tangential to the current topic of conversation):

Suppose there were a civilization of hyperintelligent microorganisms living on the surface of a slowly inflating balloon. I presume they could in principle build something to extract energy from the expansion of the balloon, as the things they live on and among on the surface of the balloon slowly move away from each other. What would such a device look like?


Either something anchored to the surface of the balloon at two points so that work can be derived from the increasing distance between them, or something encircling the balloon so that work can be derived from the balloon expanding within it.
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Re: Science fleeting thoughts

Postby p1t1o » Thu Jul 11, 2019 2:21 pm UTC

Sizik wrote:
Pfhorrest wrote:Tangentially related question (tangential to the current topic of conversation):

Suppose there were a civilization of hyperintelligent microorganisms living on the surface of a slowly inflating balloon. I presume they could in principle build something to extract energy from the expansion of the balloon, as the things they live on and among on the surface of the balloon slowly move away from each other. What would such a device look like?


Either something anchored to the surface of the balloon at two points so that work can be derived from the increasing distance between them, or something encircling the balloon so that work can be derived from the balloon expanding within it.


If you extrapolate that to us living in our universe, we'd have to build a machine with extra-dimensional components, that is capable of gripping space. And Im not sure if that is plausible.

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Re: Science fleeting thoughts

Postby pogrmman » Thu Jul 11, 2019 3:01 pm UTC

I don’t know if this is the right thread for this, but I thought this radar loop from last night was pretty cool.
B631EC08-F247-4C01-B318-379D12B86B9E.gif


So, all those blue-green circles are emergences of Mexican free tailed bats from caves, tunnels, and bridges all over central TX. The largest colony in the world is just north of San Antonio, but the bats are hard to see because it’s close to the radar site. There’s a thunderstorm complex and associated outflow front moving south at 40-50 mph.

What surprised me is that it looks like the outflow boundary is actually blowing the bats south with it! I’d never thought about what happens to them when it gets really windy, but it would make sense that that’s what’s happening: 40-50 mph wind could certainly push around such a little flying critter.

I’m wondering if that’s actually what happened or if it’s some trick of the radar (or if the bats flew away from the wind as it came).

EDIT: Apologies if the gif seems shaky: it’s not on my device, but it looks wonky to me when I view the uploaded file...

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Re: Science fleeting thoughts

Postby p1t1o » Thu Jul 11, 2019 3:45 pm UTC

Thats really cool!

I presume the bats are conciously fleeing the weather, if they were just at the mercy of the wind it wouldnt be much fun.

What is the timescale? Im wondering if there might be second-order effects, like the storm pushes insects and the bats chase those, so it looks like the storm is pushing the bats, but that would take time to show like this on a scope, Im guessing.

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Re: Science fleeting thoughts

Postby Pfhorrest » Thu Jul 11, 2019 4:17 pm UTC

p1t1o wrote:
Sizik wrote:
Pfhorrest wrote:Tangentially related question (tangential to the current topic of conversation):

Suppose there were a civilization of hyperintelligent microorganisms living on the surface of a slowly inflating balloon. I presume they could in principle build something to extract energy from the expansion of the balloon, as the things they live on and among on the surface of the balloon slowly move away from each other. What would such a device look like?


Either something anchored to the surface of the balloon at two points so that work can be derived from the increasing distance between them, or something encircling the balloon so that work can be derived from the balloon expanding within it.


If you extrapolate that to us living in our universe, we'd have to build a machine with extra-dimensional components, that is capable of gripping space. And Im not sure if that is plausible.

Would not the two end of the first device be pulled apart from one another even if they were simply sitting unattached on the surface of the balloon? No extradimension tethering required, just inertia plus expanding space gets you two things moving apart from each other, and you can use that to perform work, no?
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Re: Science fleeting thoughts

Postby pogrmman » Thu Jul 11, 2019 4:19 pm UTC

p1t1o wrote:Thats really cool!

I presume the bats are conciously fleeing the weather, if they were just at the mercy of the wind it wouldnt be much fun.

