• Alexander Chepick added an answer:
    Are the small anisotropies found in the cosmic microwave backgroung also evidence for the accelerated universe?

    I am an observational astrophysicist. From my perspective, the type Ia supernovae are the most important and clear evidence for the present accelerated phase of the universe. However I read a theoretical paper arguing that the very small anisotropies found in the CMB are also evidence for the accelerated expansion. How come? What is the realation?

    Alexander Chepick

    Dear João,

    If we assume that GR applies to the whole Universe, that there was a Big Bang, then you can do some of the conclusions, and if we assume that the universe is static and GR are not applicable to the entire Universe, then the conclusions will be quite different.

     You does not must write in answer to your question, "there was the beginning of times, there was recombination," as about established facts. You need to answer:
    "If we assume that the Einstein equations are applicable to the entire Universe that the universe is expanding, starting from the moment when nothing was, then ... .

    But if we assume that the universe is eternal, infinite and static, then ..."

    Уважаемый João,
     Если предположить, что GR применима ко всей Вселенной, и если предположить, что существовал Большой Взрыв,  то тогда можно делать одни заключения, а если предположить, что Вселенная статическая и GR неприменима ко всей Вселенной, то тогда выводы будут совсем другие.

    Нельзя в ответе на ваш вопрос написать, «было начало времен, была рекомбинация», как будто это установленные факты. Нужно отвечать:
    «Если предположить, что уравнения Эйнштейна применимы ко всей Вселенной, что Вселенная расширяется, начиная с момента, когда вообще ничего не было, то ….
    А если предположить, что Вселенная является вечной, бесконечной и статической, то …» 

  • Ksh. Newton Singh added an answer:
    Does a free fall collapsing dust radiate gravitational waves?

    A collapsing star when explode (supernova), due to the sudden ejection of massive mass around the central core, there is a disturbance in space-time leading to emission of gravitational waves. But what will happen if a collapsing goes on till black hole is formed, without any explosion? Will there be an emission of gravitational waves due to the continuous grow in curvature because of the growing mass?

    Ksh. Newton Singh

    Thank You Dr. Yang

  • Daniel Pfenniger added an answer:
    Can anyone help me with a question about neutrinos?

    I recently read a paper saying that, apart from those coming from stars, supenovae, cosmic rays and nuclear power plants, the majority of all the neutrinos in our universe were created at the big bang. But, considering that neutrinos are very elusive particles, that they travel almost at the speed of light and in straight lines, I think they all should be now near the boundary of the universe.

    How come that we can observe them? Is my reasoning above not right?

    Daniel Pfenniger

    Cosmologists keep saying the neutrino background has temperature T=1.9K while actually they want to say that their energy corresponds to kT, with k Boltzmann's constant.  This habit comes from the time neutrinos were commonly assumed to be massless.  In that case, like for photons, energy can be assimilated to a temperature because if they would thermalize with a thermometer a temperature T would be measured.

    But since neutrinos are massive, nowadays a substantial part of their energy is in their rest mass c^2.  A thermometer only measures the random kinetic energy part.  The  temperature that would be measured  if a huge thermometer would be brought to thermal equilibrium with the the neutrino background would be rather in the 0.001K range (depending on their still uncertain actual mass).

  • John Wyndham added an answer:
    Has the important astronomical event, supernova 1054 in constellation Taurus, played any role in the discovery of pulsars?
    I know that the development of radio astronomy was the most crucial step in the discovery, but still I am convinced that the supernova 1054 may have had some inspiring role in the discovery of pulsars.
    John Wyndham

    About myself:

    I have not worked in the field of Radio Astronomy since leaving Caltech in 1967.

    My purpose in joining ResearchGate was to feature my recent researches into the Science of 9/11.  A paper presented at the 2014 IEEE International Conference on Ethics in Science, Engineering etc (May 23-26, 2014, Chicago) is awaiting publication in the IEEE proceedings for this conference. The title of the paper is "Ethics and the Official Reports about the Destruction of the World Trade Center Twin Towers (WTC1 and WTC2) on 9/11: A Case Study" by John D. Wyndham, Wayne H. Coste, and Michael R. Smith.

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