explain xkcd - User contributions [en]

Talk:1938: Meltdown and Spectre

2018-01-06T11:39:21Z

162.158.34.4: Clarification as to a trolley for the benefit of overseas readers

The "trolley problem" is the ethical dilemma thought experiment where an out-of-control trolley is heading to a junction (which you have control over) - to one side it'll kill one group of people - to the other, some others. Your moral dilemma is deciding which is the "best" outcome (eg, hitting a dozen five year old children or three Nobel laureats). This is like a software "if" statement. Speculative execution in most CPU chips is where the computer always takes both sides of a decision like this - explores what will happen down each path - and only causes the effects of the decision to happen when the decision as to which way to proceed is decided. This allows it to keep on doing useful work while some slower decision is made. The "quantum" aspect of this is that in some versions of quantum theory, quantum-level particles take every possible path at once and the result is the sum of all of them.

In a sense, the computer is exploring the consequences of the trolley problem in a quantum-like manner.

This would all be OK if it were not for the fact that devious black-hat hackers can come up with devious ways to see the information that should have been discarded in the "path-not-taken". So even though the computer will eventually decide that some piece of information should not be accessible - you can find out the value it would hypothetically read - even though it will soon decide that it should not access the information.

The "rowhammer" problem is something entirely different. Computer memories are organized as a two-dimensional grid of rows and columns - and are physically constructed from tiny capacitors. If you apply just the RIGHT pattern of rapid changes to one row of the grid, you can cause one of the capacitors on the next row to incorrectly change state. This is a design flaw in the memory chip - and it allows (in some circumstances) programs to change data in memory locations that they have no right to change.

[[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 19:33, 5 January 2018 (UTC)

uhhh did you just copy and paste your entire edit into talk? [[User:DPS2004|DPS2004'); DROP TABLE users;--]] ([[User talk:DPS2004|talk]]) 20:19, 5 January 2018 (UTC)

: Pretty much. When I got here, there was no information about the comic at all. Since I'm unfamiliar with all of the other stuff that goes into an explain, I left it as a comment so someone else could use it...but after a while, nobody did, so I copy-pasted it into the explanation...with some tweaks! Sorry if that was a faux-pas of some variety! [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 21:53, 5 January 2018 (UTC)

What? Servers are vulnerable to actual hammers? Huh, do you suppose they're be vulnerable to an actual trolley as well? I have a spare server, does anyone have a spare trolley? ~~ SiliconWolf

: My server is actually mounted inside a trolley - precisely to avoid this kind of issue. [[User:SteveBaker|SteveBaker]] ([[User talk:SteveBaker|talk]]) 23:02, 5 January 2018 (UTC)

:I wouldn't recommend that. A collision would anger the honeybees. [[User talk:AgentMuffin|~AgentMuffin]]

The most helpful technical explanation I’ve found is here: https://www.raspberrypi.org/blog/why-raspberry-pi-isnt-vulnerable-to-spectre-or-meltdown/ ;the comments also provide useful clarification. [[User:PotatoGod|PotatoGod]] ([[User talk:PotatoGod|talk]]) 02:54, 6 January 2018 (UTC)

Could an explanation be added as to what a trolley is? Being in the UK, my first thought was that of a shopping trolley (US: Shopping cart). Over here, we call trollies "trams" [[Special:Contributions/162.158.34.4|162.158.34.4]] 11:39, 6 January 2018 (UTC)

Talk:1924: Solar Panels

2017-12-06T09:10:23Z

162.158.34.4:

Sorry, but who, except the odd American, has *empty space* next to anything that belongs to him? ;-) --[[Special:Contributions/162.158.89.199|162.158.89.199]] 20:47, 4 December 2017 (UTC)

And really, if it moves, just keep the diesel engine in it, or switch to hybrid if you can. Batteries that are charged from power plants running on fossile fuel are an ecological nightmare. And car batteries are usually charged overnight, when solar panels are dead. --[[Special:Contributions/162.158.89.199|162.158.89.199]] 20:54, 4 December 2017 (UTC)

