Search found 2201 matches

by thoughtfully
Sun Sep 13, 2015 1:53 am UTC
Forum: Science
Topic: Homo naledi: Another link
Replies: 21
Views: 3272

Re: Homo naledi: Another link

I think it says more about what they view as counting as justification than anything else.
by thoughtfully
Sun Jul 26, 2015 9:28 pm UTC
Forum: Science
Topic: Boiling the oceans off
Replies: 5
Views: 1681

Re: Boiling the oceans off

The Sun's output increases very slowly with time. Long before it becomes a red giant and the neighborhood really heats up, it will be warm enough to boil off the oceans. The estimated figure is around a billion years hence; five billion to red giant evolution. So you could just wait. http://www.skep...
by thoughtfully
Thu Jul 16, 2015 6:43 pm UTC
Forum: Science
Topic: Pluto down, next stop...interstellar?
Replies: 30
Views: 6268

Re: Pluto down, next stop...interstellar?

Far away from habitation or anything else you don't want irradiated, a nuclear salt water rocket is probably a good bet for combining ridiculous amounts of thrust and specific impulse. Cheers! http://www.projectrho.com/public_html/rocket/enginelist.php#id--Nuclear_Thermal--Gas_Core--Open_Cycle--Nucl...
by thoughtfully
Wed Jul 15, 2015 4:03 pm UTC
Forum: Science
Topic: Problem about travelling backwards
Replies: 15
Views: 3338

Re: Problem about travelling backwards

Energy Conservation doesn't really apply always. Energy is poorly defined in General Relativity at cosmological scales, for instance. Light redshifted by the expansion of the Universe loses energy, but it doesn't seem to add to the balance anywhere else, for instance. It could be the same way with u...
by thoughtfully
Thu Jul 09, 2015 2:40 am UTC
Forum: Science
Topic: Problem about travelling backwards
Replies: 15
Views: 3338

Re: Problem about travelling backwards

My take on it is that history only happens once. You can intersect with your worldline in the past, but you already know what you're going to do (provided that you actually observed it; the point is that it's happened). This is the essential trouble with CTCs. Past and future are muddled, and not re...
by thoughtfully
Sun Jun 28, 2015 3:31 pm UTC
Forum: Science
Topic: Why are plants not black
Replies: 8
Views: 2241

Re: Why are plants not black

Presumably there's no fitness-enhancing path between the pigments they have and the ones that are missing. There's lots of obvious stuff missing in nature.
by thoughtfully
Fri Jun 12, 2015 11:42 pm UTC
Forum: Science
Topic: Cannibals and kuru resistance
Replies: 4
Views: 1918

Re: Cannibals and kuru resistance

The host's necessity to remain alive evolutionarily-speaking goes down quite a bit after reproductive age. Lots of species have evolved to die quite soon after reproducing, in order to optimize resources for the offspring, for instance, and there is plenty of speculation that there may be some sort ...
by thoughtfully
Mon Jun 01, 2015 4:29 pm UTC
Forum: Coding
Topic: Useful applications of recursion?
Replies: 19
Views: 5671

Re: Useful applications of recursion?

I don't know if this qualifies as useful , but I once combined recursion with lazy evaluation to obtain an iterator for the columns of Pascal's Triangle. For instance, f(0) produces 1,1,1,1..., f(1) the Whole Numbers, f(2) the Triangular Numbers, and f(3) Tetrahedral Numbers. def pascol(n): if n == ...
by thoughtfully
Fri May 15, 2015 3:56 pm UTC
Forum: Science
Topic: Mirror Question from my daughter
Replies: 6
Views: 2228

Re: Mirror Question from my daughter

Check out some of the earlier threads on the topic.
by thoughtfully
Tue May 12, 2015 6:23 pm UTC
Forum: Science
Topic: Equilibrium and Thermodynamics
Replies: 3
Views: 1715

