Search found 952 matches

by mfb
Mon May 05, 2014 7:48 pm UTC
Forum: Science
Topic: Orbital coilgun accelerator
Replies: 38
Views: 5972

Re: Orbital coilgun accelerator

Incidentally, the nature of the momentum exchange is such that even using the same bipropellant liquid rocket fuel on the coilgun station, you'd still only be using a fraction of the fuel. Around 70 tonnes (as opposed to the ~300 tonnes the rocket would need to use for itself). You would still have...
by mfb
Thu May 01, 2014 8:21 pm UTC
Forum: Mathematics
Topic: Distance to the moon
Replies: 5
Views: 2584

Re: Distance to the moon

I mean, dont you all want to know how far away the moon really is? 392934km . While it is certainly possible to do this today, it needs proper equipment as the moon is far away. In addition, it is a three-dimensional problem, so you cannot solve it graphically. And we have way better methods availa...
by mfb
Thu May 01, 2014 8:09 pm UTC
Forum: Science
Topic: Bremmstrahlung and gravity waves
Replies: 3
Views: 1374

Re: Bremmstrahlung and gravity waves

This is an open question - I don't find a reference that discusses both sides now, but I certainly saw that in the past. Probably yes. And there is no way to test it experimentally as long as we don't have a black hole. Here is a paper for radiation And here is a relation to Unruh radiation Edit: Ma...
by mfb
Thu May 01, 2014 8:00 pm UTC
Forum: Science
Topic: Green Lasers in a vacuum: Visible indirectly?
Replies: 13
Views: 4720

Re: Green Lasers in a vacuum: Visible indirectly?

A simpler addition - if you aren't in some kind of "clean-room", there is *always* some dust floating around, and if your pointer is powerful enough, this will make the beam visible almost anywhere (in-atmosphere). Even in a clean-room, there is dust floating around. The differences are j...
by mfb
Thu May 01, 2014 7:57 pm UTC
Forum: Science
Topic: Return of the LHC
Replies: 7
Views: 2188

Re: Return of the LHC

All relevant interpretations are within the standard model - tetraquark, meson molecule, some weird QCD stuff - there is no reason to expect physics beyond the standard model here. It is just a result* of the standard model we did not see before. *it is not even a part of the standard model, as it i...
by mfb
Thu May 01, 2014 7:29 pm UTC
Forum: Science
Topic: Energy requirements to launch to LEO (from vacuum zeppelin)
Replies: 46
Views: 36942

Re: Energy requirements to launch to LEO (from vacuum zeppel

You would still have to re-accelerate the capturing mechanism afterwards. The only thing you can get is more time - and therefore access to more efficient engines like ion engines. In terms of total energy spent, it could be even worse if your deceleration mechanism (in terms of relative velocity) d...
by mfb
Thu May 01, 2014 7:06 pm UTC
Forum: Science
Topic: Orbital coilgun accelerator
Replies: 38
Views: 5972

Re: Orbital coilgun accelerator

Incidentally, the nature of the momentum exchange is such that even using the same bipropellant liquid rocket fuel on the coilgun station, you'd still only be using a fraction of the fuel. Around 70 tonnes (as opposed to the ~300 tonnes the rocket would need to use for itself). You would still have...
by mfb
Sat Mar 15, 2014 4:11 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1342: "Ancient Stars"
Replies: 76
Views: 18100

Re: 1342: "Ancient Stars"

Taking the 1400 systems within 50 LY figure and extrapolating up to 1000 LY, that gives 8000 times as many systems, or about 10 000 000 stars. So the million brightest (by apparent magnitude) stars in the sky are probably mostly within 1000 LY - on the other hand, if you can see over a million diff...
by mfb
Fri Feb 28, 2014 7:11 pm UTC
Forum: Science
Topic: Could Neutrinos be Gravitons?
Replies: 37
Views: 7909

Re: Could Neutrinos be Gravitons?

Ok there was faulty wiring but all of the results afterwards concluded that neutrinos goes the same speed as light which is interesting that a particle with mass can go as fast as a particle with out mass. So the warp theory could still be relevant. The expected speed difference to light is so extr...
by mfb
Fri Feb 28, 2014 6:53 pm UTC
Forum: News & Articles
Topic: The Thread To Remind Me We're Living In The Future
Replies: 1943
Views: 411510

Re: The Thread To Remind Me We're Living In The Future

Is there any way to tell from arXiv if a paper has been excepted for publication? Sometimes it is written under "comments". I don't think Hawking will get problems publishing anything he writes. http://arstechnica.com/science/2014/02/giant-leap-for-nuclear-fusion-as-scientists-get-more-en...
by mfb
Tue Dec 03, 2013 8:54 pm UTC
Forum: Science
Topic: What is the smallest object that has gravity?
Replies: 65
Views: 19591

Re: What is the smallest object that has gravity?

