Today’s Shared Post_Link: 14 March 2017

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Today’s Shared Post-Link…
Published Date: 03.14.2017 

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“The Universe itself may be finite or may be infinite; the jury is still out. But one thing is certain: the part that’s accessible to us is finite. Even with the expanding Universe, even with all the galaxies and stars and planet and molecules and atoms and subatomic particles in it, there’s only so much we can access. And those limitations — the total numbers of particles and the total amount of energy available in the Universe — means there’s only a finite amount of information we can determine about our cosmos. For the first time, we can quantify that, and begin to infer which things we might never understand.” …

The Hubble eXtreme Deep Field, our deepest view of the Universe to date.
Image credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch,
University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team.

“When we found that the more distant a galaxy was from us, on average, the faster it appeared to be receding from our perspective, an intriguing possibility opened up, consistent with Einstein’s General Relativity: perhaps the galaxies were not all speeding away from our location, but the fabric of space itself was expanding. If this were the case, then the Universe should not only be expanding but cooling, as the wavelength of light would be stretched to lower and lower energies as time went on. Moreover, we didn’t just have to extrapolate forwards, but we could go backwards, too: to a time where the Universe was smaller in the past.” …

“And yet, when we viewed our Universe, it did have stars and galaxies; it was the same temperature in all directions, and it didn’t have these high-energy relics.” …

The history of the Universe, as far back as we can see using
a variety of tools and telescopes.
Image credit: Sloan Digital Sky Survey (SDSS), including the current depth of the survey.

“The solution to these problems was the theory of cosmic inflation, which replaced the idea of a singularity with a period of exponentially expanding space, and which predicted those initial conditions that the Big Bang on its own could not. In addition, inflation made six other predictions for what we would see in our Universe:

  1. A Perfectly Flat Universe.
  2. A Universe with fluctuations on scales larger than light could’ve traveled across.
  3. A Universe with a maximum temperature that’s not arbitrarily high.
  4. A Universe whose fluctuations were adiabatic, or of equal entropy everywhere.
  5. A Universe where the spectrum of fluctuations was just slightly less than having a scale invariant (ns < 1) nature.
  6. And finally, a Universe with a particular spectrum of gravitational wave fluctuations.” …

How cosmic inflation gave rise to our observable Universe,
which has evolved into stars and galaxies and other complex structure by the present.
Image credit: E. Siegel, with images derived from ESA/Planck and the DoE/NASA/ NSF
interagency task force on CMB research. From his book, Beyond The Galaxy.

“The next logical question about our origins, of course, then becomes that of where did inflation come from? Was it a state that was eternal to the past, meaning that it had no origin and always existed, right up until the moment it ended and created the Big Bang? Was it a state that had a beginning, where it emerged from a non-inflationary state in spacetime some finite time in the past? Or was it a cyclical state, where time looped back on itself from some far future state?” …

“The difficult thing here is that there’s nothing we can observe, in our Universe, that allows us to tell these three possibilities apart.” …

The observable Universe might be 46 billion light years in all directions from our point of view,
but there’s certainly more, unobservable Universe just like ours beyond that.
Image credit: Wikimedia Commons users Frédéric MICHEL and Azcolvin429, annotated by E. Siegel.

“The total amount of energy in all the particles and all the empty space in the Universe is somewhere around 10⁵⁴ kilograms, including dark matter and dark energy. But those numbers, while astronomical, are finite, and don’t give us any information about what happened in the Universe prior to the last tiny-fraction-of-a-second of inflation. We can do theoretical calculations to attempt to gain some insight, but they’re all model dependent. With the exception of a few specific models that would leave observable traces in our Universe (most don’t), we have no way of knowing how — or even if — the Universe got its start.” …

“The total amount of energy in all the particles and all the empty space in the Universe is somewhere around 10⁵⁴ kilograms, including dark matter and dark energy. But those numbers, while astronomical, are finite, and don’t give us any information about what happened in the Universe prior to the last tiny-fraction-of-a-second of inflation. We can do theoretical calculations to attempt to gain some insight, but they’re all model dependent. With the exception of a few specific models that would leave observable traces in our Universe (most don’t), we have no way of knowing how — or even if — the Universe got its start.” …

Read complete article in: 

Why science will never know everything about our Universe by Ethan Siegel at Medium.com 

according following notes of medium: 

[This post first appeared at Forbes, and is brought to you ad-free by our Patreon supporters.]

Ethan Siegel

Photo Credit: Photos are collected from author’s article.
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