Re: Equilibrium and Thermodynamics

Is there is a similar flaw with using processes like autoionization. If you have gas AB between two charged plates, the mass action expression says the endothermic reaction AB -> A+ and B- will occur to a small extent. But those ions will be attracted to the plates. A clever system could collect th...
by thoughtfully
Sun May 10, 2015 4:06 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2962
Views: 729663

Re: Relativity, Acceleration, and Gravity

I'm not exactly a science wiz, so correct me if I'm wrong: The Equivalence Principle states that gravity is physically identical to acceleration. Carlington's post is excellent, but I just want to clarify a couple of of things. The equivalence principle only applies locally . This means with respec...
by thoughtfully
Thu May 07, 2015 5:22 pm UTC
Forum: Science
Topic: If the earth was made of TNT...
Replies: 18
Views: 3943

Re: If the earth was made of TNT...

That's TNT. The math we used doesn't care about configuration or anything complicated. It's the same ratio for a gram as for a planet.
by thoughtfully
Thu May 07, 2015 5:15 pm UTC
Forum: Science
Topic: If the earth was made of TNT...
Replies: 18
Views: 3943

Re: If the earth was made of TNT...

I used SI units, so kg for mass, and m/s for velocity, so you did also. The numeric values will take care of themselves if you stick to one system of units.
by thoughtfully
Thu May 07, 2015 5:05 pm UTC
Forum: Science
Topic: If the earth was made of TNT...
Replies: 18
Views: 3943

Re: If the earth was made of TNT...

You have E=Mc2, and E is the joules released.
by thoughtfully
Thu May 07, 2015 4:30 pm UTC
Forum: Science
Topic: If the earth was made of TNT...
Replies: 18
Views: 3943

Re: If the earth was made of TNT...

Let's start with the gravitational binding energy of the Earth. This is only a rough approximation, as it does not account for varying density with depth or any chemical binding energy. I kinda doubt TNT is stable when configured in a sphere of that size. But we can ignore that. U = 3/5 GM 2 /R The ...
by thoughtfully
Tue May 05, 2015 1:44 pm UTC
Forum: Science
Topic: Deadlifter
Replies: 17
Views: 4446

Re: Deadlifter

The dimples in golf balls create lift as the ball spins. Something like that could help a little, but at supersonic speeds and in thin air? Seems like it couldn't be much. Firing something expendable slightly ahead of the payload might get one somewhere. To make it really interesting, ionize the tra...
by thoughtfully
Mon May 04, 2015 12:05 pm UTC
Forum: Science
Topic: Molten salt reactors
Replies: 19
Views: 9809

Re: Molten salt reactors

Another obstacle I've heard of in the context of liquid fuel reactors is that fuel assemblies are a major, maybe the major, source of revenue for nuclear companies.
by thoughtfully
Wed Apr 29, 2015 9:05 pm UTC
Forum: Science
Topic: Constants and physical significance
Replies: 12
Views: 3454

Re: Constants and physical significance

The ones that come to mind are the 21 cm Hydrogen spectral line and the distance light travels in a nanosecond (c * 1e-9 s = 2.99792458e-1 m = .983571 foot) A nanosecond is a bit outside the realm of experience, but the interval between CPU cycles in modern computers and smart phones is of that order.
by thoughtfully
Wed Apr 29, 2015 3:54 pm UTC
Forum: Science
Topic: Light, mass, and gravity
Replies: 30
Views: 4591

Re: Light, mass, and gravity

I just went back and saw that, oops! My coffee tank is still too low.
by thoughtfully
Wed Apr 29, 2015 1:30 pm UTC
Forum: Science
Topic: Light, mass, and gravity
Replies: 30
Views: 4591

Re: Light, mass, and gravity

Newton's law of universal gravitation says that the force (F) of gravitational attraction between two objects with Mass1 and Mass2 at distance D is: F = G(mass1*mass2)/D squared Photons have zero mass. If you substitute 0 in as mass2: F = G(mass1*0)/D squared F = 0 However, photons are affected by ...
by thoughtfully
Fri Apr 24, 2015 10:24 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2962
Views: 729663

Re: RELATIVITY QUESTIONS! (and other common queries)

This still amazes me. Almost, just almost, crazier than a black hole.
by thoughtfully
Thu Apr 23, 2015 3:00 pm UTC
Forum: Science
Topic: Is the 3 body problem particularly hard?
Replies: 4
Views: 2027

Re: Is the 3 body problem particularly hard?

