In research published in November in the Astrophysical Journal , the scientists report tiny discrepancies in the orbital speeds of distant stars that they think reveals a faint gravitational effect — and one that could put an end to the prevailing ideas of dark matter. The study suggests an incomplete scientific understanding of gravity is behind what appears to be the gravitational strength of galaxies and galaxy clusters, rather than vast clouds of dark matter.
That might mean pure mathematics, and not invisible matter, could explain why galaxies behave as they do, said study co-author Stacy McGaugh, who heads the astronomy department at Case Western Reserve University in Cleveland.
Astronomers long assumed that stars orbited the centers of galaxies at speeds predicted by the theory of gravity formulated by the English physicist and mathematician Isaac Newton more than years ago. Newton based his theory that objects attract each other with a force varying according to their mass on observations of the orbits of the planets.
With refinements from the theories of the German-born physicist Albert Einstein in the 20th century, it remains astonishingly accurate. The Big Bang was not an explosion IN space. It was a process that involved ALL of space. This misconception causes more confusion than any other in cosmology. Unfortunately, many students, teachers, and scientists! In reality, ALL of space was filled with energy right from the beginning. There was no center to the expansion, and no magical point from which matter hurtled outward.
But that primordial pellet of matter and energy was NOT surrounded by empty space In fact, if the whole universe is infinitely large now, then it was always infinite, including during the Big Bang as well. Thus the Big Bang took place everywhere in space, not at a particular point in space. For much of the twentieth century, astronomers and physicists believed that space might NOT be infinitely large - that is, space might actually curve around on itself to form a "closed universe.
The shape was later favored by Einstein as a possible shape for the universe. Such a closed universe would have a finite volume, yet no boundaries or edges. Although closed universes cannot be visualized from the outside, they CAN be visualized from the inside. For example, the image at right gives an idea of what a tiny closed universe might look like. In a real closed universe, you cannot see the back of your head, the way you can here. If you shrink such a space down, then everything in it gets closer together, and the volume of the closed universe gets closer and closer to zero.
Current evidence shows that our part of the universe appears not to be curved. This tells us that either the universe is infinitely large, or else is so large that we cannot detect its curvature from the tiny portion we can observe -- just as we could not tell that the Earth was curved if our measurements were confined to a sandbox!
A large enough clump of matter will collapse to form a black hole, but ONLY if it is surrounded by relatively empty space. During the Big Bang, there WAS NO empty space: ALL of space was filled more or less uniformly with matter and energy; there was no "center of attraction" around which matter could coalesce. Under these circumstances, a cosmic-scale black hole will not form and lucky for us! Because it takes time for light from distant objects to reach us.
We see the sun as it looked about 8 minutes ago Current studies of distant exploding stars have led astronomers to conclude that the universe is not only expanding - the expansion may be accelerating with time. This is not due to an "anti-gravity force" but rather to gravity itself. In fact, the effect was predicted as a possibility on the basis of Einstein's theory of gravity. It may seem strange that gravity can be "repulsive" as well as attractive.
The secret is that the expansion applies to the fabric of space itself - not to the matter within it; space behaves very differently from matter. For example, no chunk of matter can travel through space at the speed of light. Similarly, while matter is attracted to other matter by gravity, space behaves differently: Space can either expand or contract as a consequence of gravity.
When they say "the universe is expanding," what exactly is expanding? As bizarre as it may seem, space itself is expanding - specifically, the vast regions of space between galaxies. But if you can't see space, or feel it or touch it - how can it be expanding? When hyper-massive black holes collide, the impact creates a huge release of energy in the form of gravitational waves. When giant black holes finally evaporate, they release a huge amount of energy in the form of low-frequency photons.
Penrose has been working with Polish, Korean and Armenian cosmologists to see if these patterns can actually be found by comparing measurements of the CMB with thousands of random patterns. It is unlikely that we will ever be able to directly observe what happened in the first moments after the Big Bang, let alone the moments before.
The opaque superheated plasma that existed in the early moments will likely forever obscure our view. But there are other potentially observable phenomena such as primordial gravitational waves, primordial black holes, right-handed neutrinos, that could provide us some clues about which of the theories about our universe are correct. Until then, the story of our universe, its beginnings and whether it has an end, will continue to be debated.
Join one million Future fans by liking us on Facebook , or follow us on Twitter or Instagram. If you liked this story, sign up for the weekly bbc. What if the Universe has no end? Share using Email. By Patchen Barss 20th January The Big Bang is widely accepted as being the beginning of everything we see around us, but other theories that are gathering support among scientists are suggesting otherwise. The usual story of the Universe has a beginning, middle, and an end.
Our observable universe expanded from one tiny homogenous region within that primordial hot mess. Around the BBC.
The no-boundary proposal has fascinated and inspired physicists for nearly four decades. The proposal represented a first guess at the quantum description of the cosmos — the wave function of the universe. The proposal is, of course, only viable if a universe that curves out of a dimensionless point in the way Hartle and Hawking imagined naturally grows into a universe like ours. Hawking and Hartle argued that indeed it would — that universes with no boundaries will tend to be huge, breathtakingly smooth, impressively flat, and expanding, just like the actual cosmos.
The paper ignited a controversy. After two years of sparring, the groups have traced their technical disagreement to differing beliefs about how nature works. Hartle and Hawking saw a lot of each other from the s on, typically when they met in Cambridge for long periods of collaboration. In , Albert Einstein discovered that concentrations of matter or energy warp the fabric of space-time, causing gravity.
Hawking and Hartle were thus led to ponder the possibility that the universe began as pure space, rather than dynamical space-time. And this led them to the shuttlecock geometry. In the s, Feynman devised a scheme for calculating the most likely outcomes of quantum mechanical events. To predict, say, the likeliest outcomes of a particle collision, Feynman found that you could sum up all possible paths that the colliding particles could take, weighting straightforward paths more than convoluted ones in the sum.
Likewise, Hartle and Hawking expressed the wave function of the universe — which describes its likely states — as the sum of all possible ways that it might have smoothly expanded from a point. If the weighted sum of all possible expansion histories yields some other kind of universe as the likeliest outcome, the no-boundary proposal fails.
The problem is that the path integral over all possible expansion histories is far too complicated to calculate exactly. Countless different shapes and sizes of universes are possible, and each can be a messy affair. Even the minisuperspace calculation is hard to solve exactly, but physicists know there are two possible expansion histories that potentially dominate the calculation.
These rival universe shapes anchor the two sides of the current debate. Weirder expansion histories, like football-shaped universes or caterpillar-like ones, mostly cancel out in the quantum calculation.
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