Science fleeting thoughts

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Re: Science fleeting thoughts

Postby Eebster the Great » Sat Jul 13, 2019 8:50 am UTC

Then yes, the gas in the sphere would be forced out through the sphere and could be used to generate energy the same way we use stream.

But eventually there would be no more gas in the sphere, so the lifetime energy generation is capped.

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Re: Science fleeting thoughts

Postby Pfhorrest » Sat Jul 13, 2019 9:13 am UTC

But there is still energy of some kind inside the sphere, because there is energy even in an "empty" vacuum, and new energy is constantly coming into being everywhere (and spreading out with the expanding space to maintain the same vacuum energy density), inside and outside the sphere both, but because of the expansion of space vs the fixed size of the sphere, there is a net flow of that energy from inside the sphere to outside. That was the point of the analogy about magically teleporting new air molecules in an even dispersion. We're not, of course, actually adding new molecules of anything, but there is nevertheless new energy coming into being in a geometrically similar fashion. I'm not really clear on exactly how one would go about harnessing that flow of vacuum energy, but it seems that there should very clearly be one. I do think that I recall reading something about some kind of radiation experienced by objects moving at relativistic speeds which was basically a consequence of vacuum energy doing weird relativistic things, so that seems like it would be one possible option, as each part of this "stationary" sphere would be "moving" at relativistic speeds relative to the expanding space. But it's past 2AM here and I can't remember much about that right now.

ETA: The Unruh effect.
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Re: Science fleeting thoughts

Postby Eebster the Great » Sat Jul 13, 2019 10:54 am UTC

The Unruh effect should cause the temperature of the vacuum to increase, but it's still a vacuum. You can't get energy from the vacuum, because that would require a state lower in energy than the lowest energy state.

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Re: Science fleeting thoughts

Postby ucim » Sat Jul 13, 2019 4:07 pm UTC

Eebster the Great wrote:Again, it's a problem of scale.
No, it's a question of principle. Mainly I think it's because we have only a vague shared understanding of what "expanding space" means. What is "distance", when space itself expands?

Also, we're musing under the assumption that universal constants are, well, constant. They could be tied to the "size" of space in some way (which would help explain why they are the values they are). If so, they could be tied to it in a manner that cancels out the energy gain from potential energy dependent on that constant.

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Re: Science fleeting thoughts

Postby gmalivuk » Sat Jul 13, 2019 8:04 pm UTC

ucim wrote:
Eebster the Great wrote:Again, it's a problem of scale.
No, it's a question of principle. Mainly I think it's because we have only a vague shared understanding of what "expanding space" means. What is "distance", when space itself expands?
Distances can be carefully defined even in an expanding universe.

Also, we're musing under the assumption that universal constants are, well, constant. They could be tied to the "size" of space in some way (which would help explain why they are the values they are). If so, they could be tied to it in a manner that cancels out the energy gain from potential energy dependent on that constant.

Which constants, specifically, would change the basic outcome if they turned out not to be constant?

If the distance between objects is changing, then in principle it's possible to extract energy from that change. This is true even in universes very different from our own, as long as they're expanding or contracting. Other facts about the universe might change how much energy can be extracted, or where that energy comes from, but I'm having a hard time imagining a universe consistent with what we know of the laws of physics in which it isn't possible.
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Re: Science fleeting thoughts

Postby Pfhorrest » Sat Jul 13, 2019 8:50 pm UTC

It sound to me like gmal at least agrees with the general principal I’m trying to establish here, so maybe he can venture a better stab at how in principle one might exploit that?

