## Search found 33 matches

Thu Dec 06, 2018 11:38 am UTC
Forum: Individual XKCD Comic Threads
Topic: 2081: Middle Latitudes
Replies: 27
Views: 5849

### Re: 2081: Middle Latitudes

I'm going to be remarkably pedantic and point out the second of those "Summer, northern England" pictures (looking across Buttermere in the Lake District) is actually late winter or very early spring, going by the angle of the sun and the state of the vegetation. For bonus points it's only...
Mon Aug 07, 2017 9:30 am UTC
Forum: Mathematics
Topic: Foolish question debunked. Move on, nothing to see.
Replies: 80
Views: 14713

### Re: Does the Banach–Tarski Paradox prove that you can't see the edge of the universe?

So place an observer in space so we can see him, somewhere close to the edge of the observable Universe. What can he see? Now if we place another observer where the third can see the second. What can he see? Each of these locations is a set with intersections with other sets. All you're saying is t...
Fri Jun 09, 2017 1:33 pm UTC
Forum: News & Articles
Topic: British Snap Election - Theresa, Meh; Corbyn near-win; So long, Farron, auf wiedersehen goodbyeee
Replies: 127
Views: 38391

### Re: British Snap Election - not a re-referendum?

That plus things just tend to happen quickly after UK elections. The idea of a several-week-long interregnum whilst the dust settles and the parties talk things over would be anathema, even without the upcoming Brexit negotiations looming over everything. In 2010 it took five days flat for the Torie...
Tue Apr 04, 2017 11:19 am UTC
Forum: Mathematics
Topic: Induction Question
Replies: 8
Views: 3629

### Re: Induction Question

To put it in more specific terms... 2^(k+1) = 2 * 2 * ... * 2 = the product of k+1 2s. 2^(k+1) + 2^(k+1) = 2 * 2^(k+1) = the product of... how many 2s? Also... You can re-express the formula as 1 + 2^0 + 2^1 + ... + 2^n = 2^n+1. So what you're proving is that, given a binary number comprising al...
Fri Feb 17, 2017 3:39 pm UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2958
Views: 719878

### Re: RELATIVITY QUESTIONS! (and other common queries)

You're not the first person to spot that: https://xkcd.com/895/
Thu Feb 16, 2017 11:42 am UTC
Forum: Logic Puzzles
Topic: Escape the Frictionless Circle
Replies: 156
Views: 67027

### Re: Escape the Frictionless Circle

More: As stated, when the rope is spilled out by 40m, you negate any spin momentum by spinning on the spot, moving the rope end from hand to hand. The momentum at the other end is the spin in the block and the directional momentum from where you pushed it. Consider now that the energy on you is a z...
Wed Feb 15, 2017 11:17 am UTC
Forum: Logic Puzzles
Topic: Escape the Frictionless Circle
Replies: 156
Views: 67027

### Re: Escape the Frictionless Circle

More Info: You negate the spin by turning yourself. You keep turning on the spot, but the gold continues to unravel the rope. You have to keep passing the rope around you as you slowly drift, following the gold block. Momentum still exists in you turning on the spot, that momentum is simply NOT app...
Mon Feb 13, 2017 12:58 pm UTC
Forum: Logic Puzzles
Topic: Escape the Frictionless Circle
Replies: 156
Views: 67027

### Re: Escape the Frictionless Circle

I'm not sure I've completely followed all of that. But whatever you're trying to do, it blatantly breaks conservation of momentum so it can't work, sorry.
Tue Jan 17, 2017 3:52 pm UTC
Forum: News & Articles
Topic: British EU referendum in June [update: Leave wins 52% - 48%, politics ensue]
Replies: 1475
Views: 253940

### Re: British EU referendum in June [update: Leave wins 52% - 48%, politics ensue]

The exact question on the ballot was: "Should the United Kingdom remain a member of the European Union or leave the European Union?"

Which you presumably know already, given your location. Anyway, no-one else in the UK seemed to have any difficulty parsing it.
Fri Jan 13, 2017 12:44 pm UTC
Forum: Science
Topic: Can you (passively) heat an object hotter than your source?
Replies: 98
Views: 26297

### Re: Can you (passively) heat an object hotter than your source?

Its just an old "paradox" to which the answer is the thermal radiation from each sphere is not radial, it's in all directions from each point on the surface, so it doesn't refocus onto the other one.
Mon Dec 19, 2016 4:35 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1774: "Adjective Foods"
Replies: 64
Views: 12363

### Re: 1774: "Adjective Foods"

Do US regulations make the same distinction between flavo[u]r and flavo[u]red as the UK? What distinction does the UK make? "Flavoured" => real ingredients "Flavour" => synthetic flavouring Eg. "strawberry flavoured yoghurt" has actual strawberries in it, but "str...
Mon Nov 14, 2016 4:06 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1759: "British Map"
Replies: 193
Views: 40330

### Re: 1759: "British Map"

I'm a little disappointed that Cadbury isn't located just south of Birmingham

It's actually just north of Exeter.

