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Feb
19
comment Why does the Sun turn red near sunset?
yes, redshift from Doppler effects are negligible (40'000 km / day is about $1.5 \cdot 10^{-6}$ of the speed of light). If the redshift were responsible for the sunlight turning red in the evening one would expect it to be affected equally by blue shift in the morning...
Feb
19
comment Why does the Sun turn red near sunset?
I've seen many red sunrises. Are you sure you start watching the sun in the morning at the same altitude (height above the horizon) as you experience it red in the evening ? Is the region west of you more dusty than the area east of you (e.g. land on the west, sea on the east) ? Is air pollution in your area stronger in the evening than in the morning ?
Feb
18
revised Why does the Sun turn red near sunset?
edited body
Feb
18
answered Why does the Sun turn red near sunset?
Dec
23
comment Possible values of energies and impulses of virtual photon emitted by real electron
if you mean the photon and electron at the time corresponding to the the middle of this graph, there is not a single possible energy for them but there is a range of energies (following a probability distribution).
Nov
20
comment Using gravity to send messages (at the speed of light)
why not using light (or electromagnetic waves in general) to send messages at the speed of light ?! Gravitational wave detectors such as LIGO, LISA and VIRGO are quite large and complicated...
Oct
9
comment What are the strongest sources of collimated neutrons and protons?
interesting project ! But the current seems to be 0.019 mA (so in the lower region of the above diagram) and probably up to 106 keV (i.e. 0.000106 GeV)
Oct
9
comment Spin of a decay product
It's not clear in which case 'spin' means 'spin state' (current angular momentum projection) and which case 'spin' means 'property of a particle' (maximum possible angular momentum projection). Also, consider taking into account the orbit spin of the A,B,C system.
Oct
8
comment What are the strongest sources of collimated neutrons and protons?
A note on the 500mA of beam current of the LHC: these protons make 11'000 revolutions per second. If your experiment would absorb or otherwise destroy the beam, you could only use 1/11'000 of the 500 mA (I found that the highest beam intensities in 2012 were about $229\cdot10^{12}$ protons per beam). On the other hand, whether the beam is bunched or continuous does not affect the (time averaged) current.
Oct
6
comment Chance of objects going against greater entropy?
compare (the inverse of) $10^{-10^{23}}$ or $10^{-10^{19}}$ to the estimated number of atoms in the observable universe (estimated to be $10^{80}$) and you'll realize it is really small...
Oct
6
comment Is it possible for the entropy in an isolated system to decrease?
see e.g. physics.stackexchange.com/a/547/671 for a discussion of how small this 'pure chance' typically is for macroscopic systems... (and compare this to the number of atoms in the observable universe which is estimated to be $10^{80}$)
Sep
25
comment Sharp cut-off, quadratic corrections and naturalness
a theory should be considered valid as long as it does not contradict experimental observations. And in principle, no new physics phenomena beyond the Standard Model may turn up which means we would have to set the cutoff parameter to a value comparable to the Planck scale (which is a 'fine tuning problem'). One way of interpreting the cutoff scale is the scale up to which the Standard Model is valid and at which a new physics phenomena appear (which then can e.g. cancel these divergencies).
Sep
24
answered Translation operator to higher order
Sep
20
awarded  Yearling
Sep
20
comment What are the strongest sources of collimated neutrons and protons?
The sun for example must emit a very high number of protons per second (and I bet there are other sources in the universe), but admittedly these are not very focused...
Sep
20
answered What are the strongest sources of collimated neutrons and protons?
Jul
16
comment Is Electromagnetic Mass Possible?
The Meissner effect comes to my mind when I read 'electromagnetism' and 'mass'...
Jul
10
comment Maximum theoretical bandwidth of fibre-optics
I would imagine that some dark fibres (fibres to be used in the future) are installed at the same time
Jul
10
comment Maximum theoretical bandwidth of fibre-optics
also, FTTH is often implemented as a passive optical network (using time multiplexing) meaning that each end user will share the bandwidth of the fibre with other users.
Jul
10
comment Canonical everyday-life example of a technology that could not work without humans mastering QM in analogy to the application of GR in GPS?
this is a quite delicate question: looking at the timeline of the solar cell it looks like the first solar cell was built in 1883 while Einstein postulated the quantum nature of the photoelectric effect only later in 1905. So it could be that without quantum mechanics, we would be able to build certain devices without understanding why they work.