:You are right that charging batteries from power plants running on fossile fuel doesn't really bring any ecological advantages ... assuming the engine operates close to optimal parameters. Most cars doesn't operate near optimal parameters inside city, but do on highways, hence hybrid. Also, it is much more ecological to have batteries charged by nuclear power plants. -- [[User:Hkmaly|Hkmaly]] ([[User talk:Hkmaly|talk]]) 04:15, 5 December 2017 (UTC)
::Ja, Germany here. Our whole politics from left to right has this obsessive-compulsive nuclear-power-blows-up-and-poisons-everyone problem, so we're switching them off. --[[Special:Contributions/162.158.89.133|162.158.89.133]] 07:49, 6 December 2017 (UTC)
: I always thought of the main advantage of electrical battery powered cars (instead of petrol or Diesel powered ones) was not so much the immediate ecological improvement, but rather that (once they are the norm) you don't need to convince EVERY SINGLE CAR USER to get rid of their old car and get a new one (Like you have to do now, when you invent engines which use less fuel or something). Instead, when you change the overall energy production of a country (hopefully to something more sustainable and envronmentally friendly), the cars will just passively follow. [[Special:Contributions/162.158.89.37|162.158.89.37]] 14:46, 5 December 2017 (UTC)
:: I think the main motivation for moving to electric vehicles is that it largely moves the pollution away from where people are. (From the energy production, anyway - particulate pollution from brakes, tyres, etc. is a whole other matter...)[[Special:Contributions/162.158.34.4|162.158.34.4]] 09:10, 6 December 2017 (UTC)

I think that the reference to solar panels on roads in the title text could also be talking about the disaster that is solar roadways.
[[Special:Contributions/108.162.221.244|108.162.221.244]] 22:50, 4 December 2017 (UTC)

I don't think it's appropriate to use rooftops as an example of where solar panels should not go when the title text of the comic specifically uses rooftops as an example of a good place for solar panels. How many people have an empty field near their house? I also think it's worth mentioning [https://en.wikipedia.org/wiki/Smart_highway#Photovoltaic_pavement Solar Freakin' Roadways] [[User:YM Industries|YM Industries]] ([[User talk:YM Industries|talk]]) 04:08, 5 December 2017 (UTC)

: I agree, rooftops are kinda the prime example for good places to put solar panels. Especially because even in small cities, there are tons of flat-roofed buildings (which would make the alignment to the sun possible) and it is often (nearly) unused space, whereas an "empty" (as in not-build-upon) space could be used for lots of other things, not least just some wild nature. I went ahead and changed the explanation accordingly, putting hte emphasis mor on inclined vs. flat surfaces (and this free to select optimal direction)[[Special:Contributions/162.158.89.37|162.158.89.37]] 14:46, 5 December 2017 (UTC)

The current transcript is not very useful for people who use screen readers, or for any other purpose (e.g. full text search). Could someone please describe the flowchart in a purely textual, "linear" fashion, as was done for other flowchart comics? Thanks very much in advance! Zetfr 15:01, 5 December 2017 (UTC)
:I tried to improve it, hopefully it's helpful. [[User:Asdf|Asdf]] ([[User talk:Asdf|talk]]) 18:02, 5 December 2017 (UTC)
::Great, thanks a lot! Zetfr 22:06, 5 December 2017 (UTC)

The flowchart doesn't use standard flowchart symbols - they remind me of cars/trucks, each having a (rounded body) plus two wheels (holding yes and no). Anyone think this is deliberate?
:Not particularly as he used similar design in [[1688: Map Age Guide]]. --[[User:Kynde|Kynde]] ([[User talk:Kynde|talk]]) 09:01, 6 December 2017 (UTC)

The reason that you don't want to put solar panels on something that is hot is not because hot things use more power. It's because the efficiency of solar panels decreases as a function of temperature: See here for example http://news.energysage.com/solar-panel-temperature-overheating/ . This is why solar panels on a road are not a great idea (among other reasons). [[Special:Contributions/108.162.219.76|108.162.219.76]] 01:23, 6 December 2017 (UTC)

1922: Interferometry

2017-11-29T16:34:07Z

162.158.34.4: /* Explanation */ Added explanation of astronomical interferometry and title text

{{comic
| number = 1922
| date = November 29, 2017
| title = Interferometry
| image = interferometry.png
| titletext = It's important to note that while the effective size of the dog can be arbitrarily large, it's not any more of a good dog than the two original dogs.
}}

==Explanation==
{{incomplete|Do NOT delete this tag too soon.}}
Beret Guy and Cueball are walking Beret Guy's dogs when BG makes a comment on how interferometry is really cool. Interferometry is the practice of overlapping two different waves to get a different signal, which can be used to determine the distance between two reflecting surfaces. Beret Guy states that two dogs placed at a consistent interval will function as a larger dog. While this idea works on waves, it probably won't work on dogs, which is why Cueball is confused and starts to correct him. Before he can respond, however, Beret Guy jumps on this "large" dog and appears to be floating in midair. The large dog is further proved when it gives out a large bark. Cueball looks on confused while Beret Guy appears to break more laws of physics, again.