...and about 60km west of both North Cadbury and South Cadbury.

Cardigan is a real place, as well.
Fri Apr 01, 2016 10:57 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2958
Views: 719878

### Re: RELATIVITY QUESTIONS! (and other common queries)

Err... an instantaneous transporter *is* FTL travel...

And "instantaneous" transport in one reference frame can always be backwards-in-time in another. Thats the whole point.
Mon Dec 14, 2015 1:45 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1616: "Lunch"
Replies: 71
Views: 17858

### 1616: "Lunch"

Title text: "I'm trying to be healthier, so after I eat this brick of cheese, I'll have a spoonful of grease-soaked vegetables."

Sounds better with a glass of water, a handful of barley and a thimble of raw alcohol, though.
Wed Oct 28, 2015 5:29 pm UTC
Forum: Science
Topic: Silly Rotational Dynamics Question
Replies: 19
Views: 3458

### Re: Silly Rotational Dynamics Question

But even in the absence of friction, a force is still being exerted on the object by the edge of the track. To clarify further: energy = force x distance moved *in the direction of the force*. For an object held in a circular orbit (which is what we're talking about) the force towards the centre is...
Wed May 06, 2015 1:52 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1521: “Sword in the Stone”
Replies: 96
Views: 20573

### Re: 1521: “Sword in the Stone”

According to Wikipedia, it sounds like they deliberately misspelled it to "lede" to differentiate it from the metal "lead" which was used in typesetting. And in a curiously second-order sub-textual reference, I give you a 70s rock group with a penchant for pseudo-medieval mythol...
Thu Mar 19, 2015 1:10 pm UTC
Forum: Mathematics
Topic: Probability.Addition rule,inclusive or,at least one of three
Replies: 4
Views: 1917

### Re: Probability.Addition rule,inclusive or,at least one of t

With questions like this the trick is to turn it the other way around.

What's the probability that the student passes *none* of the exams?

Then the probability of any other result (ie. at least one pass) is ......
Fri Feb 27, 2015 12:19 pm UTC
Forum: Mathematics
Topic: Combinatorics.Exclude when specific thing is before another.
Replies: 2
Views: 1389

### Re: Combinatorics.Exclude when specific thing is before anot

Total number of speaker orderings N(total) = 5! = 120.

By symmetry, N(Jack before John) = N(John before Jack).

Therefore, N(John before Jack) = N(total) / 2 = 60.
Fri Aug 01, 2014 1:23 pm UTC
Forum: Science
Topic: EMDrive and other reactionless propulsion claims
Replies: 71
Views: 16570

### Re: NASA scientists report positively on propellant-less dri

Nowhere in that "paper" does he consider an equal and opposing force on the tapered walls of the waveguide.

*sigh*
Fri Jul 18, 2014 3:55 pm UTC
Forum: Science
Topic: Toffo Talks about Trains
Replies: 128
Views: 19031

### Re: Toffo Talks about Trains

All these questions are just variants on the barn/pole paradox, shirley. In motion the pole is shorter then the barn due to length contraction. Shut both doors to trap it and when it comes to rest it still fits, because now it's under compression. And where does the energy to compress it come from? ...
Thu Jun 19, 2014 4:10 pm UTC
Forum: Science
Topic: Mark McCutcheon's Final Theory of Everything
Replies: 154
Views: 31561

### Re: Wrong on the Internet: The Final Theory

Our future as a species depends upon our understanding that the search for the truth is an ongoing process. And success in that search depends on critically assessing novel ideas and throwing them out ruthlessly if they don't stand up to reality. McCutcheon's don't stand up at even the most basic l...
Thu Jun 12, 2014 12:31 pm UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 3097

### Re: Locality of a Photon's Constituent Waves

...the wavefunction evolves according to the appropriate wave equation (Schrodinger's equation in non-relativistic QM) which gives nice smoothly evolving waves spreading out, interfering with each other and bouncing off the environment: very much like normal ripples in a pond. Out of curiosity: at ...
Thu Jun 12, 2014 9:28 am UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 3097