What is the timescale? Im wondering if there might be second-order effects, like the storm pushes insects and the bats chase those, so it looks like the storm is pushing the bats, but that would take time to show like this on a scope, Im guessing.

It was in precipitation mode at the time, so the frames are about 5 minutes apart. The loop has 15 frames, so that’s about an hour and 15 minutes. The wind was pretty strong: there were lots of reported gusts in the 40-50 mph range on the ground, so I imagine even stronger higher up.

I don’t know enough about bats to say exactly what happened beyond the radar observation. I don’t know how fast bats can fly, but the boundary was moving at 40 mph: that seems pretty fast to try and escape!

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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Jul 11, 2019 4:24 pm UTC

p1t1o wrote:
Sizik wrote:
Pfhorrest wrote:Tangentially related question (tangential to the current topic of conversation):

Suppose there were a civilization of hyperintelligent microorganisms living on the surface of a slowly inflating balloon. I presume they could in principle build something to extract energy from the expansion of the balloon, as the things they live on and among on the surface of the balloon slowly move away from each other. What would such a device look like?


Either something anchored to the surface of the balloon at two points so that work can be derived from the increasing distance between them, or something encircling the balloon so that work can be derived from the balloon expanding within it.


If you extrapolate that to us living in our universe, we'd have to build a machine with extra-dimensional components, that is capable of gripping space. And Im not sure if that is plausible.

It's the scale that makes it implausible, not the mechanics. If you have an object in the Local Group and an object in the Virgo Cluster, and they are both exerting a force on each other, then as they recede due to Hubble Flow, that force will do work, and in principle, it could generate usable energy. The problem is that any force between two objects 60 million light years apart is negligible.

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Re: Science fleeting thoughts

Postby gmalivuk » Thu Jul 11, 2019 4:43 pm UTC

Nah, just tie a rope between them and profit as it winds out at 1260km/s!
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Re: Science fleeting thoughts

Postby Pfhorrest » Thu Jul 11, 2019 4:48 pm UTC

Yeah I'm talking about like, if you have a Kardeshev Type IV civilization that might build structures spanning the size of the observable universe.
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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Jul 11, 2019 4:58 pm UTC

Pfhorrest wrote:Yeah I'm talking about like, if you have a Kardeshev Type IV civilization that might build structures spanning the size of the observable universe.

You know the rope would just snap, right? As would any other conceivable physical structure of even the most minuscule fraction of that scale.

Surprisingly though, its mass would be smaller than the Earth's. It's hard to get a sense of scale for these sorts of things.

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Re: Science fleeting thoughts

Postby Sizik » Thu Jul 11, 2019 5:05 pm UTC

Pfhorrest wrote:Would not the two end of the first device be pulled apart from one another even if they were simply sitting unattached on the surface of the balloon? No extradimension tethering required, just inertia plus expanding space gets you two things moving apart from each other, and you can use that to perform work, no?


It depends on the relative strengths of the force needed to pull the ends apart, and the force (e.g. friction) that keeps the ends in one place on the balloon. If the first is greater than the second, then it will just sit "in place" while the balloon expands beneath.

Hence the second option, which isn't reliant on space moving the device itself, but requires the fact that the balloon surface loops back on itself.
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Re: Science fleeting thoughts

Postby gmalivuk » Thu Jul 11, 2019 5:15 pm UTC

Eebster the Great wrote:
Pfhorrest wrote:Yeah I'm talking about like, if you have a Kardeshev Type IV civilization that might build structures spanning the size of the observable universe.

You know the rope would just snap, right?

I mean, yeah, I didn't intend for anyone to assume I was actually talking about a rope.

The point is that metric expansion could in principle do work.
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Re: Science fleeting thoughts

Postby Eebster the Great » Thu Jul 11, 2019 6:49 pm UTC

gmalivuk wrote:
Eebster the Great wrote:
Pfhorrest wrote:Yeah I'm talking about like, if you have a Kardeshev Type IV civilization that might build structures spanning the size of the observable universe.

You know the rope would just snap, right?

I mean, yeah, I didn't intend for anyone to assume I was actually talking about a rope.

The point is that metric expansion could in principle do work.

