Search found 434 matches

by lgw
Mon Nov 28, 2016 7:45 pm UTC
Forum: Science
Topic: Toroidal star
Replies: 14
Views: 2490

Re: Toroidal star

Also, you could cheat this I think with dark matter - does it count as a torus if the donut hole is a blob of dark matter rather than being empty? Keep in mind that dark matter does not have an electric charge. The thing that allows you to hold stuff in your hand is electromagnetism - the electron ...
by lgw
Mon Nov 28, 2016 7:36 pm UTC
Forum: Science
Topic: Can you build a better thermos than empty space?
Replies: 4
Views: 1931

Re: Can you build a better thermos than empty space?

Thanks for the reply. A big thermos can maintain a larger temperature difference against the cooling CMBR outside, but there's no size at which the thermos won't cool down. Ah, sure, but the universe keeps cooling down, so as long as the thermos cools slower, it will always be warmer, right? I'm hav...
by lgw
Sun Nov 20, 2016 9:35 pm UTC
Forum: Science
Topic: Is entanglement that surprising?
Replies: 27
Views: 4741

Re: Is entanglement that surprising?

What is important is that, for entangled particles, the strength of this correlation is STRONGER than would be classically allowed. This is a subtle point, and in the end I think a little frustrating because it seems like it just boils down to a quantitative difference in how the particles behave r...
by lgw
Sun Nov 20, 2016 8:44 pm UTC
Forum: Science
Topic: Toroidal star
Replies: 14
Views: 2490

Re: Toroidal star

The problem, as I understand it, is that maintaining a toroidal shape would require a net outward force that is greater closer to the center than it is farther away. Unfortunately, rotation and gravity do not work that way. The only force that I can imagine holding a stellar mass in such a shape is...
by lgw
Sun Nov 20, 2016 2:36 am UTC
Forum: Science
Topic: Can you build a better thermos than empty space?
Replies: 4
Views: 1931

Can you build a better thermos than empty space?

The universe is cooling - slowly now, but quickly in the early days. It is theoretically possible to make a thermos (well, some sort of vast Dewer jar with very reflective surfaces), filled with material at the temperature of the CMBR, such that the contents cool slower than the expanding universe? ...
by lgw
Tue Sep 15, 2015 9:16 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1576: "I Could Care Less"
Replies: 310
Views: 35725

Re: 1576: "I Could Care Less"

I used "I could care less" as a form of nerd sniping for years, but these days I like "I give approximately 0 fucks about that" better. For the record, I do thing there are right and wrong in language, and if I explain it only as "(stated to be) thought wrong", then tha...
by lgw
Tue Sep 08, 2015 8:46 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1574: "Trouble for Science"
Replies: 41
Views: 9124

Re: 1574: "Trouble for Science"

This might be like Franklin's lightning and kite experiment. The first experimenter got lucky, but some of those that try to repeat it die. Franklin wrote up his experiment for the Royal Society. The write up starts with a list of steps for safety, as other experimenters had died. Franklin's lightn...
by lgw
Sun May 10, 2015 2:59 am UTC
Forum: Mathematics
Topic: Topology terminology question
Replies: 22
Views: 2640

Re: Topology terminology question

Thanks everyone - this will take me some time to think through. I started with this question just looking for terms for possible shapes of the universe (the kind where you might see your location in a good enough telescope vs not), but one wiki walk later, I know far less than I started with! :D For...
by lgw
Sat May 09, 2015 11:15 pm UTC
Forum: Mathematics
Topic: Topology terminology question
Replies: 22
Views: 2640

Re: Topology terminology question

Sorry, let me ask the questions a different way - I'm probably asking in a silly way. 1) "What do a sphere, a torus, and a Klein bottle all have in common (but a plane doesn't)?" 2) "What do those things, a bounded region, and a manifold with a bounded metric all have in common?"...
by lgw
Sat May 09, 2015 6:51 pm UTC
Forum: Mathematics
Topic: Topology terminology question
Replies: 22
Views: 2640

Re: Topology terminology question

Thanks for the reply. Between terms like compact, complete, and bounded, I'm looking for the right term for the concept "there exists some maximum distance that no two points can exceed" in the general sense across manifolds and metrics (from a finite Euclidian region, to a torus, to a cra...
by lgw
Sat May 09, 2015 6:06 pm UTC
Forum: Mathematics
Topic: Topology terminology question
Replies: 22
Views: 2640