If you like having your mind warped, try this:
http://www.preposterousuniverse.com/blo ... /n-bodies/

Follow the links within for maximum bendery.
Spoiler:
N=20
Image
by thoughtfully
Thu Apr 02, 2015 7:21 pm UTC
Forum: Science
Topic: Teleporting inside a wall
Replies: 16
Views: 5363

Re: Teleporting inside a wall

To make predictions, you need a model/theory, not just "magic".
by thoughtfully
Wed Apr 01, 2015 3:25 pm UTC
Forum: Science
Topic: Ad Astra takes on SPAAAAAAAAACE
Replies: 6
Views: 2033

Re: Ad Astra takes on SPAAAAAAAAACE

The neat thing about VASIMR is the "V" part, which stands for "variable". It can vary the thrust vs efficiency prameters to suit changing conditions through the course of a mission. What's the extent of the variable range? The Atomic Rocket site suggests a factor of ten, althoug...
by thoughtfully
Wed Apr 01, 2015 1:20 pm UTC
Forum: Science
Topic: Ad Astra takes on SPAAAAAAAAACE
Replies: 6
Views: 2033

Re: Ad Astra takes on SPAAAAAAAAACE

Also, it isn't just ion engines. Any rocket (a device that obtains thrust by spitting out propellant, as opposed to using an external source, like a light sail) is going to trade off thrust with specific impulse. Thrust is necessary for getting out of gravity wells, but other than that, a rocket des...
by thoughtfully
Wed Apr 01, 2015 1:32 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2962
Views: 729663

Re: RELATIVITY QUESTIONS! (and other common queries)

2) A light ray is a straight line, not a wiggle through space, so there isn't really anything exactly equivalent. Is that true, though? What about diffraction, double slit and all the other wavey stuff then, how does that work? Gravity's special. Certainly when in the famework of General Relativity...
by thoughtfully
Sun Mar 01, 2015 1:57 am UTC
Forum: Science
Topic: Oxidisers
Replies: 30
Views: 7407

Re: Oxidisers

Quick recap:
Oxygen is the prototypical oxidizing agent. Oxygen is way out on the right side of the periodic table, so it accepts electrons in order to get a full shell.
Ergo, oxidizers accept negative charge / donate positive charge.
by thoughtfully
Thu Feb 26, 2015 3:28 am UTC
Forum: Science
Topic: Planck density and mass-energy conservation
Replies: 25
Views: 5813

Re: Planck density and mass-energy conservation

"Pixelated" space/time makes no sense to me, either. You can talk about smallest resolvable details, but that does not imply little boxes with well defined boundaries at all. I don't think that is a good metaphor. Also, Planck units are generally considered only good to a constant factor, ...
by thoughtfully
Tue Feb 24, 2015 5:04 am UTC
Forum: Science
Topic: Spectrum of antimatter excursion
Replies: 11
Views: 2347

Re: Spectrum of antimatter excursion

Well, he did allow that some unobtainium shieldling would be necessary for the viewers. I hope the planet/ecosystem gets some as well, and the blast is directed out into space. 'Cause there's no kill like indiscriminate kill!
by thoughtfully
Mon Feb 23, 2015 8:37 pm UTC
Forum: Science
Topic: Spectrum of antimatter excursion
Replies: 11
Views: 2347

Re: Spectrum of antimatter excursion

Yakk wrote:There is some talk about using anti-protons to trigger fission.