The broadest facts I’m going off of are just that space is expanding, and the vacuum energy is staying constant, so new energy is being created everywhere uniformly as space expands, which so far as I understand it is established science. Consequently, given a fixed volume within that expanding space, energy of some kind must be flowing from within that volume to outside it, just from simple geometry, which resultant energy gradient should in principle somehow be exploitable to do work. I’m unclear on the how to exploit it and how to build something that can do so especially at the scales required but the existence of that flow of energy from inside a volume to outside it, even if it’s just an empty universe with no matter and the volume is only abstractly demarcated, seems undeniable given the expansion of space and attendant creation of new energy.
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Re: Science fleeting thoughts

Postby Eebster the Great » Sat Jul 13, 2019 9:12 pm UTC

I don't think "flow of energy" is the right way to describe what's happening. There is no energy that was once within the sphere that is now outside it. Rather, energy has been created outside the sphere, but energy has not been created inside it. This is in fact what happens in galaxies.

gmalivuk is talking about a universe in which things are moving in the proper sense, that is, the proper distance between them is changing. This applies to the example of lassoing a distant galaxy cluster to exploit the kinetic energy of its recession, but it does not apply to the example of a rigid sphere held together by molecular bonds. In that case, nothing is actually moving, and thus no work is being done, and no energy can be extracted. Because vacuum energy is nonzero, as space expands, there is more vacuum, and thus more energy, but that doesn't mean there is any way to use this new energy. In order to use it, you would have to take some energy away from a vacuum somewhere, thus leaving it with even less energy than before. This contradicts the claim that it was a vacuum in the first place, which means the lowest possible energy level.

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Re: Science fleeting thoughts

Postby gmalivuk » Sat Jul 13, 2019 9:52 pm UTC

Pfhorrest wrote:
The broadest facts I’m going off of are just that space is expanding, and the vacuum energy is staying constant, so new energy is being created everywhere uniformly as space expands, which so far as I understand it is established science. Consequently, given a fixed volume within that expanding space, energy of some kind must be flowing from within that volume to outside it, just from simple geometry, which resultant energy gradient should in principle somehow be exploitable to do work.

No, that is not a consequence.

Current models have the density of vacuum energy constant in space, which means in fact that given a fixed volume within that space there's no change in the amount of vacuum energy. So I don't know why that means any energy is flowing anywhere.

(This is different from how matter and radiation behave, since their densities decrease as volume increases.)

The principle I agree with you on is that it's possible to extract energy, but the only way I've described that working is by exploiting the way metric expansion makes bits of matter behave relative to each other.
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Re: Science fleeting thoughts

Postby ucim » Sun Jul 14, 2019 12:30 am UTC

gmalivuk wrote:Distances can be carefully defined even in an expanding universe.
Thanks for that.
gmalivuk wrote:Which constants, specifically, would change the basic outcome if they turned out not to be constant?
I was thinking G, for example. If distance (whatever kind of distance is used for r in the gravitational formula) increases simply by virtue of the expansion of the universe , and G decreases by a proportional amount, then there is no "extra" gravitational potential energy caused by the masses "moving apart". But if while distance increases, comoving distance doesn't, and comoving distance is the... er... proper distance to use for r, then this would not be necessary.

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Re: Science fleeting thoughts

Postby Pfhorrest » Sun Jul 14, 2019 12:35 am UTC

Okay, let’s look at an even more simplified picture. You have two masses at relative rest some distance apart in an expanding and otherwise empty space, such that their gravitational attraction towards each other is exactly cancelled out by the expansion of the space between them, and they stay the same distance from each other. What does each mass experience that explains why it is “falling” toward the other and yet not getting any closer? Does it just seem like the gravity of the other is completely negated, or is there some force each experiences that counteracts gravity?
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Re: Science fleeting thoughts

Postby Eebster the Great » Sun Jul 14, 2019 1:24 am UTC

ucim wrote:
gmalivuk wrote:Which constants, specifically, would change the basic outcome if they turned out not to be constant?
I was thinking G, for example. If distance (whatever kind of distance is used for r in the gravitational formula) increases simply by virtue of the expansion of the universe , and G decreases by a proportional amount, then there is no "extra" gravitational potential energy caused by the masses "moving apart". But if while distance increases, comoving distance doesn't, and comoving distance is the... er... proper distance to use for r, then this would not be necessary.

This would only conserve energy if mass were uniformly distributed over space, which is true of dark energy but not of anything else. At any rate, it is not observed. And there is no a priori reason to expect energy to be conserved globally in GR (or even that such a thing could be possible).