Topology terminology question

I'm confused about terminology relating to Topology, and can't find anything in Wikipedia to set me straight (as is often the case, the articles assume you know too much about the field), so maybe you guys can help. Between terms like compact, complete, and bounded, I'm looking for the right term fo...
by lgw
Sun Feb 01, 2015 7:10 pm UTC
Forum: Science
Topic: Making a Black Hole with Light
Replies: 8
Views: 2416

Re: Making a Black Hole with Light

Suppose that you had so many stars that in whatever direction you looked you saw the surface of a star at a temperature of 5,778 K. Then you would soon warm up to 5,778 K. The thing is though that the second law of thermodynamics says that focusing isn't going to get you a higher temperature, so pr...
by lgw
Sun Jan 25, 2015 8:57 pm UTC
Forum: Science
Topic: Making a Black Hole with Light
Replies: 8
Views: 2416

Making a Black Hole with Light

What if you could focus all the light from the Sun, or from some number of stars, sharply enough to create a black hole at the focus. This would be a fun addition to discussions about radiative thermal equilibrium (" technically , if you focus the light sharply enough, it's actually much cooler...
by lgw
Fri Oct 31, 2014 8:12 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1441: Turnabout
Replies: 44
Views: 11390

Re: 1441: Turnabout

The Earth rotates at nearly 2.8 megafurlongs/fortnight at the equator. In the 2.6 seconds it would take your shot to reflect off the moon, you'd have moved 6 furlongs (over a kilometer, for those using deprecated units), at the equator, or a fair portion of that at temperate latitudes. Sorry, Randal...
by lgw
Fri Oct 10, 2014 7:43 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1432: "The Sake of Argument"
Replies: 203
Views: 27268

Re: 1432: "The Sake of Argument

Is it just me, or is Randall starting to exhibit the symptoms of the SJW-plague? I don't want XKCD to go in the direction of Sinfest... Yeah, because if there's one thing plaguing the Internet these days, it's definitely a desire for too much justice . Like, do you not get how much it sounds like y...
by lgw
Wed Sep 24, 2014 10:11 pm UTC
Forum: Science
Topic: Black Hole Thought Experiment
Replies: 15
Views: 3971

Re: Black Hole Thought Experiment

Let's say you make a black hole where all the needed mass is in the shell... Just FYI, this really isn't possible. If we somehow move all the matter in the Earth into a thin shell at the surface, then as you note, spacetime in the hollow interior is basically flat. But we do have a small engineerin...
by lgw
Wed Sep 24, 2014 9:57 pm UTC
Forum: Science
Topic: Bell's Inequality Experiments Question
Replies: 4
Views: 2266

Bell's Inequality Experiments Question

I've been following the mounting evidence for Bell's Theorem from experiments over the past couple of years, but I don't quite understand the experiment. When a pair of entangled photons are measured for polarization (or electrons for spin polarization, same deal), the predicted results are the same...
by lgw
Tue Sep 23, 2014 11:43 pm UTC
Forum: Science
Topic: Black Hole Thought Experiment
Replies: 15
Views: 3971

Re: Black Hole Thought Experiment

Let me explain more what motivates this thought experiment: I'm poking at the oddity that GR requires that being inside a distant uniform shell of matter can have an extreme effect on local conditions, in stark contrast to classical expectation (after all, classically that would have 0 effect). Why...
by lgw
Mon Sep 22, 2014 8:23 pm UTC
Forum: Science
Topic: Fuck Dark Matter; It's a sprinkler, not a whirlpool.
Replies: 135
Views: 22221

Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

And as I mentioned, earlier in this post , a statistical mechanics analysis suggests that even if they can collide, the net effect would tend to be to knock them into higher orbits or escape trajectories if not for the fact that collisions can also cause them to lose energy to radiation of some kin...
by lgw
Sun Sep 21, 2014 1:16 am UTC
Forum: Science
Topic: Black Hole Thought Experiment
Replies: 15
Views: 3971

Re: Black Hole Thought Experiment

Thanks for the responses everyone! Let me explain more what motivates this thought experiment: I'm poking at the oddity that GR requires that being inside a distant uniform shell of matter can have an extreme effect on local conditions, in stark contrast to classical expectation (after all, classica...
by lgw
Sat Sep 20, 2014 12:12 am UTC
Forum: Science
Topic: Black Hole Thought Experiment
Replies: 15
Views: 3971