I'm quoting pfhorrest because my point is that any structure spanning a supercluster is not going to hold together.

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Re: Science fleeting thoughts

Postby Sableagle » Thu Jul 11, 2019 8:53 pm UTC

Even if it could stand up to *being*, wouldn't a structure spanning a supercluster have a serious problem with impacts? Parts of it would have to be within galaxies, wouldn't they?
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Re: Science fleeting thoughts

Postby Pfhorrest » Thu Jul 11, 2019 9:25 pm UTC

The kind of civilization I imagine would bother with building such a thing would be the kind of civilization that had already disassembled all the galaxies. Capture all the escaping starlight with Dyson spheres, use that to starlift all the stars so they stop burning perfectly good fuel and building materials until you need them, and then use a bunch of that disassembled starstuff to build something on the scale of the observable universe to somehow capture the energy of the metric expansion of space so that your civilization doesn't die a heat death.

I'm envisioning loosely something like a Dyson sphere encircling the observable universe, its constituent pieces somehow or another holding on to each other (strategically placed dark matter?) against the metric expansion of space, and generating power from the flow of energy coming from the hollow center of the thing full of empty space constantly filling with dark energy, that flows past the structure out into the void beyond the observable universe.

(For the balloon microorganism analogy: imagine they build a large circle on the surface of their balloon, with radially-oriented wheels on the bottom of the structure. As the balloon expands, and the circle stays the same size against that expansion, the wheels under it turn, which can be used to do work. I'm not clear on exactly what the universe-scale analog of that would be, which is why I brought it up).

You can keep planets around where you like them, illuminated by slow-burning dwarf stars (appropriately closer than a larger stars would be, as needed), fed a controlled stream of hydrogen to burn as long as you like, hydrogen that you can now produce yourself (albeit at a limited rate) from the free energy you've now tapped into. But by that point you get to choose where those little massive bodies like stars and planets go, so you don't have to worry about them running into your universe-spanning superstructure.

ETA: thinking about the big-picture numbers some more, there's about three times more dark energy than everything else (most of the rest dark matter) in the universe, so I guess the very best you could possibly do at the start is to build a structure that captures less than 1/3 of the available dark energy, because something bigger than that would be blown apart by the dark energy it's trying to contain (assuming here that it's primarily gravity holding the thing together, and naively assuming that the gravitational attraction of the dark [and ordinary] matter is proportional to its energy content in a way that's inversely proportional to an equivalent amount of dark energy pushing things apart, which for all I know might be completely wrong to assume). But once you've got that built, you have access to a continuous source of energy that dwarfs what you'd get from the antimatter annihilation of all the normal matter in the universe, and you can use that energy to build more ordinary matter (pull quarks apart from each other to make more quarks, etc), and you can use that matter to make your structure bigger and bigger to capture more and more energy up to the limit imposed by the Hubble constant, where the opposite ends of your structure would be getting accelerated away from each other faster than light. And on the smaller end of things, you wouldn't have to start with building the biggest, most universe-encircling structure you could build with the available matter already in the universe; you could move in steps, from the Dyson spheres we started with, to a galaxy-scale equivalent thereof (made of the starlifted matter from that galaxy, encircling its central supermassive black hole, maybe stealing rotational energy from that supermassive black hole as an intermediary power source, and eventually harvesting its Hawking radiation), then on to cluster and supercluster scale equivalents thereof, before getting on to building the universe-scale final solution.
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Jul 12, 2019 3:23 am UTC

Pfhorrest wrote:I'm envisioning loosely something like a Dyson sphere encircling the observable universe, its constituent pieces somehow or another holding on to each other (strategically placed dark matter?) against the metric expansion of space, and generating power from the flow of energy coming from the hollow center of the thing full of empty space constantly filling with dark energy, that flows past the structure out into the void beyond the observable universe.

The structures need to actually move away from each other to do work.

(For the balloon microorganism analogy: imagine they build a large circle on the surface of their balloon, with radially-oriented wheels on the bottom of the structure. As the balloon expands, and the circle stays the same size against that expansion, the wheels under it turn, which can be used to do work. I'm not clear on exactly what the universe-scale analog of that would be, which is why I brought it up).