Pfhorrest wrote:Okay, let’s look at an even more simplified picture. You have two masses at relative rest some distance apart in an expanding and otherwise empty space, such that their gravitational attraction towards each other is exactly cancelled out by the expansion of the space between them, and they stay the same distance from each other. What does each mass experience that explains why it is “falling” toward the other and yet not getting any closer? Does it just seem like the gravity of the other is completely negated, or is there some force each experiences that counteracts gravity?

Both masses are inertial in their own frame of reference. Remember that falling objects are actually not accelerating in Einstein's general theory of relativity. The space between these is not expanding, though it is expanding elsewhere. We would expect these things to warp space between them such that they "fall" towards each other if not for dark energy, yet instead we see a static spacetime between them where nothing happens. However, we can see a similar picture wherein they are held in place not by gravity but by a force such as the Coulomb force (if they have opposite charges). In that case, consider the frame of reference of one mass (not an inertial reference frame). In this frame, the mass really is accelerating toward the other mass exactly as Coulomb's law predicts. However, the other mass is accelerating away at the same rate, so it's not getting any closer. This cannot be explained without considering gravity, or I guess you'd call it antigravity here. It's the observable effect of dark energy.


BTW, my use of reference frames here is pretty far from precise. I guess you could call it an intuitive approach, but then again, nothing about this is really intuitive.

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Re: Science fleeting thoughts

Postby gmalivuk » Sun Jul 14, 2019 2:37 am UTC

ucim wrote:I was thinking G, for example. If distance (whatever kind of distance is used for r in the gravitational formula) increases simply by virtue of the expansion of the universe , and G decreases by a proportional amount, then there is no "extra" gravitational potential energy caused by the masses "moving apart". But if while distance increases, comoving distance doesn't, and comoving distance is the... er... proper distance to use for r, then this would not be necessary.

We would definitely notice if G changed that much over time.

Among other things, it would make orbits unstable within star systems. The scale factor of the universe was only about 60% of its present value 4 billion years ago.
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Re: Science fleeting thoughts

Postby Pfhorrest » Sun Jul 14, 2019 3:04 am UTC

I wasn’t forgetting that gravity doesn’t actually accelerate under relativity, but rather depending on it. If I am one of those masses and I jump into that universe with the other mass and start falling toward it and so feeling inertial and free floating as I get closer and closer to it, and then I push my magic button that turns on the expansion of space, and suddenly find myself no longer getting closer faster (lay “accelerating” but not properly accelerating) to the other mass, do I feel nothing to cause that change? It just seems like the other object suddenly has no mass to me?
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Re: Science fleeting thoughts

Postby gmalivuk » Sun Jul 14, 2019 4:56 am UTC

I mean, you might think it lost its mass, or you might do what astronomers actually did and think the universe was expanding.

After all, we observe things moving away from us when gravity would suggest they'd move toward us. I suspect there are also a number of things right near the boundary, with (near-)zero redshift without any Newtonian explanation for their unchanging distance.

Edit: For example, NGC 2976 has a redshift very near zero (zero is within the error bars), yet it's far enough away that Hubble's Law suggests it should be receding at 250 km/s.
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Re: Science fleeting thoughts

Postby ucim » Sun Jul 14, 2019 4:50 pm UTC

gmalivuk wrote:We would definitely notice if G changed that much over time.

Among other things, it would make orbits unstable within star systems. The scale factor of the universe was only about 60% of its present value 4 billion years ago.
Hmmm. What if we used logarithms?

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Re: Science fleeting thoughts

Postby gmalivuk » Sun Jul 14, 2019 4:57 pm UTC

The natural logorithm of the scale factor of the universe was only about 0.51 less than its present value Exp(22.11) years ago.
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Re: Science fleeting thoughts

Postby ucim » Sun Jul 14, 2019 5:53 pm UTC

gmalivuk wrote:The natural logorithm of the scale factor of the universe was only about 0.51 less than its present value Exp(22.11) years ago.
Uh.... 451.

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Re: Science fleeting thoughts

Postby Xanthir » Mon Jul 15, 2019 10:09 pm 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.