Well, the concept of measuring a particular force is more easily conceptualized if we think about what weight would or wouldn't affect instrumentation. Hence the eyebrow hair example. I'm guessing a small grain of sand is in the same ballpark. Anything around 10 -7 grams will work, and it's not ter...
by mfb
Tue Dec 03, 2013 6:23 pm UTC
Forum: Science
Topic: What is the smallest object that has gravity?
Replies: 65
Views: 19591

Re: What is the smallest object that has gravity?

Cool story! I wouldn't have expected that to work, because of the (assumedly) large distance, but apparantely it does... Well, let's see here. Rough estimate of a garbage truck's mass -- 15 tonnes. Rough estimate of the distance -- 10 meters. Rough estimate of the test mass -- 10 kg. By the power o...
by mfb
Tue Dec 03, 2013 6:18 pm UTC
Forum: What If?
Topic: What-If 0074: "Soda Planet"
Replies: 41
Views: 20312

Re: What-If 0074: "Soda Planet"

Humans drink 7% of all water ever consumed by all humans as carbonated beverages each year? That can not be right. I mean yes, population growth is exponential, and a significant fraction of all humans who ever lived are alive right now. About 7% in fact. But that would still require carbonated bev...
by mfb
Mon Dec 02, 2013 11:26 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1298: "It's a beautiful day in the neighborhood!"
Replies: 71
Views: 18287

Re: 1298: "It's a beautiful day in the neighborhood!"

Anyway, I vote for graphics fail, because it's not crystal-clear that the planets are represented in diameter scale. What if the discs represent volume? That would make more sense, since the gravitational force, and thus habitability, depends more on volume than diameter. But then we'd need a densi...
by mfb
Mon Nov 11, 2013 9:21 pm UTC
Forum: Science
Topic: Creationism and the kinetic energy of impact events
Replies: 19
Views: 3954

Re: Creationism and the kinetic energy of impact events

Looking at the numbers calculated so far, I don't think that works. Why not compare moon and earth? I don't see any reason why moon should have gotten so many asteroids if earth did not. So where are all the craters on earth? The large ones are not influenced by the atmosphere and several craters ha...
by mfb
Mon Nov 11, 2013 9:01 pm UTC
Forum: Science
Topic: What is the smallest object that has gravity?
Replies: 65
Views: 19591

Re: What is the smallest object that has gravity?

FancyHat wrote:If you've got a uniform, spherical mass of, say, 10kg, the acceleration due to its gravity at a distance of 0.1 m from its centre will be 66.74 nm/s2.
It is fascinating that this acceleration is easy to measure today - in real-time.
by mfb
Sun Oct 27, 2013 8:06 pm UTC
Forum: Mathematics
Topic: Sum of Independent Variables = Uniform?
Replies: 7
Views: 2417

Re: Sum of Independent Variables = Uniform?

Qaanol wrote:There is no such precursor to a uniform distribution in Euclidean space.
I wonder if there is a general description of the distributions that have such a thing.
by mfb
Thu Oct 24, 2013 10:50 pm UTC
Forum: Mathematics
Topic: Order of magnitude of mathematical knowledge?
Replies: 3
Views: 2187

Re: Order of magnitude of mathematical knowledge?

So, in sum, a newly minted PhD probably knows about 1% of all there is to know in mathematics. I'd say this is probably a close to the upper bound, since 1 paper a day is fairly ambitious, and I assumed rather arbitrarily that 90% of papers have no novel content. Not so far away from this comic . I...
by mfb
Thu Oct 24, 2013 10:42 pm UTC
Forum: Mathematics
Topic: Sum of Independent Variables = Uniform?
Replies: 7
Views: 2417

Re: Sum of Independent Variables = Uniform?

