Modern Cosmology Theories. Big Bang or Big Bounce?

1. _______ Atoms are now such a commonplace idea that it is hard to remember how radical they used to seem. When scientists first hypothesized atoms centuries ago, many questioned whether the concept of atoms could even be called scientific. Gradually, however, evidence for atoms accumulated and reached the tipping point with Albert Einstein’s 1905 analysis of Brownian movement, the random jittering of dust grains in a fluid. Even then, it took another twenty years for physicists to develop a theory explaining atoms – namely, quantum mechanics – and another 30 years for physicist Erwin Mueller to make the first microscopic images of them.

2. ____ Physicists’ understanding of the composition of space and time is following a similar path, but several steps behind. Just as the behavior of materials indicates that they consist of atoms, the behavior of space and time suggests they, too, have some fine-scale structure – either a mosaic of spacetime ‘atoms” or some other filigree work. Similarly to material atoms, the space atoms are the smallest indivisible units of distance. They are generally thought to be about 10^{-35 meter in size, far too tiny to be seen by today’s most powerful instruments, which probe distances as short as 10 -18 meter. Consequently, many scientists question whether the concept of atomic spacetime can even be called scientific. Undeterred, other researchers are coming up with possible ways to detect such atoms indirectly.}

3. ______ The most promising involve observations of the cosmos. If we imagine rewinding the expansion of the universe back in time, the galaxies we see all seem to converge on a single infinitesimal point: the big bang singularity. At this point our current theory of gravity – Einstein’s general theory of relativity –  predicts that the universe had an infinite density and temperature. This moment is sometimes sold as the beginning of the universe, the birth of matter, space and time. Such an interpretation, however, goes too far. To explain what really happened at the big bang, physicists must transcend relativity, we must develop a theory of quantum gravity, which would capture the fine structure of spacetime to which relativity is blind.

4._____ The details of that structure came into play under dense conditions of the primordial universe, and traces of it may survive in the present-day arrangements of matter and radiation. In short, if spacetime atoms exist, it will not take centuries to find evidence, as it did for material atoms. With some luck, we may know within the coming decade.

5.____ Physicists have devised several theories of quantum gravity, each applying quantum principles in a distinct way. The theory of loop quantum gravity (“loop gravity”, for short) was developed using a two-step procedure. First, theorists mathematically reformulated general relativity to resemble the classical theory of electromagnetism: eponymous “loops” of the theory are analogous of electric and magnetic lines. Second, following innovative procedures, some that are akin to the mathematics of knots they applied quantum principles to the loops. The resulting quantum gravity theory predicts the existence of spacetime atoms.

6.____ Other approaches, such as string theory and so-called causal dynamical triangulations, do not predict spacetime atoms per se but suggest other ways that sufficiently short distances might be indivisible. The differences among these theories have given rise to controversy, but the theories are perhaps not contradictory so much as complementary.

7. ____ The theory’s power is its ability to capture the fluidity of spacetime. Einstein’s great insight was that spacetime is no mere stage at which the drama of the universe unfolds. It is an actor in its own right. It not only determines the motion of bodies within the universe, but it evolves. A complicated interplay between matter and spacetime ensues. Space can grow and shrink.

 

12. Fill the gaps with the words:

a) equation      b) hypothesis           c) law     d) principle                e) theory

Physics timeline

1787  Charles’s … (1) relating the pressure, volume, and temperature of a gas was established by Jacques Charles.

1811  Avogadro’s … (2) relating volumes and numbers of molecules of gases was proposed by Amedeo Avogadro.

1904 The … (3) of radioactivity was put forward by Ernst Rutherford and Frederick Soddy.

1926   Wave mechanics was introduced by Erwin Schrödinger. Schrödinger (1887-1961) is an Austrian-born Irish physicist and philosopher of science who shared with Paul Dirac the 1933 Nobel prize for physics for his elucidation of the Schrödinger wave …(4) which is of fundamental importance in studies of quantum mechanics.

1927 The uncertainty… (5) of quantum physics was established by Werner Heisenberg.

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