UNIVERSE IS FINITE OR INFINITE?

Art by Moonrunner Design

At present there is no answer to this question. However I will try to list the hypothesys currently on the table with related issues.

Probably the first question to ask in order to address the problem is: space and time start with the Big Bang or they existed even before? (for this question actually there is no answer...)

• If space and time begin with the Big Bang then the next step is to consider that the distances are measured not only in space but also in time.
The universe has been expanding since its birth (which occurred - if the Big Bang theory is correct - about 13 billion years ago) following the Hubble's law: each point is moving away more quickly from one another as much as they are distant. Since, however, the birth of the universe is fixed in time, and being the expansion rate not infinite, logic suggests that "actually" the size of the universe is finite.
When we ask: what is the size of the universe? ... therefore we should also ask: at what time?
In this scenario an answer on the size of the universe is closely linked to time. If the expansion continues for an infinite time, the universe would have an infinite dimension to infinite time.
The real question then becomes: what is the fate of the universe? The universe will expand forever or at some point the expansion will end and the universe will collapse on itself?
We still have no definitive answer to this question.

• If space and time existed before the Big Bang, our universe was born in a particular area of an existing space-time.
In this scenario it is not clear if we can find answer to this question.

► Additional resources>>

http://blogs.scientificamerican.com/degrees-of-freedom/httpblogsscientificamericancomdegrees-of-freedom20110725what-do-you-mean-the-universe-is-flat-part-i/

http://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html

► Image Credit:
Art by Moonrunner Design

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Astrophysics collection (March 11, 2016)

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ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

A BINARY ORIGIN FOR A CENTRAL COMPACT OBJECT (CCO)?

Figure: False-Colour X-ray and infrared emission image from the core of the infrared shell. The RGB colours correspond to Chandra X-ray 0.2-10 keV (blue), IRAC infrared 8 μm (green), and HPACS 70 μm (red) data. The intensity scale is logarithmic for all channels. Overlaid are equal brightness levels from the MIPS 24 μm band. Note that around the CCO the infrared emission is suppressed in the 70 μm band and enhanced in the 24 μm band suggesting higher dust temperature. Credit: Doroshenko et al 2016 Central compact objects (CCOs) are thought to be young isolated neutron stars that were born during the preceding core-collapse supernova explosion.

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