Nicias: Is that a proof of the existence? If it exists, it has to be symmetric, limited to a finite interval, and I think as it approaches the borders of those interval the probability distribution has to scale with 1/sqrt(x) where x is the distance to the border (in more mathematical terms: f(x)*sq...
by mfb
Thu Oct 24, 2013 10:03 pm UTC
Forum: Science
Topic: Magnitude of celestial body bright enough to cast shadow
Replies: 12
Views: 5863

Re: Magnitude of celestial body bright enough to cast shadow

"Cast a shadow" is pretty vague: with sensitive enough instruments, you could measure the shadows cast by every star individually. In order to answer this, you'd need to define what shadows do and don't count. My personal definition would be that a light source can cast a shadow if it is ...
by mfb
Mon Oct 14, 2013 7:08 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1276: "Angular Size"
Replies: 98
Views: 27241

Re: 1276: "Angular Size"

A question for the physicists: Is the angular size proportional to the gravitational pull of the object? Another way to answer this: For spherical objects of the same angular size, gravitational pull is proportional to the diameter of the object multiplied by the density - but density is usually so...
by mfb
Fri Oct 11, 2013 5:22 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1276: "Angular Size"
Replies: 98
Views: 27241

Re: 1276: "Angular Size"

So: the e.coli plays ping-pong during football games? I don't get it (this angular size thing). :( As seen from the center of earth, Ganymede would look as large as 1/2 of a soccer field on the surface of earth. Angular size refers to the apparent diameter of an object, not its area. So I'd expect ...
by mfb
Sun Oct 06, 2013 3:08 pm UTC
Forum: Science
Topic: [Physics] Simplified version of Afshar's experiment
Replies: 2
Views: 1757

Re: [Physics] Simplified version of Afshar's experiment

https://en.wikipedia.org/wiki/Afshar_experiment If you detect the position of light at the place of the grid, you don't get which-way-information, and the detectors behind the lens will see point-like sources at your detectors. If you detect the direction of light (but not the position), you get whi...
by mfb
Mon Sep 23, 2013 5:29 pm UTC
Forum: Science
Topic: Putting elements in a super collider. How?
Replies: 10
Views: 4321

Re: Putting elements in a super collider. How?

This is the source of all protons in the LHC: http://vixra.files.wordpress.com/2011/05/proton-source.jpg?w=450 Image source Small packets of hydrogen are ionized, and ionized hydrogen is just protons and electrons. The element to be bombarded is not a single atom, but a specially prepared block of t...
by mfb
Wed Sep 18, 2013 7:34 pm UTC
Forum: What If?
Topic: What-If 0063: "Google's Datacenters on Punch Cards"
Replies: 58
Views: 21240

Re: What-If 0063: "Google's Datacenters on Punch Cards"

CERN seems to be around 100 PB themselves... So smashing stuff around does also produce lot of data ;D http://home.web.cern.ch/about/updates/2013/02/cern-data-centre-passes-100-petabytes It would be way more if the experiments would not throw away most of the data (the collisions which are not so i...
by mfb
Sat Aug 31, 2013 2:57 pm UTC
Forum: What If?
Topic: What-if 0060: "Signs of Life"
Replies: 71
Views: 41020

Re: What-if 0060: "Signs of Life"

The linked random point generator gives an error:
509 Bandwidth Limit Exceeded
The server is temporarily unable to service your request due to the site owner reaching his/her bandwidth limit. Please try again later.
I wonder which effect could have increased the traffic... :D.
by mfb
Fri Aug 30, 2013 4:20 pm UTC
Forum: What If?
Topic: What-if 0060: "Signs of Life"
Replies: 71
Views: 41020

Re: What-if 0060: "Signs of Life"

I wonder what uncontacted tribes or even contacted hunter-gatherer tribes think of satellites. Surely they've noticed them, and that they didn't exist in the relatively recent past. Do missionaries explain it to them? Do they understand through the language barrier? Airplanes are much more mysterio...
by mfb
Tue Aug 27, 2013 5:19 pm UTC
Forum: What If?
Topic: What-if 0060: "Signs of Life"
Replies: 71
Views: 41020

Re: What-if 0060: "Signs of Life"

chris857 wrote:
Wait for nightfall.[4] (And then go crazy and burn down your civilization when you see the stars for the first time.)


Asimov reference for the win.

Thanks. I did not remember book title (Nightfall) and author, and I was sure someone else would :D.
by mfb
Fri Aug 02, 2013 5:02 pm UTC
Forum: Science
Topic: How did we figure out the Earth's mass?
Replies: 28
Views: 10733

Re: How did we figure out the Earth's mass?

Eratosthenes experiment is pretty trivial to do. If you're on a new planet, exploring and mapping your new environs is going to be a pretty high priority. Once you've mapped a few hundred miles and computed latitudes, you're done. I wonder what the most unexpected possible sight would be if you wer...
by mfb
Wed Jul 03, 2013 9:35 pm UTC
Forum: Science
Topic: An altrenative rocket technology idea
Replies: 24
Views: 10854

Re: An altrenative rocket technology idea

I saw that as a serious proposal somewhere, but the conclusions were not very optimistic.
It was a bit better with a solid hull, as you can get a higher air pressure then.

