On Randomness in Quantum Mechanics

The quantum mechanical probability densities are compared with the probability densities treated by the theory of random variables. The relevance of their difference for the interpretation of quantum mechanics is commented

Observables have no value: a no-go theorem for position and momentum observables

A very simple illustration of the Bell-Kochen-Specker contradiction is presented using continuous observables in infinite dimensional Hilbert space. It is shown that the assumption of the \emph{existence} of putative values for position and momentum observables for one single particle is incompatible with quantum mechanics.Comment: 6 pages, 1 Latex figure small corrections, refference and comments adde

"Hair for freedom" movement in Iran : interreligious dialogue in social media activism?

After the death of Masha Amini at the hands of the Iranian Morality Police for not wearing the hijab, in accordance with what they considered appropriate in September 2022, a social media campaign called "Hair for Freedom" was sparked on different platforms, with videos of women cutting their hair in protest over Iranian women's rights and Amini's death. This paper analyzes whether this digital feminist movement enacted an interreligious dialogue (IRD). Based on content analysis and topic modeling of the publications retrieved from three major platforms, Twitter, Instagram, and TikTok, the results indicate that this was mainly a Western movement focused on women's bodies as a political symbol in authoritarian Islamic regimes and has not achieved an IRD since most social media posts reproduced the hashtag #HairForFredom without opening a religious discussion. As observed in other digital movements, conclusions indicate that social media activism does not offer an opportunity to engage in dialogues to enlightenthe public sphere. On the contrary, the focus appears to provide users with the opportunity to enhance their reputation by engaging in popular social media campaigns that promote social change

Long term X-ray spectral variability of the nucleus of M81

We have analysed the soft X-ray emission from the nuclear source of the nearby spiral galaxy M81, using the available data collected with ROSAT, ASCA, BeppoSAX and Chandra. The source flux is highly variable, showing (sometimes dramatic: a factor of 4 in 20 days) variability at different timescales, from 2 days to 4 years, and in particular a steady increase of the flux by a factor of >~ 2 over 4 years, broken by rapid flares. After accounting for the extended component resolved by Chandra, the nuclear soft X-ray spectrum (from ROSAT/PSPC, BeppoSAX/LECS and Chandra data) cannot be fitted well with a single absorbed power-law model. Acceptable fits are obtained adding an extra component, either a multi-color black body (MCBB) or an absorption feature. In the MCBB case the inner accretion disk would be far smaller than the Schwartzchild radius for the 3-60X 10^6 solar masses nucleus requiring a strictly edge-on inclination of the disk, even if the nucleus is a rotating Kerr black hole. The temperature is 0.27 keV, larger than expected from the accretion disk of a Schwartzchild black hole, but consistent with that expected from a Kerr black hole. In the power-law + absorption feature model we have either high velocity (0.3 c) infalling C_v clouds or neutral C_i absorption at rest. In both cases the C:O overabundance is a factor of 10.Comment: 30 pages with 15 figures. Accepted for publication in the Astrophysical Journa

Brownian Entanglement

We show that for two classical brownian particles there exists an analog of continuous-variable quantum entanglement: The common probability distribution of the two coordinates and the corresponding coarse-grained velocities cannot be prepared via mixing of any factorized distributions referring to the two particles in separate. This is possible for particles which interacted in the past, but do not interact in the present. Three factors are crucial for the effect: 1) separation of time-scales of coordinate and momentum which motivates the definition of coarse-grained velocities; 2) the resulting uncertainty relations between the coordinate of the brownian particle and the change of its coarse-grained velocity; 3) the fact that the coarse-grained velocity, though pertaining to a single brownian particle, is defined on a common context of two particles. The brownian entanglement is a consequence of a coarse-grained description and disappears for a finer resolution of the brownian motion. We discuss possibilities of its experimental realizations in examples of macroscopic brownian motion.Comment: 18 pages, no figure

An alternative approach to the construction of Schur-Weyl transform

We propose an alternative approach for the construction of the unitary matrix which performs generalized unitary rotations of the system consisting of independent identical subsystems (for example spin system). This matrix, when applied to the system, results in a change of degrees of freedom, uncovering the information hidden in non-local degrees of freedom. This information can be used, inter alia, to study the structure of entangled states, their classification and may be useful for construction of quantum algorithms.Comment: 6 page

XMM-Newton survey of the Local Group galaxy M 33

In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. We correlate these newly detected sources with earlier M 33 X-ray catalogues and information from optical, infra-red and radio wavelengths. As M 33 sources we detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources, and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations we would expect 175 to 210 background sources in this field. This indicates that about half of the sources detected are sources within M 33.Comment: 14 pages, 6 figures, accepted for publication in A&A, the images of Figs. 1,2,3,4,6 are available in jpg format, a full version of the paper is available at ftp://ftp.xray.mpe.mpg.de/people/fwh/docs/M33_AA0068.p