Can you explain this more or draw a picture. I'm having a difficult time visualizing it. What makes the wheels turn?

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Re: Science fleeting thoughts

Postby ucim » Fri Jul 12, 2019 3:36 am UTC

Eebster the Great wrote:Can you explain this more or draw a picture. I'm having a difficult time visualizing it. What makes the wheels turn?
I think he means, imagine little bicycles on the outside of the balloon, rolling on its surface (ignoring the fact that the "universe" is the surface). Each bicycle is two wheels held together by a frame. Remembering the airplane on a treadmill, this is a treadmill that is expanding, so it's moving in opposite directions for each wheel. At least one of the wheels has to turn.

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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Jul 12, 2019 4:11 am UTC

Oh, I was imagining wheels on the surface of the balloon rather than perpendicular to it. Now I get the whole extradimensional gripping spacetime thing.

For this to work, some available dimensions must be expanding more than others, but also idk how friction is gonna work here. Maybe if the universe were a 3-brane expanding in a larger bulk or something this could work, but submillimeter gravitational experiments seem to rule this out down to extra dimensions at most ~50 microns in radius.

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Re: Science fleeting thoughts

Postby Pfhorrest » Fri Jul 12, 2019 4:30 am UTC

Can you explain why some dimensions have to be expanding more than others? The circle on an expanding balloon is meant to be an easier-to-visualize analog of a three-dimensional sphere in an expanding space. Like, ignoring all physical forces for the moment and just considering geometry, if you have a spherical arrangement of point-like objects in a three-dimensional space, and that space expands, in all dimensions uniformly, those point-like objects are going to move apart from each other. If you then somehow attach them all to each other, then a tension will be applied across all of the connections; I'm not sure if there's any way of extracting useful energy from that, though I'd like to hear a more considered answer on that front. Regardless of that, if we then imagine that that three-dimensional space is filled with a bunch of other bits of stuff, like a gas, then as that space expands that stuff in the middle is going to be flowing past the spherical arrangement of connected bits, continuously, and that's definitely something that can be used to generate useful work. Since no space is actually completely empty, and as I understand it dark energy is basically adding very small amounts of new energy everywhere, even if your entire universe just consisted of this spherical bubble in an otherwise "empty" expanding space, there would still be some flow of energy from inside the spherical bubble to the outside of it. I don't know the specifics of how that could be harnessed, and it would of course be a ridiculously weak flow across any particular human-scale part of the spherical structure, but if you somehow worked out exactly how to harness that ridiculously weak flow of energy for the tiny little bit that it's worth, and you did that around the perimeter of the entire observable universe, you'd have a collectively huge energy source at your disposal.
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Jul 12, 2019 5:30 am UTC

Pfhorrest wrote:Can you explain why some dimensions have to be expanding more than others? The circle on an expanding balloon is meant to be an easier-to-visualize analog of a three-dimensional sphere in an expanding space.

Well, it's a two-dimensional sphere, but I know it's an analogy. My point was that in order for wheels to be at right angles to the surface, there needs to be an extra dimension for them to inhabit. And if that dimension were expanding just as much as the other two, the wheel would simply be pulled away from the surface of the balloon. There needs to be something like a D-brane holding the wheel to the plane.

Like, ignoring all physical forces for the moment and just considering geometry, if you have a spherical arrangement of point-like objects in a three-dimensional space, and that space expands, in all dimensions uniformly, those point-like objects are going to move apart from each other. If you then somehow attach them all to each other, then a tension will be applied across all of the connections; I'm not sure if there's any way of extracting useful energy from that, though I'd like to hear a more considered answer on that front.

As gmalivuk said, this does work. You can imagine attaching the ropes to turbines, spinning them as they unwind. This can of course be used to generate useful electrical currents. That's what I was talking about when I said it's a problem of scale.