This comic is a reference to {{w|Astronomical interferometer|Astronomical Interferometers}}, arrays of separate telescopes that work together as a single telescope to provide the higher angular resolution of a single larger telescope, using a process known as {{w|Aperture Synthesis}}.

The title text states that the effective giant dog is not any more 'good' than the two original dogs. This is analagous to sensitivity for astronomical interferometers. Interferometery does not increase the light-gathering area, so it cannot view dim objects as well as a single large telescope could.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
[Beret Guy and Cueball are walking with their dogs.]
Beret Guy: Interferometry. Is so cool!

[The two dogs are placed a small distance apart.}
Beret Guy: If you put two small dogs a large distance apart, they can function as a larger dog.

Cueball: I'm not sure that's-
[He is cut off by Beret Guy jumping onto an invisible steed, most likely the "bigger dog".]
Beret Guy: HYAH!

Beret Guy: Away!
[He rides away on the invisible dog with the two smaller dogs under him, while the invisible dog gives out a large bark.]

{{comic discussion}}

Talk:1208: Footnote Labyrinths

2017-03-17T14:58:46Z

162.158.34.4:

Way to nerd-snipe me, Randall. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 04:52, 6 May 2013 (UTC)

In the nested-footnotes interpretation, 5 has to be ignored: The 6 must be true, and the 6 says that it’s “actually a 1”, but with footnote 2+2 which says “ibid.” and thus equals footnote 3, which is true. So 6 really ''does mean'' actually a 1, which leaves 5 to be ignored. --[[Special:Contributions/77.186.8.191|77.186.8.191]] 10:47, 6 May 2013 (UTC)

The footnote for 6 is actually 1 to the 2 to the 2 [[User:Schmammel|Schmammel]] ([[User talk:Schmammel|talk]]) 12:36, 6 May 2013 (UTC)

Explaination is wrong : abc = a(bc) = ab^c (confer the definition of a gogol = 10^100 = 10102, and a gogolplex = 10^gogol = 10(10100), not 10^110. So since 1^2= 1, No12 really means No1. {{unsigned ip|192.54.145.66}}
:Yes, so "no1" means to ignore the "no" and the answer for the second explanation is "we found evidence for the data." By the way, it's spelled "googol." [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 17:51, 6 May 2013 (UTC)

;Question, alternative explination

I wasn't really satisfied with the whole discarding of the infinite loop, so I worked through the problem seperately using the nested footnotes. Then, when we hit the infinite loop I split between the two possible answers (either the infinite loop ends on true or false). As I read it, they both get the same answer:

no (3)

no (not true (5))

no (not true (true (2 < 6 < 3))

no (not true (true (2 < 6 < (not true))))

no (not true (true (2 < (actually 1 < 2 < 2 (not true 3 < 2)))))

no (not true (true (2 < (actually 1 < 2 < 2 (not true (5)))))

Split!

If 6 is false (infinite loop possibility)

no (3 < 5 < 2)

no (not true (7)) - meaningless, so discard

no (not true)

If 6 is true (infinite loop possibility)

no (3 < 5 < 1 < 2 < 2)

no (3 < 5 < 1 < 4)

no (3 < 5 < 1)

no (3)

no (not true)

Both lead to the answer "... experiments to observe this and we found evidence for it in our data". {{unsigned|‎Urah}}

:Yes, but at each stage you may "''toggle between interpreting nested footnotes as footnotes on footnotes and interpreting them as exponents (minus one, modulo 6, plus 1).''" That is, a23 may ''either'' be read as "apply note 8 (=2mod6) to text ''a''", or as "apply note 3 to text "2", then the result to text ''a''". {{unsigned ip|192.54.145.66}}
:There are differences in interpretation here. If we write "foo36", is it equal to "foo112" or "foo3112"? I assumed the former and you assumed the latter. My reasoning is that footnotes modify their arguments and not themselves. [[User:Alpha|Alpha]] ([[User talk:Alpha|talk]]) 17:44, 6 May 2013 (UTC)

