Wyniki wyszukiwania - BazTech

Ograniczanie wyników

3 Acta Astronomica

Znaleziono wyników: 3

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: Cosmology: theory

Sortuj według:

Ogranicz wyniki do:

A Short Answer to Critics of Our Article "Eppur si Espande"

Abramowicz M. A., Bajtlik S., Lasota J.-P., Moudens A.

Acta Astronomica

2009

Vol. 59, No. 1

131--135

Recently we presented a formal mathematical proof that, contrary to a widespread misconception, cosmological expansion cannot be understood as the motion of galaxies in non-expanding space. We showed that the cosmological redshift must be physically interpreted as the expansion of space. Although our proof was generally accepted, a few authors disagreed. We rebut their criticism in this Note.

Are Gamma-Ray Bursts a Standard Energy Reservoir?

Li L.- X.

Acta Astronomica

2008

Vol. 58, No. 2

103--112

One of the most important discoveries in the observation of gamma-ray bursts (GRBs) is that the total energy emitted by a GRB in γ-rays has a very narrow distribution around 1051 erg, which led people to claim that GRBs are standard energy explosions. As people made the claim they have ignored the selection biases which must be important since GRB observations are strongly fluence or flux-limited. In this paper we show that, when the selection effects are considered, the intrinsic distribution of the GRB energy can be very broad. The number of faint GRBs has been significantly underestimated because of the fluence or flux limit. The bright part of the distribution has been affected by another important selection effect arising from the beaming of GRB jets, which is instrument-independent and caused by the fact that brighter GRBs tend to have smaller jet angles and hence smaller probabilities to be detected. Our finding indicates that GRBs are not a standard energy reservoir, and challenges the proposal that GRBs can be used as standard candles to probe cosmology.

Eppur si Espande

Abramowicz M. A., Bajtlik S., Lasota J.-P., Moudens A.

Acta Astronomica

2007

Vol. 57, No. 2

139--148

The rather wide-spread belief that cosmological expansion of a flat 3D-space (with spatial curvature k=0) cannot be observationally distinguished from a kinematics of galaxies moving in a flat and non-expanding space is erroneous. We suggest that the error may have its source in a non relativistic intuition that imagines the Universe not as a space-time but separates space from time and pictures the cosmological expansion as space evolving in time. The physical reality, however, is fundamentally different - the expanding Universe is necessarily a curved space-time. We show here that the fact that the space-time is curved implies that the interpretation of the observed cosmological redshift as being due to the expansion of the cosmological 3D-space is observationally verifiable. Thus it is impossible to mimic the true cosmological redshift by a Doppler effect caused by motion of galaxies in a non-expanding 3D-space, flat or curved. We summarize our points in simple space-time diagrams that illustrate a gedanken experiment distinguishing between expansion of space and pure kinematics. We also provide all relevant mathematics. None of the previously published discussions of the issue, including a recent popular Scientific American article by Lineveaver and Davis, offered a similarly clear way out of the confusion.