Here's the nerd porn. Enjoy!
http://ffden-2.phys.uaf.edu/213.web.stu ... usion.html
http://ffden-2.phys.uaf.edu/213.web.stu ... usion.html
by thoughtfully
Mon Feb 23, 2015 7:31 pm UTC
Forum: Science
Topic: Spectrum of antimatter excursion
Replies: 11
Views: 2347

Re: Spectrum of antimatter excursion

It probably doesn't affect the considerations too much, but keep in mind that bulk, neutrally-charged antimatter is going to create a lot of pions when the nucleons annihilate. These eventually convert into gammas, but they travel some distance first. Probably not far, unless they are at the edge of...
by thoughtfully
Sun Feb 22, 2015 8:59 pm UTC
Forum: Science
Topic: Oxidisers
Replies: 30
Views: 7407

Re: Oxidisers

I'm not so sure about that. It's not a finite list if you can always add another monomer to the end of a polymer, or some other chain sort of molecule. It might not be especially useful as an oxidizer, but choosing a largest useful oxidizer is another one of those arbitrary choices.
by thoughtfully
Sun Feb 22, 2015 5:06 am UTC
Forum: Science
Topic: Sitting in an oven
Replies: 40
Views: 6774

Re: Sitting in an oven

A dry sauna wouldn't be dramatic enough for a sporting event. Vicarious risk of bodily harm does seem to be one of the main points of many sporting events.
by thoughtfully
Fri Feb 20, 2015 8:44 pm UTC
Forum: Science
Topic: Teleporting inside a wall
Replies: 16
Views: 5363

Re: Teleporting inside a wall

Details count. But it isn't magic if you can answer "how does that work". There will be an explosion if the two volumes are coerced into occupying the same space, from the same forces that normally hold them up against gravity. It could be a large and powerful explosion if the transfer hap...
by thoughtfully
Wed Feb 18, 2015 11:11 pm UTC
Forum: Science
Topic: Sitting in an oven
Replies: 40
Views: 6774

Re: Sitting in an oven

Steamy saunas are a totally different beast than dry ones, too. Steam is actually a damn good conductor of heat.
by thoughtfully
Sun Feb 08, 2015 11:25 pm UTC
Forum: Science
Topic: Motion mountain: crackpot?
Replies: 28
Views: 19060

Re: Motion mountain: crackpot?

Humans aren't the only biological lopsiders. The arrangement of internal organs is not symmetric (and isn't random: there's a preferred parity) in pretty much all tetrapod species, I believe, and probably large subsets of other taxa. Reaction to the mirror versions of some chemicals can vary quite a...
by thoughtfully
Sat Feb 07, 2015 8:17 pm UTC
Forum: Science
Topic: Human Gut Microbiome: Essential or Not?
Replies: 31
Views: 7088

Re: Human Gut Microbiome: Essential or Not?

Context is everything. Survival in what environment? Our livers are something like three times larger than necessary for modern affluent westerners (who don't have a drinking problem), but once upon a time, our diets were a lot more varied, and we didn't always have the luxury of getting our nutriti...
by thoughtfully
Fri Feb 06, 2015 12:59 pm UTC
Forum: Science
Topic: How long can we (human society) survive global warming?
Replies: 67
Views: 13475

Re: How long can we (human society) survive global warming?

Wanting a solution to pain is not the same as having a solution. Especially when short term pain gets the fix at the expense of long term pain. It could end up that the neglect of long term problems catches up to us sufficiently that we find ourselves in a long term period of survival-level existen...
by thoughtfully
Fri Feb 06, 2015 12:08 pm UTC
Forum: Science
Topic: How long can we (human society) survive global warming?
Replies: 67
Views: 13475

Re: How long can we (human society) survive global warming?

I think that living standards in the G20 will likely not fall. My cynicism says that rich nations aren't going to put themselves out to prevent living standards falling in poor countries though. Adapting isn't something that rich countries can "just do". It will be expensive. It will affe...
by thoughtfully
Thu Feb 05, 2015 5:06 pm UTC
Forum: Science
Topic: Matter or Antimatter--or does it matter?
Replies: 26
Views: 6167

Re: Matter or Antimatter--or does it matter?

What you're talking about is called a "naked singularity", and for some reason, it has given many physicists fits of existential dread. They even created a "cosmic censorship" hypothesis, to forbid such objects from disrupting the orderly universe described by General Relativity,...

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