Black Hole Thought Experiment

Let's make a black hole - a big one. One light year in radius to be exact. (This requires about ~5x the mass of our galaxy, so such a thing could technically exist.) Further, let's make it carefully out of only dark matter, all set up in a series of orbitally-stable halos (shells) of as close to uni...
by lgw
Fri Sep 19, 2014 11:46 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2846
Views: 551354

Re: RELATIVITY QUESTIONS! (and other common queries)

We only call the kind that carries energy away a gravitational wave. And even then, gravitational waves are just the linear perturbation of a metric. GR is full of awesome nonlinear things. Thanks for the explanation! So there's nothing particle-like about the energy-carrying one? (Gravitons are th...
by lgw
Thu Sep 18, 2014 10:00 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2846
Views: 551354

Re: RELATIVITY QUESTIONS! (and other common queries)

I've always been confused by gravity waves. When an electron moves, there are two kinds of waves possible: ⋅  The "information wave" as the new location of the charge spreads (which I guess is a "real" wave if there's a nearby dielectric to re-orient), but this does no ...
by lgw
Wed Sep 17, 2014 7:55 pm UTC
Forum: Science
Topic: [Mech eng.] Feasibility of an omnidirectional wheelchair?
Replies: 28
Views: 5361

Re: [Mech eng.] Feasibility of an omnidirectional wheelchair

For a powered caster wheelchair, you could have the casters on movable arms that allow the chair to 'step' up and down stairs and other obstacles For occasional off-road use, you can also go with the tachikoma approach - basically fully articulate legs with wheels on the end that can be folded out ...
by lgw
Mon Sep 15, 2014 6:30 pm UTC
Forum: Science
Topic: what to study to be a string theorist?
Replies: 9
Views: 2892

Re: what to study to be a string theorist?

For those of us who are a bit older, the Stanford continuing education series in physics will eventually get you to an understanding, if you have the math. https://www.youtube.com/watch?v=pyX8kQ-JzHI&list=PL10169D920B3A7B5A Going through this now myself. Silly as it seems to think you could lear...
by lgw
Sat Sep 13, 2014 5:27 pm UTC
Forum: Science
Topic: [Mech eng.] Feasibility of an omnidirectional wheelchair?
Replies: 28
Views: 5361

Re: [Mech eng.] Feasibility of an omnidirectional wheelchair

Smartass chairs don't have engines, though. I don't think I've seen that type of wheel in a self-propelling vehicle. Motorized casters are completely reasonable for light loads. Hub motors in the wheels, with additional motors that "point" the wheels, are a very practical solution. With t...
by lgw
Fri Sep 12, 2014 5:56 pm UTC
Forum: Science
Topic: A proof that hyperspace cannot transport matter
Replies: 26
Views: 5164

Re: A proof that hyperspace cannot transport matter

There's no proposal for a wormhole which "magics" something from one place to another. It would move across a nice smooth curved manifold, just one that has weird wormhole shapes. But the gravity (and gravitational potential energy) would just smoothly move from one end to the other. It w...
by lgw
Wed Sep 10, 2014 7:26 pm UTC
Forum: Science
Topic: FTL communication and time travel
Replies: 51
Views: 12046

Re: FTL communication and time travel

The universe most likely is infinite though. The observable universe has a center of mass, but why should the laws of physics care about that? We might like to talk about it, but we can't assign it any unique significance. if the universe is non-infinite, there would have to be a center of mass, ye...
by lgw
Thu Sep 04, 2014 11:56 pm UTC
Forum: Science
Topic: FTL communication and time travel
Replies: 51
Views: 12046

Re: FTL communication and time travel

I'm sure I saw the term before Card, but damned if I can remember where. Heinlein invented so many SF terms that became widely used, but not this one. I have noticed that a few people have this strong aversion to the word that I can't explain. It's certainly not tied to Card! There's not a better wo...
by lgw
Fri Aug 29, 2014 11:43 pm UTC
Forum: Science
Topic: Gravitational waves, potential, and creationism
Replies: 11
Views: 3053

Re: Gravitational waves, potential, and creationism

Tyndmyr wrote:My guess is that they'll simply twerk it in some way to claim that god totally set up the gravity to already be visible to us as well.