Regardless of that, if we then imagine that that three-dimensional space is filled with a bunch of other bits of stuff, like a gas, then as that space expands that stuff in the middle is going to be flowing past the spherical arrangement of connected bits, continuously, and that's definitely something that can be used to generate useful work. Since no space is actually completely empty, and as I understand it dark energy is basically adding very small amounts of new energy everywhere, even if your entire universe just consisted of this spherical bubble in an otherwise "empty" expanding space, there would still be some flow of energy from inside the spherical bubble to the outside of it. I don't know the specifics of how that could be harnessed, and it would of course be a ridiculously weak flow across any particular human-scale part of the spherical structure, but if you somehow worked out exactly how to harness that ridiculously weak flow of energy for the tiny little bit that it's worth, and you did that around the perimeter of the entire observable universe, you'd have a collectively huge energy source at your disposal.

If you want the ends of your sphere not to recede from each other, they actually have to move toward each other at nearly the speed of light. You could get energy from these things whizzing through and past galaxies by collecting the high-energy gas and dust that flies past, but doing so will cost momentum, slowing you down. There is no free lunch. Worse, eventually the galaxy clusters will have moved far away and there will be nothing left in the middle of your collectors.

And dark energy is energy, but that doesn't mean it produces other kinds of energy. The total energy content of the universe is increasing because there is more space expanding, not because there is an increasing amount of matter in it.

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Re: Science fleeting thoughts

Postby Pfhorrest » Fri Jul 12, 2019 6:20 am UTC

Eebster the Great wrote:My point was that in order for wheels to be at right angles to the surface, there needs to be an extra dimension for them to inhabit. And if that dimension were expanding just as much as the other two, the wheel would simply be pulled away from the surface of the balloon. There needs to be something like a D-brane holding the wheel to the plane.

Okay, I didn't mean that part of the analogy to be so literal; I wasn't picturing there's be hypercylindrical 4D wheels rolling against the hypersurface of 3D space, but rather something more like regular 3D turbines in the 3D space, but I'm not sure what the 2D equivalent of a turbine in a 2D space would be, or if there even is such a thing.

And dark energy is energy, but that doesn't mean it produces other kinds of energy. The total energy content of the universe is increasing because there is more space expanding, not because there is an increasing amount of matter in it.

Energy is energy. If you have an empty space that is expanding, and you abstractly demarcate a fixed volume in that space that does not expand with it, is there not a constant and (so long as the expansion continues) unending flow of energy from within that volume to outside that volume? The energy won't be very dense, being just the vacuum energy, but it will be something, and a very low-density something across an enormous volume is still a lot of that thing. So if you have some structure holding itself together against that expansion of space -- and we know that some such structures can exist, like galaxies, whose internal gravitational binding is stronger than the expansion of space -- then there will be a constant low-density flow of energy from inside the structure to the universe beyond it. If that structure is then hollow, acting as a membrane between the interior and exterior of it, then you have a flow of energy across that barrier, that could in principle do useful work.

Imagine for illustration if the expansion of space was much much higher, but still not so high as to overcome the electromagnetic forces that hold ordinary matter together. If you then had a large sphere of ordinary matter, held together by those ordinary electromagnetic forces, would there not be some kind of pressure difference between the inside of the sphere and the outside of it, that could be put to use doing some kind of work? If so, then to do the same with the slower expansion of space we have now, you just need to enclose a much much bigger volume, with a structure necessarily held together by much stronger forces, comparable to the gravitational forces that hold galaxies together against the expansion of space.
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Re: Science fleeting thoughts

Postby gmalivuk » Fri Jul 12, 2019 11:49 am UTC

Galaxies hold themselves together with gravity, which means everything inside them is also held together and there's no flow of energy caused by metric expansion.

To build something that has distant, non-gravitationally-bound pieces that aren't moving away from each other, you'd have to accelerate them all towards the common center. The stuff flowing out of the sphere would, to each part of the sphere, just look like plain old drag. I'm not sure how that would give you more energy than you put into it.
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Jul 12, 2019 12:00 pm UTC

Pfhorrest wrote:Imagine for illustration if the expansion of space was much much higher, but still not so high as to overcome the electromagnetic forces that hold ordinary matter together. If you then had a large sphere of ordinary matter, held together by those ordinary electromagnetic forces, would there not be some kind of pressure difference between the inside of the sphere and the outside of it, that could be put to use doing some kind of work? If so, then to do the same with the slower expansion of space we have now, you just need to enclose a much much bigger volume, with a structure necessarily held together by much stronger forces, comparable to the gravitational forces that hold galaxies together against the expansion of space.