Anyway, 50km is very short for orbital launches - you need an extreme acceleration, or you get a very low velocity as result.
by mfb
Wed Jul 03, 2013 9:12 pm UTC
Forum: Mathematics
Topic: Clever High School Math Problems
Replies: 31
Views: 14108

Re: Clever High School Math Problems

That puzzle can be extended to other bases, with other nice solutions. The base has to be even, otherwise there is no solution It would be interesting to see if there is a solution for a base larger than 14 (there is one with 14). I wrote a hack to search for solutions, but that is not quick enough ...
by mfb
Wed May 01, 2013 11:21 pm UTC
Forum: Science
Topic: Gravitational mass of an electron?
Replies: 35
Views: 12018

Re: Gravitational mass of an electron?

because AFAIK the only 2 data points we have are "neutrons" and "electron-proton pairs" Those are very good data points, however. Neutrons and protons are very similar, they both gain most of their energy from QCD binding energy and some small fraction (still larger than the ele...
by mfb
Wed May 01, 2013 11:10 pm UTC
Forum: Science
Topic: Reality Sharing aka Lifecasting Extreme
Replies: 15
Views: 2292

Re: Reality Sharing aka Lifecasting Extreme

You could start with audio and video. Those can be captured and replayed externally, even with current technology. Motion sickness would be a serious issue for the visual inputs (but see below). Taste and smell might be possible to record and reproduce externally at some point in the future. A reali...
by mfb
Sun Apr 28, 2013 11:25 am UTC
Forum: Science
Topic: Angular Momentum - Webcomic 162
Replies: 8
Views: 3518

Re: Angular Momentum - Webcomic 162

Link to the comic
You are right, she has to spin in the opposite direction on the southern hemisphere.
by mfb
Sat Mar 30, 2013 9:40 pm UTC
Forum: Mathematics
Topic: New Rule about jsMath
Replies: 9
Views: 14206

Re: New Rule about jsMath

Did you consider MathJax? It is quick enough to handle 10-50 formulas per page without notable delays (assuming a reasonable length, don't write 10+ pages in LaTeX).
by mfb
Sat Mar 30, 2013 9:34 pm UTC
Forum: Science
Topic: Is there any way to overcome the expansion of the universe?
Replies: 5
Views: 2181

Re: be there ænig way to overcome the expansion of the unive

Question 1: would it be even remotely plausible for an wormhole to link two galaxies? Speculative, probably not with current physics, but it ca n not be fully ruled out. Question 2: They say that eventually the galaxies woll be far enough apart that billions of years from now future astronomers, if...
by mfb
Wed Mar 27, 2013 9:08 pm UTC
Forum: What If?
Topic: What-If 0038: "Voyager"
Replies: 39
Views: 15989

Re: What-If 0038: "Voyager"

Unless they pointed it to something (I don't know) then it is overwhelmingly likely that it will never reach another star system, and then exit the galaxy and never enter another galaxy. At least, that's what I heard. It is way too slow to escape from our galaxy, unless it gets a really close fly-b...
by mfb
Mon Feb 25, 2013 8:51 pm UTC
Forum: Science
Topic: Asteroid redirection question
Replies: 22
Views: 3976

Re: Asteroid redirection question

Similar-sized object? M_spacecraft << M_asteroid Let's consider a real example: M=10000 tons, deflection time 2 years, warning time (minus time for the satellite to reach the asteroid) 6 years. Required velocity change for the asteroid: 10000km in 5 years or 6cm/s M_spacecraft = 15 tons, distance d=...
by mfb
Wed Feb 06, 2013 8:31 pm UTC
Forum: Mathematics
Topic: function powers for identity function
Replies: 11
Views: 3232

Re: function powers for identity function

An "easy" way of calculating a f n (x)=x for any x would be to take a nth primitive root of 1*, call it p and set f(x)=x*p. *Here primitive root means that p n =1 but no p m =1 for any m<n. For example, a 2nd primitive root of 1 is -1, since -1 2 =1 but -1 1 =/=1. In the real numbers, thi...
by mfb
Mon Jan 28, 2013 2:46 pm UTC
Forum: What If?
Topic: What-If 0029: "Spent Fuel Pool"
Replies: 167
Views: 47270

Re: What-If 0029: Spent Fuel Pool

It wasn't all that long ago that scientists were sure that stones never fell from the sky. They attributed eyewitnesses who claimed to see stones fall from the sky as liars or victims of mass hallucination. Thomas Jefferson interviewed a collection of reputable people who claimed to see a meteor, a...

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