And thus Tyndmyr's Theory of Twerking was born. The jiggling is evidence of gravity waves sent by God to make us happy. I'm a believer.
by lgw
Fri Aug 29, 2014 8:03 pm UTC
Forum: Science
Topic: FTL communication and time travel
Replies: 51
Views: 12046

Re: FTL communication and time travel

The preferred ansible frame could be preexisting, or it could be a creation of the ansibles: The frame is created once the ansibles turn on, determined by their motion, and eventually disappears. Two ansible networks would become entangled whenever they causally connect. Once entangled, the maximum...
by lgw
Thu Aug 28, 2014 4:00 am UTC
Forum: Science
Topic: FTL communication and time travel
Replies: 51
Views: 12046

Re: FTL communication and time travel

I believe that if *all* ansibles have to be comoving, that essentially sets up a privileged rest frame and maintains causality. And it's worth noting that while relativity eliminates any requirement for a privileged rest frame, you have the freedom to pick one if needed for some other theory. As a ...
by lgw
Thu Aug 28, 2014 3:34 am UTC
Forum: Science
Topic: Fuck Dark Matter; It's a sprinkler, not a whirlpool.
Replies: 135
Views: 22221

Re: Fuck Dark Matter; It's a sprinkler, not a whirlpool.

Droplets flung from a sprinkler have very little angular momentum, right? They only look like they're spinning because of the emission pattern? They're not strictly radial, but they move in a straight line away from a point very close to the axis of the sprinkler? Even with frame dragging, you can't...
by lgw
Mon Aug 25, 2014 8:15 pm UTC
Forum: Science
Topic: Does the universe have "Garden of Eden" configurations?
Replies: 24
Views: 5186

Re: Does the universe have "Garden of Eden" configurations?

That is a looser notion of "Garden of Eden" than what is actually meant by the term. OK, fair enough, but I was thinking "the laws of physics are time-reversible, so: no" had been talked to death for the narrow sense. There are a variety of complex configurations in various cell...
by lgw
Sun Aug 24, 2014 11:35 pm UTC
Forum: Science
Topic: Holomorpic vs Holograpic
Replies: 7
Views: 2604

Holomorpic vs Holograpic

As I understand it, the holographic principle says that the maximum information in a space is limited by the surface area of a boundary of that space, and thus in principle could be encoded on that boundary, as revealed by the entropy of a black hole. I found that surprising, but maybe I shouldn't h...
by lgw
Sun Aug 24, 2014 9:57 pm UTC
Forum: Science
Topic: Does the universe have "Garden of Eden" configurations?
Replies: 24
Views: 5186

Re: Does the universe have "Garden of Eden" configurations?

In physics, a "Garden of Eden" is simply the consequence of any conservation law. Neat, right? If mass is conserved, then the same laws of physics work for various total masses in the system, but a total mass of 3 cannot by any means evolve into a total mass of 2 or 4 or pi. If momentum is...
by lgw
Sat Aug 23, 2014 1:04 am UTC
Forum: Science
Topic: Why is it hard to get things cold?
Replies: 15
Views: 3845

Re: Why is it hard to get things cold?

I think the difference between why it's easy to heat something but hard to cool it is because it's apples and oranges, technologically. We can make a heat engine that uses work to make a thermal difference between two reservoirs, sure, and you can have your "target area" to be heated or c...
by lgw
Mon Aug 18, 2014 2:37 am UTC
Forum: Science
Topic: Stimulated emission and no-cloning theorem
Replies: 8
Views: 3226

Re: Stimulated emission and no-cloning theorem

You can't clone all of the quantum information, but you can clone some of it. Stimulated emission was actually the first way this way this was done.

Partial cloning - what could possibly go wrong?

mini-me-2.gif
by lgw
Sat Aug 16, 2014 5:55 pm UTC
Forum: Science
Topic: Does acceleration increase rest mass?
Replies: 29
Views: 5475

Re: Does acceleration increase rest mass?

Well, one thing to clear up: there's an often-taught, always-wrong notion that mass increases at relativistic velocities, as a misunderstanding of the momentum increase (as seen from a frame in which the object is moving close to c) and misguided attempt to explain why you can't reach the speed of l...
by lgw
Sat Aug 16, 2014 12:45 am UTC
Forum: Science
Topic: Dark Matter
Replies: 27
Views: 5333

Re: Dark Matter

I've been amusing myself with the idea that there are 10 or 20 kinds of dark matter, each fundamentally different in some way. For example, matter with analogs to the proton and electron, but bound so tightly that at present energy levels, or even at the energy levels present when the universe was 1...

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