There is no pressure gradient to exploit. The negative pressure is the same everywhere. Aside from that, to do work, something needs to move. If everything is stationary, work is zero.

Like, if I put a rope in tension, and I'm just holding it still, I'm not getting any energy out of it. But if I put a rope in tension and pull something with it, that movement can be used. The rope is doing work, which is force times distance.

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Re: Science fleeting thoughts

Postby p1t1o » Fri Jul 12, 2019 12:21 pm UTC

gmalivuk wrote:
Eebster the Great wrote:
Pfhorrest wrote:Yeah I'm talking about like, if you have a Kardeshev Type IV civilization that might build structures spanning the size of the observable universe.

You know the rope would just snap, right?

I mean, yeah, I didn't intend for anyone to assume I was actually talking about a rope.

The point is that metric expansion could in principle do work.


Where is the work coming from? Is the expansion of space slowed locally? There must be an effect of some kind, right?

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Re: Science fleeting thoughts

Postby cyanyoshi » Fri Jul 12, 2019 2:01 pm UTC

As I understand it, two objects in expanding space naturally move apart exponentially. Then you should be able to collect energy by lassoing an object a billion light-years away and gather the heat from friction as the rope slips through your hands....I think.

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Re: Science fleeting thoughts

Postby p1t1o » Fri Jul 12, 2019 2:04 pm UTC

cyanyoshi wrote:As I understand it, two objects in expanding space naturally move apart exponentially. Then you should be able to collect energy by lassoing an object a billion light-years away and gather the heat from friction as the rope slips through your hands....I think.


But the Joules of energy now in your hand, where are they taken from? Someplace must lose Joules, no?

Im aware of this: http://www.preposterousuniverse.com/blo ... conserved/

But something must change somewhere.

If I imagine this rope, it is keeping the distance (unless the concept of "distance" is changing?) constant, but the rest of the universe is moving apart around it, pulling on the objects at either end and creating tension in the rope. So in effect, you now have two object moving appearing to accelerate towards each other...but now Im stuck because of the constant distance delineated by the rope...???

But you could allow this rope to "slip" as you say, and extract work. But again im stuck as to where this work is drained from.

Are not the atoms in the rope also pulled further apart, lengthening the rope at the same rate as universal expansion? But this would remove tension and any ability to extract work...

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Re: Science fleeting thoughts

Postby elasto » Fri Jul 12, 2019 2:29 pm UTC

p1t1o wrote:But you could allow this rope to "slip" as you say, and extract work. But again im stuck as to where this work is drained from.

My thoughts:

As the space between things expands, their gravitational potential energy increases.

So by applying friction to the rope, you slow down the rate at which the distant object moves away from you, stealing from this increasing potential energy and converting it to heat?

(Or is that too 'Newtonian' a picture of what's happening here...)

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Re: Science fleeting thoughts

Postby gmalivuk » Fri Jul 12, 2019 2:43 pm UTC

I guess in a sense it's slowing the expansion somewhat in the limited region occupied by the ends of the rope.
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Re: Science fleeting thoughts

Postby Eebster the Great » Fri Jul 12, 2019 5:01 pm UTC

p1t1o wrote:
cyanyoshi wrote:As I understand it, two objects in expanding space naturally move apart exponentially. Then you should be able to collect energy by lassoing an object a billion light-years away and gather the heat from friction as the rope slips through your hands....I think.


But the Joules of energy now in your hand, where are they taken from? Someplace must lose Joules, no?

Im aware of this: http://www.preposterousuniverse.com/blo ... conserved/

But something must change somewhere.

You are converting kinetic energy to electrical energy or whatever. In your reference frame, these galaxies are receding, and you are slowing parts of them down and using that energy.

Are not the atoms in the rope also pulled further apart, lengthening the rope at the same rate as universal expansion? But this would remove tension and any ability to extract work...

