Question Why the universe looks the same irrespective direction and position?

Apr 17, 2021
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According to Friedman, the universe looks the same irrespective of direction and position. But I don't get it.
 
Mar 4, 2020
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I'm not sure what characteristics he or you are referring to. I'm going to assume it's the distribution of mass. Maybe temperature. Not only is it the same, but the farther out one looks, the denser it gets. Something is out of kilter. Something is senseless. It's always been hard for me to think of astronomy as a science. No solid foundation. Everything is indirect, and usually wrong. Like elliptical orbits.
 
Jan 27, 2020
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I'm not sure what characteristics he or you are referring to. I'm going to assume it's the distribution of mass. Maybe temperature. Not only is it the same, but the farther out one looks, the denser it gets. Something is out of kilter. Something is senseless. It's always been hard for me to think of astronomy as a science. No solid foundation. Everything is indirect, and usually wrong. Like elliptical orbits.

The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' And the Standard Model of Cosmology also relies on the fundamental assumption that we don’t occupy a special place in the Universe, an idea known as the Copernican Principle*.

This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this says that "the Universe is knowable and is playing fair with scientists."

In a perfectly homogeneous and isotropic Universe the CMB would look likewise perfectly homogeneous and isotropic. However, during the very early phases of the Universe history (particularly, during a period known as inflation), this otherwise slightly boring picture was spiced up a bit and small perturbations were created in this smooth landscape in the form of curvature fluctuations. These incidentally, went on to form all the structure we know today – galaxies, clusters of galaxies, etc., and are the reason why we can exist today and discuss anisotropy! These perturbations can be studied by analysing the tiny temperature and polarization differences that were imprinted in the CMB as a result, which are represented as colored blots in the CMB map below. They are really tiny perturbations: 1 part in 100,000. As far as we can see, large-scale isotropy is at least, a very good approximation. As far as homogeneity is concerned, we can only comment on the portion of the Universe we see, but here large-scale homogeneity certainly seems to also hold.

CMB planck.jpg
The Cosmic Microwave Background (CMB) as seen by the Planck satellite. Credits: ESA and the Planck Collaboration.

In the standard picture, only these tiny fluctuations generated during inflation leave their imprint on the CMB. A distinctive feature is that some randomness is involved in their generation; their statistical behaviour is constrained by physics, but what exact perturbation will appear at a precise spot is random. If we were to make an analogy with a coin toss, we could say that physics chooses the coin, but the particular outcome of a toss is then random.

Looking out into the night sky, we see a clumpy universe: planets orbit stars in solar systems and stars are grouped into galaxies, which in turn form enormous galaxy clusters. But cosmologists assume this effect is only local: that if we look on sufficiently large scales, the universe is actually uniform.

The vast majority of calculations made about our universe start with this assumption: that the universe is broadly the same, whatever your position and in whichever direction you look.

If, however, the universe was stretching preferentially in one direction, or spinning about an axis in a similar way to the Earth rotating, this fundamental assumption, and all the calculations that hinge on it, would be wrong.

Now, scientists from University College London and Imperial College London have put this assumption through its most stringent test yet and found only a 1 in 121,000 chance that the universe is not the same in all directions.

To do this, they used maps of the cosmic microwave background (CMB) radiation: the oldest light in the universe created shortly after the Big Bang. The maps were produced using measurements of the CMB taken between 2009 and 2013 by the European Space Agency's Planck satellite, providing a picture of the intensity and, for the first time, polarisation (in essence, the orientation) of the CMB across the whole sky.

4 CMB's.jpg
Four potential CMB patterns for universes with direction

Previously, scientists had looked for patterns in the CMB map that might hint at a rotating universe. The new study considered the widest possible range of universes with preferred directions or spins and determined what patterns these would create in the CMB.

A universe spinning about an axis, for example, would create spiral patterns, whereas a universe expanding at different speeds along different axes would create elongated hot and cold spots.

Dr Stephen Feeney, from the Department of Physics at Imperial, worked with a team led by Daniela Saadeh at University College London to search for these patterns in the observed CMB. The results, published recently in the journal Physical Review Letters, show that none were a match, and that the universe is most likely directionless.

Daniela Saadeh from University College London added: "You can never rule it out completely, but we now calculate the odds that the universe prefers one direction over another at just 1 in 121,000. We're very glad that our work vindicates what most cosmologists assume. For now, cosmology is safe."

See: http://www.earlyuniverse.org/does-the-universe-look-the-same-in-all-directions/

See: https://earthsky.org/space/our-universe-has-no-direction

See: https://universeadventure.org/big_bang/expand-balance.htm#:~:text=In the image on the left, the universe,look around, the universe will be the same.

See: https://phys.org/news/2016-09-scientists-universe.html

* The Copernican Principle is a basic statement in physics that there should be no ``special'' observers. For example, the Aristotelian model of the solar system in the Middle Ages placed the Earth at the center of the solar system, a unique place since it ``appears'' that everything revolved around the Earth. Nicolaus Copernicus demonstrated that this view was incorrect and that the Sun was at the center of the solar system with the Earth in orbit around the Sun.

The implications of Copernicus' work can not be exaggerated. His views challenged the literal interpretation of Scripture, the philosophical and metaphysical foundations of moral theory, and even common sense itself. The result was a massive opposition to his reported ideas. It was the slow, sure acceptance of the heliocentric theory by natural philosophers that ultimately quieted the general clamor, however the name of Copernicus is still a battle cry against the establishment in religion, philosophy and science. In later years with Freud, man lost his Godlike mind; with Darwin his exalted place among the creatures of the Earth; with Copernicus man had lost his privileged position in the Universe.

The lesson learned by future scientists is that if a theory requires a special origin or a particular viewpoint in order to work, then it is not plausible.

See: abyss.oregon.edu

The contributions of the Planck Satellite and the COBE, Cosmic Background Explorer, combined with the Hubble Ultra Deep Field** (where every dot and squiggle of light is a distant and therefore early galaxy), must be applauded for providing scientists and astrophysicists with the data and images necessary to show that the universe, on the largest scales imaginable, is isotropic. The sheer size and majesty of our universe is daunting but understandable and every article is a building block in our quest for knowledge.
Hartmann352

** hubble ultra deep field.jpg
 

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