141 reputation
5
bio website von-eitzen.de/math/tntrep.xml
location Bonn, Germany
age 49
visits member for 2 years, 11 months
seen 19 hours ago

I did study math and had a knack for it, but I am sooo out of that business now ...


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
awarded  Teacher
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)
Oct
15
comment Which dissipates more power, a small or big resistor?
As a consequence, the voltage source gets undesirably hot as well (it dissipates the same power at the optimum).
Sep
25
awarded  Commentator
Sep
25
comment Did the Big Bang happen at a point?
ONe might say: Yes, it happened at a single point, namely everywhere (which made no difference "then")
Aug
10
comment Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?
In a way, the Sun is faster than a nuclear bomb. It emits the $E=mc^2$ equivalent of four million tons of matter per second, whereas a nuclear bomb converts only a tiny fraction of its mass (when we talk about a four megaton bomb, this refers to the chemical energy contained in 4 million tons of TNT).
Jul
10
comment Special relativity and electromagnets
The moving electrinns are cordially invited to be denser in the lab frame, but that would create forces driving them apart, thus "fleeing" from the wire along the current until neutrality is attained. Of course, with an infinite wire we may run into different theoretical trouble (we couldn't get the current running at the full length at once, we would have waves propagating, ...)
Apr
5
comment Why is jumping into water from high altitude fatal?
Even a "graceful diuver" entering vertically, toes ahead, will suffer from the following: The toes start accelerating with $770g$ about $0.01s$ before the head enters; per $\frac12at^2$ they have moved up (relatively) by $\approx 37cm$ then and move with $\approx 75m/s$ towards the head. That doesn't sound healthy.
Feb
16
comment Is it fair to judge this speedskating race by only 3 thousands of a second?
Don't forget the position of the sun which by its gravity influences time ...