Shouldn't 5 be true (because 6 is actually 13; therefore 5 is true2133; so the 2 is ignored regardless the truth of 3) and 3 is not true? Sebastian --[[Special:Contributions/178.26.118.249|178.26.118.249]] 18:35, 6 May 2013 (UTC)

'''Yet another alternative solution:''' Footnotes should be evaluated from top to bottom, so "no12" = "no1 + 2" = "no3". We turn to the definition of 3, which is "not true32" = "not true3 + 2" = "not true5".

Now 5 is "true263". The 6 says that the 2 footnote is really 122 = 1(4. ibid.) = 13, but the 3 tells us that the 6 is "not true5", getting us into an infinite loop. However, 263 must evaluate to 1, because otherwise we're incrementing "true" by 2, which is meaningless. This means that 3 must be equal "not true". 63 = "actually a 1"33 = "actually a 1". 5 becomes true1 which just says to ignore this footnote altogether and we can confirm that 3 is indeed not true (not true5 = not true). So the answer is that the "no" is not true, and the correct statement is "we found ''some'' evidence for it in our data." Phew. [[User:Ciamej|Ciamej]] ([[User talk:Ciamej|talk]]) 22:40, 6 May 2013 (UTC)

I'm not discouraging anyone from coming up with more alternate solutions, but would it be fair to say that part of the point is that there are multiple equally legit ways to run this labyrinth, and that some exit where you ignore the 'no', others exit on the other side where you don't ignore it. and then there's those who won't exit because they're busy making a map. - [[Special:Contributions/70.72.16.171|70.72.16.171]] 23:18, 6 May 2013 (UTC)

I don't understand the proof from ''This means that 3 = "true"''. Why do you assume that footnote has to be either "true" or "false? I think it could be "ignore this", "increment by three before following", "leave the whole calculation and assume we have two pieces of evidence" etc. as well. [[Special:Contributions/178.56.1.144|178.56.1.144]] 23:37, 6 May 2013 (UTC)
:Given the footnotes' definitions I don't think it's possible to ever come up with "increment by three before following" ;)
:Actually the solution I gave may be not strictly formal, but it gives some intuition why it seems to be the only valid one.
:The fact that the definitions are recursive doesn't imply that the ultimate answer cannot be resolved. [[User:Ciamej|Ciamej]] ([[User talk:Ciamej|talk]]) 02:18, 7 May 2013 (UTC)

So what I'm hearing is this, "No means No.", yes?[[Special:Contributions/66.88.136.254|66.88.136.254]] 19:37, 8 May 2013 (UTC)

It's a real strange logic, but "No = No" means "Yes" --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:44, 8 May 2013 (UTC)

;Footnote logic:

So... I did some footnote logic, and came up with this:

This explanation will treat footnotes as footnotes, with the order of operations from top-down, with footnotes acting on only the object they are attached to, including other footnotes.

1. no^1^2

2. no^3

3. no(not true^3^2)

4. no(not (true^5))

5. no(not (true^2^6^3))

The ^6 says the ^2 is actually a 1^2^2, but the ^3 says that the ^6 is "not true^3^2". This leads us to an infinite loop, as the "not true^3^2" in step 3 led to the addition of the additional "not true^3^2".

I assume that the loop can be reduced down to either "true" or "not true", for the purposes of following this path. I will explore both options.

if infinite loop is true:

6a. no(not true^1^2^2) (replacing 2 with 1^2^2 as per 6)

7a. no(not true^1^4)

8a. no(not true(ignore(not true^3^2))) (infinite loop again)

I guess we'll split once more.

if second loop is true:

9aa. no(not (true(ignore(not true)))) (as the second loop reduced to true, we have no more footnotes)

10aa. no(not true) (since the "ignore" this exponent was not true, we can remove it)

And we finally have something simple. No is not true, so evidence was actually found.

if second loop is false:

9ab. no(not (true(ignore(not (not true))))) (again, with the second loop reduced to "not true", we have no more footnotes)

10ab. no(not (true(ignore)))

11ab. no(not)

This is a bit more confusing, as we're ignoring the true as per step 10ab, and are just left with no^not. I'm going to take this to mean true, as in, again, evidence was found.

if first loop is false:

6b. no(not (true^2)) (the ^6 which said that the ^2 was actually a 1^2^2 was negated by the ^3 (which we declared as false for this leg), therefore both the ^3 and the ^6 can be reduced to nothing.)

