Search found 22 matches

by elliptic
Mon Nov 14, 2016 4:06 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1759: "British Map"
Replies: 193
Views: 25037

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.
by elliptic
Fri Apr 01, 2016 10:57 am UTC
Forum: Science
Topic: Miscellaneous Science Questions
Replies: 2861
Views: 567788

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.
by elliptic
Mon Dec 14, 2015 1:45 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1616: "Lunch"
Replies: 71
Views: 14946

1616: "Lunch"

Image

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.
by elliptic
Wed Oct 28, 2015 5:29 pm UTC
Forum: Science
Topic: Silly Rotational Dynamics Question
Replies: 19
Views: 2950

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...
by elliptic
Wed May 06, 2015 1:52 pm UTC
Forum: Individual XKCD Comic Threads
Topic: 1521: “Sword in the Stone”
Replies: 96
Views: 15695

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...
by elliptic
Thu Mar 19, 2015 1:10 pm UTC
Forum: Mathematics
Topic: Probability.Addition rule,inclusive or,at least one of three
Replies: 4
Views: 1548

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 ......
by elliptic
Fri Feb 27, 2015 12:19 pm UTC
Forum: Mathematics
Topic: Combinatorics.Exclude when specific thing is before another.
Replies: 2
Views: 1157

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.
by elliptic
Fri Aug 01, 2014 1:23 pm UTC
Forum: Science
Topic: EMDrive and other reactionless propulsion claims
Replies: 71
Views: 13575

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*
by elliptic
Fri Jul 18, 2014 3:55 pm UTC
Forum: Science
Topic: Toffo Talks about Trains
Replies: 128
Views: 15613

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? ...
by elliptic
Thu Jun 19, 2014 4:10 pm UTC
Forum: Science
Topic: Mark McCutcheon's Final Theory of Everything
Replies: 154
Views: 26098

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...
by elliptic
Thu Jun 12, 2014 12:31 pm UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 2471

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 ...
by elliptic
Thu Jun 12, 2014 9:28 am UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 2471

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...
by elliptic
Tue Jun 10, 2014 12:14 pm UTC
Forum: Science
Topic: Locality of a Photon's Constituent Waves
Replies: 9
Views: 2471

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...
by elliptic
Thu May 01, 2014 9:52 am UTC
Forum: Science
Topic: Orbital coilgun accelerator
Replies: 38
Views: 4798

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...
by elliptic
Thu Feb 27, 2014 12:09 pm UTC
Forum: Science
Topic: pattern in electric field
Replies: 8
Views: 2645

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...
by elliptic
Tue Dec 03, 2013 2:51 pm UTC
Forum: Coding
Topic: [C++] Global variables in headers.
Replies: 13
Views: 8441

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...
by elliptic
Fri Nov 29, 2013 2:44 pm UTC
Forum: Coding
Topic: [C++] Global variables in headers.
Replies: 13
Views: 8441

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...
by elliptic
Mon Oct 14, 2013 10:50 am UTC
Forum: General
Topic: Are there any genuine bomb shelters around where you live?
Replies: 42
Views: 23711

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...
by elliptic
Fri Sep 13, 2013 2:51 pm UTC
Forum: Science
Topic: Pound v. Foot Pound
Replies: 101
Views: 22193

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...
by elliptic
Wed Jan 16, 2013 1:41 pm UTC
Forum: Science
Topic: Light in Closed Orbits?
Replies: 37
Views: 3742

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...
by elliptic
Wed Jan 16, 2013 1:33 pm UTC
Forum: Science
Topic: Alleged invisibility cloak
Replies: 33
Views: 6095

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 :D
by elliptic
Tue Aug 14, 2012 4:00 pm UTC
Forum: Science
Topic: Important Scientific Papers
Replies: 17
Views: 5907

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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