I don't think they need to be at right angles. On the balloon, you can perfectly well have a spool of wire in the 2d plane, connected to another anchor further away, and as space expands the expansion will cause the wire to unspool. No need for the spool to "stand up" in a third spatial dimension.
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Re: Science fleeting thoughts

Postby gmalivuk » Mon Jul 15, 2019 10:22 pm UTC

Right but Pfhorrest was talking about something different at that point.
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Re: Science fleeting thoughts

Postby Xanthir » Mon Jul 15, 2019 11:05 pm UTC

Ah, apologies then; I admit I was somewhat skimming at that point.
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Re: Science fleeting thoughts

Postby Pfhorrest » Tue Jul 16, 2019 8:55 am UTC

Yeah that 2D spindle has basically the same problem as the lassoo-a-distant-galaxy solution in that it depends on the linear motion of a finite object and so can't keep exploiting the unending expansion (of the balloon or of space) indefinitely. Eventually you run out of rope/spindle.

Even if my previous proposal has its flaws, it still seems to be that if there is an unending supply of new energy to the universe in the form of expanding space, there must be some way of taking continual advantage of that, and not just some one-off than runs out when you run out of rope/etc. I have new thoughts on that front from tonight but I don't feel like sharing them just now. I'd rather hear your better-informed ideas, which is why I asked the open-ended question to begin with.
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Re: Science fleeting thoughts

Postby Eebster the Great » Tue Jul 16, 2019 12:06 pm UTC

There is usable energy in the recession of the galaxies, but the expansion of space itself only increases the amount of vacuum energy. Just because there is more energy doesn't mean we can do anything with it. It's like increasing the temperature of both of two objects in thermal equilibrium equally. Sure, they now have more internal energy, but they are still in equilibrium. Or more closely, it's like increasing the number of such objects from 2 to 3. That's nice, but they are still in equilibrium, so there is still nothing to do.

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Re: Science fleeting thoughts

Postby Link » Tue Jul 23, 2019 3:37 pm UTC

SFT: I wonder what the topological classification of a human is. I was thinking "donut", because the digestive tract forms a continuous tube, but then I realised the nose also has two holes that are actually connected internally, and they connect to the mouth. (Of course, it's not particularly difficult to add an arbitrary number of holes to a human, so let's assume we're talking about an average person without piercings, birth defects, etcetera.)

It also makes me wonder if there's any interesting information to be gained from topological corrections to the spherical cow approximation. (And now I want to derive a bovine Dyson equation!)

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Re: Science fleeting thoughts

Postby p1t1o » Tue Jul 23, 2019 3:53 pm UTC

Link wrote:SFT: I wonder what the topological classification of a human is. I was thinking "donut", because the digestive tract forms a continuous tube, but then I realised the nose also has two holes that are actually connected internally, and they connect to the mouth. (Of course, it's not particularly difficult to add an arbitrary number of holes to a human, so let's assume we're talking about an average person without piercings, birth defects, etcetera.)

It also makes me wonder if there's any interesting information to be gained from topological corrections to the spherical cow approximation. (And now I want to derive a bovine Dyson equation!)


In my minds eye, I see a donut. Then I add nose, ear throat etc appertures. Now it looks like donu with a few extra holes connecting the main hole to another point on the surface.

Now topographically, I still think its a donut, though I dont know if Im technically correct.

But if I exaggerate the situation in order to get better visibility on the problem, by adding very many nose-ear-throat apertures, it now resembles something else quite accurately.

Humans are a foam.

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Re: Science fleeting thoughts

Postby DavidSh » Tue Jul 23, 2019 4:03 pm UTC

Human topology does depend on scale. The gut as one hole, and the nostrils as two more holes, are obvious. Tear ducts are smaller, but they do transport fluids between the eye socket and the nose. From what I read, there are two ducts per eye, so that would add four more holes. I've seen some suggestion that the Fallopian tubes actually open into the abdominal cavity, which would add another hole for many of us, but I'm not sure.

