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  • 23 votes cast
Jan
31
comment Can the Earth leave orbit if the population of humans and other live forms increases?
Since trees and angular momentum have been mentioned in the comments, another slightly related fun fact: When trees collectively lose their leaves in autumn (and most of affected trees are on the northern hemisphere, so we talk about northern autumn here), there is a measureable (not with your writs-watch, though) speed-up of the Earth spinning.
Jan
15
comment Why is 7 TeV considered as a big amount of energy?
I assume $1.15\times 10^{11}$ is an approximate number related to the machine picking up "a handful" of protons. But what is the significance of the precise number 2808? (E.g., why is that not just "about 3000"?)
Jan
12
comment 3D glasses giving the opposite effect to that expected
Some followup: As seen from the sketch, the green dots should never be further apart than the viewer's eys (6.6 cm for me, possibly less for kids). But what if a movie with (nearly) infinitely far objects is shown in different cinemas with different screen sizes? Wouldn't either small screen cinemas bring those objects into finite distance, or super-large screen cinemas produce "impossible" images (the two copies more than 6.6cm apart)?
Nov
28
comment How to keep a helium balloon between 1 to 5 meters above ground? (without it being tied)
Doesn't the cargo pulling on the balloon hull tangentially introduce an inward force, i.e., increased pressure?
Oct
29
comment What does an undefined formula in physics mean?
More to the point, there are hardly any cases of an actual $0$ in physics (i.e., the vacuum is not so vacuous at all, etc.)
Sep
9
comment Why are there no stars visible in this photograph?
This question reminds of the argument of some hollywood-moon-landing-conspiracy theorists that NASA "forgot" to add stars to their "fake" photos, whereas the lack of stars is easily explained by exposition considerations
Sep
5
comment Twins Paradox - Does ageing depend on motion?
Krebs cycle or not, all clocks onboard that ship differ by the same factor (except that some are more precise than others), be it radioactive decay, the turntable of an old-fashioned record player, a tuning-fork, the number of times you take a breath, your heartbeat, the number of times you sleep naturally, the "number of thoughts" you have, the number of rounds of Super Mario you play. For all it takes, the travelling brother cannot infer from any of these (also travelling) "clocks", including his psychological perception of time passed, whether his ship is at rest or moving fast.
Aug
18
comment Impossibility of time travel due to energy conservation?
@JohnRennie Yeah, on the other hand it seems that the Terminator movies use time travel mechanisms that we don't know of :)
Aug
14
comment Is there experimental verification of the s, p, d, f orbital shapes?
See, I always knew that elecron clouds are light blue :)
Jul
25
comment Can a building get taller at night?
This suggests the followup question: How does the height difference caused by different weight loads compare to height differences by different (outside) temperatures?
Apr
27
comment Why do electrons, according to my textbook, exist forever?
Also, there is perhaps only one single electron that keeps travelling back (as positron) and forth trough time ;)
Apr
4
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Apr
4
answered Does a capacitor ever get fully charged?
Mar
29
comment If the Earth is a good conductor of electricity, why don't people get electrocuted every time they touch the Earth?
Walking barefoot on a heavily charged planet would rather cause you to take up some of the charge and float away
Mar
23
comment What if you opened a door in a spaceship without a spacesuit?
Space is so big indeed, that the simple Avogadro explanation about air filling the void is no longer fully accurate - in fact once outside the airlock, your air molecules won't ever meet again so that usual laws of gases don't apply. The molecules just start (and keep) moving straight away at their thermal velocity of some hundred meters per second.
Mar
19
comment Could we send a man safely to the Moon in a rocket without knowledge of general relativity?
But if we hadn't gotten a man to the Moon (without accounting for GR), the good measurements of the position would not be possible at all (you do use the retroreflector, don't you?)
Mar
15
comment Is it possible to watch the same distant star's supernova event twice?
@HenningMakholm Well, if there are two (or more) geodesics from the nova event to us, why should they be of equal length in the first place? Also, even if I observe from two angles simultanuously, the notion of simultanity is relativistically meaningless away from my personal position where both rays go through different points in space ...
Feb
4
comment Is there a limitation on Gauss' law?
@levitopher The misconception that "infinite sums" are sums is also what makes people think that $1+2+3+4+\ldots$ should mean $\infty$ (or possibly be undefined if one abhorrs infinity), but certainly not $-\frac1{12}$. Fact is that all three of these interpretaions make sense depending on context. If those beast were sums there'd be no ambiguity
Jan
15
comment Heat Transfer From a Spaceship in Deep Space
@pentane The 880 K difference mean that your 290 K environment radiates back 880 W at you. - The equilibrum temperature of 180 K is based on the assumption that the bodily exothermal processes are still active and emitting 120 W. Of course, the fatality of cooling down even to 180 K will make these processes stop and then pave your way to 3 K.
Oct
15
comment Which dissipates more power, a small or big resistor?
(Yeah, try this experiment with constant curretn - but don't try it at home)