Physics of the Expanding Universe

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Electrodynamics in the Expanding Universe | Progress of Theoretical Physics | Oxford Academic

The team uses the supernovae explosions of white dwarf stars as standard beacons to measure distances far out into the swelling universe; they calibrate the brightness of nearby supernovae by monitoring variable stars, called cepheids, in the same galaxies. Theorists, salivating at the possibility, have begun to dream up hidden ingredients in the early universe—new particles or interactions—that could patch over the gulf.

With stakes that high, astronomers put their heads together in Santa Barbara to double and triple check the SH0ES result against other ways to measure the constant. A team called H0LiCOW relied on gravitational lenses, freak cosmic alignments where the light from a very distant, flickering beacon called a quasar is bent into multiple images on the sky by the gravity of another, intervening galaxy.

Each image is formed by light traveling along a different path across expanding space. One point for possible new physics. But the meeting brought a twist. Instead, her team looked toward old, swollen stars called red giants. These stars have already exhausted the hydrogen fuel at their hearts, converting it to a core of helium that sits, inert, as a hydrogen shell around the core continues to burn. The star, seen from afar, grows brighter and brighter. But at a certain, predictable limit the temperature and pressure in the core grow high enough to burn helium, too, generating an explosive flash of energy that rearranges the interior of the star, ultimately causing it to begin to dim.

By finding the very brightest red giants in a distant galaxy—the ones that toe this theoretical limit—the team could use them as standard candles to calculate distances and its own H0. Stranger still, at the end of the s came the realization that the universe is expanding. This realization came only after an uphill battle. Einstein expressed the general opinion in after de Sitter produced equations that could describe a universe that was expanding, a universe with a beginning. Einstein wrote him that "This circumstance irritates me.

In his gravitational field equations, Einstein was just then providing a compact mathematical tool that could describe the general configuration of matter and space taking the universe as a whole. The peculiar curvature of space predicted in the equations was quickly endorsed in famous experiments, and by the early s most leading scietists agreed that Einstein's field equations could make a foundation for cosmology. I have erected but a lofty castle in the air So let us be satisfied and not expect an answer, and rather see each other again as soon as possible!

EXIT to read more about Einstein's general theory and the observations that made it famous. Einstein's first try at a model likewise could not contain matter and be stable.

For the equations showed that if the universe was static at the outset, the gravitational attraction of the matter would make it all collapse in upon itself. That seemed ridiculous, for there was no reason to suppose that space was so unstable. E instein found he could stabilize his model by adding a simple constant term to the equations. If this constant was not zero, the model would not have to collapse under its own gravity.

To Build a Distance Ladder

This "cosmological constant," Einstein admitted, was only "a hypothetical term. The introduction of such a constant implies a considerable renunciation of the logical simplicity of the theory Since I introduced this term, I had always a bad conscience I am unable to believe that such an ugly thing should be realized in nature.

Vesto Slipher. How Slipher could measure velocities in the heavens.

Do We Expand With The Universe?

Spiral Nebula in Ursa Major M. T he powerful belief in a static universe could only be overturned by the weight of accumulating observations. The first of these observations had already been reported in Probably the observation was unknown to Einstein when he was developing his theory and corresponding with de Sitter. World War I had disrupted communications between the English-speaking nations and Germany, where Einstein worked, while de Sitter had only a second-hand, incomplete report of the crucial observation.

Cosmic showstopper

The observation had been made at the Lowell Observatory in Arizona. Its founder, Percival Lowell, suspected that spectral lines seen in the light from one species of nebula, the "planetary" nebulae, might also be found in the spectra of spiral nebulae.

In Lowell asked his assistant Vesto Slipher to get spectra of spiral nebulae. Slipher initially doubted that it could be done. W ith a new camera, its speed increased by a factor of 30, on the night of 17 September Slipher obtained a spectrogram for the Andromeda Nebula. The spectrogram indicated that the nebula was approaching the solar system at an amazingly high velocity. Slipher made more observations, exposing the same photographic plate over multiple nights for example, 29, 30, and 31 December That was so large that some astronomers did not believe it possible.

Over the next two years, Slipher measured velocities for other spiral nebulae. The first few measurements revealed approaching nebulae on the south side of our galaxy and receding nebulae on the opposite side. Slipher formed a "drift" hypothesis. He thought that it was our galaxy that was moving relative to the nebulae, toward the south and away from the north.

However, observations of more spirals contradicted this. Receding spirals were found on the south side of our galaxy as well as on the north side. Slipher nevertheless clung to his drift hypothesis. Perhaps more observations, he argued, would find at least a preponderance of approaching nebulae on the south side, toward which he thought our galaxy was moving. A different interpretation of the velocities seen in spiral nebulae soon turned up. De Sitter's model of a static universe had a diminishing frequency of light vibrations with increasing distance.

Perhaps distant objects were not really receding at great speeds, but were only emitting a different frequency of light.

Cosmologists Debate How Fast the Universe Is Expanding

Nothing like that happened in Einstein's model of a static universe, so Slipher's measurements might give a way to choose between the two models. World War I had slowed communications, but by de Sitter knew of Slipher's velocity measurements for 25 spiral nebulae. Only 3 were approaching.