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Re: Science fleeting thoughts

Postby Link » Tue Jul 23, 2019 4:07 pm UTC

p1t1o wrote:
Now topographically, I still think its a donut, though I dont know if Im technically correct.
I don't think so. If you have, say, a Y-shaped hollow tube, there are more lines you can draw on it that can neither be continuously contracted to a point nor transformed into one another than there are on a donut. (Unless you're not dealing with an ISO standard donut, of course.)

p1t1o wrote:But if I exaggerate the situation in order to get better visibility on the problem, by adding very many nose-ear-throat apertures, it now resembles something else quite accurately.

Humans are a foam.
Ah, the "expand around infinity" approach. But now I'm no longer sure if it's a human or a Shoggoth we're considering.

DavidSh wrote:
Human topology does depend on scale. The gut as one hole, and the nostrils as two more holes, are obvious. Tear ducts are smaller, but they do transport fluids between the eye socket and the nose. From what I read, there are two ducts per eye, so that would add four more holes. I've seen some suggestion that the Fallopian tubes actually open into the abdominal cavity, which would add another hole for many of us, but I'm not sure.
That makes sense, actually.

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Moo = M(- + -o- + -o-o- + -o-o-o- + ...)

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Re: Science fleeting thoughts

Postby Sizik » Tue Jul 23, 2019 4:44 pm UTC

Y-shaped tube (3 openings) is equivalent to a donut with two holes. I assume the pattern of n openings = (n-1)-holed torus continues, but that could be wrong.
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Re: Science fleeting thoughts

Postby Sableagle » Tue Jul 23, 2019 4:50 pm UTC

Link wrote:SFT: I wonder what the topological classification of a human is. I was thinking "donut", because the digestive tract forms a continuous tube, but then I realised the nose also has two holes that are actually connected internally, and they connect to the mouth. (Of course, it's not particularly difficult to add an arbitrary number of holes to a human, so let's assume we're talking about an average person without piercings, birth defects, etcetera.)

It also makes me wonder if there's any interesting information to be gained from topological corrections to the spherical cow approximation. (And now I want to derive a bovine Dyson equation!)


The answer must depend on the scale of the measuring ball. To a beach ball, a human is topologically a ball. To a fine sand grain, nostrils and tear ducts all count. To a subluminal neutron, a human can be considered as a cloud of low-opacity blobs.
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Re: Science fleeting thoughts

Postby cyanyoshi » Tue Jul 23, 2019 7:24 pm UTC

Sizik wrote:Y-shaped tube (3 openings) is equivalent to a donut with two holes. I assume the pattern of n openings = (n-1)-holed torus continues, but that could be wrong.

Perhaps, but I'm not sure how the circulatory system changes things. What happens if your blood vessels make a knot? Does this even happen?

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Re: Science fleeting thoughts

Postby Eebster the Great » Tue Jul 23, 2019 7:32 pm UTC

"Donut" is not an actual topological term. "Torus" is the word you're looking for.

Surfaces of humans have a genus much greater than 1 (lots of little holes), but humans themselves are 3-dimensional, so it doesn't make much sense to call us surfaces anyway.

It does not matter if your vessels make a knot, at least in terms of classifying your topology.

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Re: Science fleeting thoughts

Postby Heimhenge » Tue Jul 23, 2019 9:36 pm UTC

cyanyoshi wrote:
Sizik wrote:Y-shaped tube (3 openings) is equivalent to a donut with two holes. I assume the pattern of n openings = (n-1)-holed torus continues, but that could be wrong.

Perhaps, but I'm not sure how the circulatory system changes things. What happens if your blood vessels make a knot? Does this even happen?


I was once told by a doctor that a sonogram indicated "tortuous carotids" and had to ask what he meant (it didn't sound good). He explained that the carotids are never like in the anatomy books, running straight up the sides of the neck into the brain. They always wander around in a circuitous path, but mine were more circuitous than average.

I'd be surprised if veins/arteries could grow into a knot. If so, there's probably a medical name for it since it would seem to be a serious defect. Might possibly happen with the smaller capillaries though. Ask your doctor. :)

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Re: Science fleeting thoughts

Postby Eebster the Great » Wed Jul 24, 2019 2:47 am UTC

"Tortuous" has always sounded too similar to "Torturous" for my liking.