No, the distance between the atoms remains constant, just like the size of a galaxy remains constant. Only things extremely far away from us are receding, specifically things outside the Local Group of galaxies. I don't know a better way to explain this than to say that things closer than this are pulled away extremely weakly, too weakly to overcome the chemical bonds or whatever. But I've already said this a few times, so I guess I need a new approach.

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Re: Science fleeting thoughts

Postby Pfhorrest » Fri Jul 12, 2019 10:51 pm UTC

Eebster the Great wrote:There is no pressure gradient to exploit. The negative pressure is the same everywhere. Aside from that, to do work, something needs to move. If everything is stationary, work is zero.

But the sphere is not expanding along with the rest of the space under that pressure because it's held together by the electromagnetic interactions between its atoms, so relative to the expanding space, it's as though the sphere is actually contracting, similar to what you said about the larger cosmic sphere needing to have its constituent pieces all actually flying rapidly toward each other in order to stay the same size. Except since the sphere isn't literally contracting relative to itself, only relative to the expanding space it occupies, it can go on "contracting" forever, unlike an actually contracting sphere could, at least so long as the space keeps expanding.

And as it "contracts", everything it flows past could be used to do work, which would "slow down its contraction" (i.e. make it expand), yes, if the pieces were just coasting inertially toward each other, but they're held together by electromagnetic forces, so it's the same as if you were pumping stuff into the center of a normally stationary sphere in non-expanding space: yes, it would tend to push the pieces of the sphere apart, if it weren't for something holding it together, and since there is something holding it together, that energy that would otherwise have pushed it apart can be converted into another form.

It boils down to that the parts of a non-expanding object in an expanding spacetime are moving relative to that expanding spacetime, even though they seem to be stationary in a conventional sense, and that movement is what's exploited to do work.

Consider also another analogy: you have an elastic volume filled with air, and an airtight sphere inside that volume, and then you magically teleport new molecules of air evenly dispersed throughout that volume, causing the overall volume to expand. That would cause your sphere to expand too, and the general distances between everything floating in that air; except your sphere is made of rigid, inelastic stuff that doesn't want to expand. Because of that, the pressure inside the sphere increases relative to the exterior of it, even though the same moles of air were added inside and out, in a process similar to if the moles of air had stayed constant and the sphere had contracted. Coming back out of the analogy, we're obviously not adding new molecules of anything everywhere, but there is more energy coming into being evenly everywhere, so things that remain a constant size despite that and the resultant expansion of everything else end up with an energy gradient between their interior and exteriors, as though they had contracted. An immeasureably tiny energy gradient unless you're talking about ridiculously cosmic scales, but I am talking about those scales.
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Re: Science fleeting thoughts

Postby Eebster the Great » Sat Jul 13, 2019 7:10 am UTC

I feel like a lot of slightly different ideas keep getting mashed together, or you keep switching from one to the other. My point about not being able to exploit the pressure is that you can't just have a sphere surrounding a vacuum and gain energy from the vacuum. You can get energy from other things whizzing past the walls of the sphere. But as we pointed out earlier, you would also need all the walls to accelerate towards each other very quickly, just like the ends of the rope, and this will cause drag, and it's really not different from launching a rocket and using the drag from gas particles to run a generator.

The electromagnetic forces holding together your sphere are not going to magically be way better than the ones holding together the rope. Again, it's a problem of scale.

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Re: Science fleeting thoughts

Postby Pfhorrest » Sat Jul 13, 2019 8:40 am UTC

Electromagnetic forces are only holding together the sphere in the imaginary universe where the expansion of space is a lot higher than it is today, which was a thought experiment so that we could imagine measurable effects on the scale of structures that reasonably can be held together by electromagnetic forces, examining the scenario apart from the "rope won't hold together over hypergalactic distances" problem. We're talking about a sphere that's, say, five meters across, in a universe where the metric expansion of space is much much faster than it is now, but not quite fast enough to overcome the ordinary forces holding together an ordinary five meter sphere, and examining what could be done with that. Then we can talk about scaling up to a larger size to accomplish the same thing in a universe with a slower expansion like ours.
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