No idea how to proceed here, as true is not a footnote, and can't be followed or incremented.

If we just ignore the ^2, we're left with the same as 10aa. That is, evidence was again found.

Alternatively, we can say that because ^5==false led us to a nonsensical result, then ^5 must always reduce to true, meaning that the only acceptable answer is to follow the path to 10aa.

Any way you slice it, evidence was certainly found.

[[User:Kalzekdor|Kalzekdor]] ([[User talk:Kalzekdor|talk]]) 22:29, 25 May 2013 (UTC)

;Read the title text
The title text says that you have to toggle between interpreting footnotes and calculating them (minus one, modulo 6, plus 1). And all calculations using the plus sign for exponents are wrong. 32 is 3*3 and not 3+2.

:Interpreting footnotes:
:no12 - 1ignore this
:no2 - 2increment by 2
:no4 - 4IBID -> footnote before
:no3 - 3not true32
:yes32

:Calculation:
:32 = 9 -> 9-1 = 8 -> 8 modulo 6 = 2 -> 2 plus 1 = 3
:yes3

:Interpreting footnotes is again the same as before:
:yes3
:no32

So I am also on an infinite loop and footnotes 5 and 6 are never used.
--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 11:29, 26 May 2013 (UTC)

you are all wrong and I would presume there is no solution as title popup says '''every time''' you read it you should toggle... so I'm afraid everyone could arrive to different solution.
[[Special:Contributions/87.239.45.58|87.239.45.58]] 12:55, 26 June 2013 (UTC) Cyp

(A) I don't follow the last comment. You toggle only when you read the mouseover. For most people, only once: i.e., try it the other way.
(B) Should 1 be interpreted as a message to the reader or a comment on the footnoted phrase? If the latter, then as exponents, it is 1x1=1, or ignore the "no". If the former, then as exponents, move on to footnote 2, then 4, then 3 and stop there--"not true 3x3" cannot be evaluated. When interpreting as footnotes, then the footnote on No1 also cannot be evaluated as footnote 3 is an endless loop of 3-2-4-3-2-4... There is no opportunity to arbitrarily stop at "true" or "not true" as one commenter suggests because one never reaches the point of evaluating the self-referential 3 on the third footnote. Or it so it seems to me. [[Special:Contributions/114.171.110.105|114.171.110.105]] 14:03, 11 July 2013 (UTC)

;Where is the EDIT WAR here???
There is an update here today to the latest update on November 17. 2013; where is the actual WAR??? --[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 01:35, 8 January 2014 (UTC)
:I am the anonymous editor who made the last edit before the page was protected. I suspect my frustrated summaries made the administrators believe there was a war. [[Special:Contributions/199.27.128.146|199.27.128.146]] 17:53, 13 January 2014 (UTC)

I see it in a a different way.
no ^ 1 ^ 2 means footnote 1) to the word "no" and footnote 2) to footnote 1. Thus we got:
No (ignore this) (2)
no (ignore this) (increment by 2 before following) - so use 4) instead of 2)
no (ignore this) (4)
no (ignore this (ibid) - so use 3) instead of 3)
no (ignore this) (3)
no (ignore this) (not true) (3)(2)
As 2) take us to 3) via 4) we got
no (ignore this) (not true) (3)(3)
Now we can replace both (3)'s with '(not true) (3)(2)', but... they are the same. It does not matter if they are true or not, because we can A) apply 'not true' to the phrase 'not true', which results in 'true', or B) apply 'true' to the 'true' phrase, which results in the same answer, so:
no (ignore this) (not true)
Not true makes us ignoring footnote 1, and in consequence, footnoted 'no' from the very beginning stays the same.
I could alt, but It's 4p.m. and I'm heading home from office. 8-)
[[Special:Contributions/141.101.88.219|141.101.88.219]] 13:58, 26 September 2014 (UTC)Koovert

testing a thing here
jc