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Re: Science fleeting thoughts

Postby Angua » Wed Jul 24, 2019 8:03 am UTC

Heimhenge wrote:
cyanyoshi wrote:
Sizik wrote:Y-shaped tube (3 openings) is equivalent to a donut with two holes. I assume the pattern of n openings = (n-1)-holed torus continues, but that could be wrong.

Perhaps, but I'm not sure how the circulatory system changes things. What happens if your blood vessels make a knot? Does this even happen?


I was once told by a doctor that a sonogram indicated "tortuous carotids" and had to ask what he meant (it didn't sound good). He explained that the carotids are never like in the anatomy books, running straight up the sides of the neck into the brain. They always wander around in a circuitous path, but mine were more circuitous than average.

I'd be surprised if veins/arteries could grow into a knot. If so, there's probably a medical name for it since it would seem to be a serious defect. Might possibly happen with the smaller capillaries though. Ask your doctor. :)

Arterio-venous malformation.

Haemangioma

Not exactly knots I suppose, but similar.
DavidSh wrote: I've seen some suggestion that the Fallopian tubes actually open into the abdominal cavity, which would add another hole for many of us, but I'm not sure.

They do.

Eustachian tubes might also count if you disregard the ear drum?
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Re: Science fleeting thoughts

Postby Xanthir » Wed Jul 24, 2019 4:58 pm UTC

You can't disregard the ear drum! We're not, just, making things up here!
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Re: Science fleeting thoughts

Postby Pfhorrest » Wed Jul 24, 2019 5:07 pm UTC

Ear drums can be punctured, and if fallopian tubes count it must only be after the hymen has been punctured, so eustachian tubes can count just as much as those.
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Re: Science fleeting thoughts

Postby Angua » Wed Jul 24, 2019 5:33 pm UTC

Xanthir wrote:You can't disregard the ear drum! We're not, just, making things up here!

I wasn't certain because you can get perforated ear drums from infections?
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Re: Science fleeting thoughts

Postby gmalivuk » Wed Jul 24, 2019 5:35 pm UTC

Pfhorrest wrote:Ear drums can be punctured, and if fallopian tubes count it must only be after the hymen has been punctured, so eustachian tubes can count just as much as those.

Imperforate hymens are very rare and can cause problems for people who have them.

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Re: Science fleeting thoughts

Postby Xanthir » Fri Jul 26, 2019 11:13 pm UTC

Simplifying what gmal just said: normally hymens are *not* a total seal, they're just a flesh ring with a *smaller* opening than the whole vagina. (Otherwise you can't menstruate!)

So no, hymen doesn't change your hole count.
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Re: Science fleeting thoughts

Postby sophyturtle » Sat Jul 27, 2019 12:32 am UTC

Especially for those who never had one.
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Re: Science fleeting thoughts

Postby KittenKaboodle » Sat Jul 27, 2019 1:15 am UTC

Xanthir wrote:Simplifying what gmal just said: normally hymens are *not* a total seal, they're just a flesh ring with a *smaller* opening than the whole vagina. (Otherwise you can't menstruate!)

So no, hymen doesn't change your hole count.

True, but not because imperforate hymens are rare, it is that the vagina/uterus/Fallopian-tubes/abdominal-cavity are topographically just a dimple, not a hole, aren't they?

A couple of interesting animations at: https://en.wikipedia.org/wiki/Topology turning a mug into a doughnut (torus) the inside of the mug just disappears, the loop of the handle becomes the hole, but also they turn a cow into a sphere, not a doughnut! But as someone else has said, it depends on scale, mathematically there is no limit on how small the hole in a torus is, so a doughnut can be a "sphere" just as well as a cow can be. And a cow can be a hula-hoop even better than it can be a sphere.

Also, a round earth can be a pancake (or taking some liberties, a cow) just as well as a flat earth can be an oblate spheroid! so take that that all you flat earth deniers!


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