### Re: Locality of a Photon's Constituent Waves

I get the feeling that it's a difference in that the wavefunctions are, in my mind, modeling tools for our understanding of reality, while it objectively is something completely different. What this "completele different" might be, I have no idea ... I just get the feeling that the wave p...
Tue Jun 10, 2014 12:14 pm UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 3097

### Re: Locality of a Photon's Constituent Waves

But is it, or is it more of a can be explained as ? Why do you think there's a difference? The behaviour of particles such as photons can be explained using quantum theory, in which the particle is represented by a wavefunction. I'm struggling with the notion that a wavefunction should instantly oc...
Thu May 01, 2014 9:52 am UTC
Forum: Science
Topic: Orbital coilgun accelerator
Replies: 38
Views: 5854

### Re: Orbital coilgun accelerator

The launch trajectory will be designed to intersect the orbital path of the space-station-tube. High-speed computers will determine the exact trajectory of both spacecraft and line them up such that the tube catches up to the rocket and passes around it from back to front. This part also seems, err...
Thu Feb 27, 2014 12:09 pm UTC
Forum: Science
Topic: pattern in electric field
Replies: 8
Views: 3059

### Re: pattern in electric field

angle of the charge? Electric charge is scalar so doesn't have any direction or angle. But the electric *field* at each point is a vector... Presumably he was calculating field strength at each point with a vector sum over the effect of all the charges, and getting the "direction" part of...
Tue Dec 03, 2013 2:51 pm UTC
Forum: Coding
Topic: [C++] Global variables in headers.
Replies: 13
Views: 10233

### Re: [C++] Global variables in headers.

The main issue I have is that I don't see why this problem exists in the first place. It seems a weird language limitation. I can think of no reason why defining things in a header would be effectively illegal. Because a C/C++ header isn't processed independently in the build, it's just an easy way...
Fri Nov 29, 2013 2:44 pm UTC
Forum: Coding
Topic: [C++] Global variables in headers.
Replies: 13
Views: 10233

### Re: [C++] Global variables in headers.

What Ubik said. A header file is not a place for defining stuff, it's for declaring stuff. Pick a source file and define your variable there at file scope. Declare it as "extern" in the common header (or individually in the other source files). It doesn't matter that there's no single entr...
Mon Oct 14, 2013 10:50 am UTC
Forum: General
Topic: Are there any genuine bomb shelters around where you live?
Replies: 42
Views: 26213

### Re: Are there any genuine bomb shelters around where you liv

Not bomb shelters as such but plenty of WW2 pillboxes (brick/concrete machine-gun bunkers) still standing in the fields and dug into hedgerows around where I live in Somerset in the UK. All built in 1940 for the GHQ Stop Line Red, which was supposed to be the last fixed line of defence if the Battle...
Fri Sep 13, 2013 2:51 pm UTC
Forum: Science
Topic: Pound v. Foot Pound
Replies: 101
Views: 24419

### Re: Pound v. Foot Pound

No, sine of radians and sine of degrees are not the same sine functions. And in other news, log e and log 10 are not the same log functions. But they are both log functions, and when I see a bare log() my head doesn't asplode: I just have to deduce what the base is supposed to be. In a mathematical...
Wed Jan 16, 2013 1:41 pm UTC
Forum: Science
Topic: Light in Closed Orbits?
Replies: 37
Views: 4499

### Re: Light in Closed Orbits?

The stable orbit for light round a non-rotating black hole is at 1.5 times the Schwarzschild radius.

As always it gets more complicated with a rotating BH...
Wed Jan 16, 2013 1:33 pm UTC
Forum: Science
Topic: Alleged invisibility cloak
Replies: 33
Views: 6997

### Re: Alleged invisibility cloak

If there is a layer of dirt or dust on top of the cloak, I have to assume that the enemy is going to see that layer of dirt or dust.

And even if the cloak starts off clean the natural enemy countermeasure is... a paintball gun
Tue Aug 14, 2012 4:00 pm UTC
Forum: Science
Topic: Important Scientific Papers
Replies: 17
Views: 6919

### Re: Important Scientific Papers

On a different note (and in the field of engineering rather than pure science) how about Claude Shannon's "Communication in the presence of noise", which underpins all modern digital communications technology (including of course the interwebz from which you'll be downloading it). Aside fr...

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