The Trouble With Physics by Lee Smolin

Author:Lee Smolin
Language: eng
Format: epub
Publisher: Houghton Mifflin Harcourt

The existence of such a cutoff would be puzzling from the point of view of the most widely accepted theory of the very early universe, which is inflation. According to the theory of inflation, the universe expanded exponentially fast during one extremely early period. Inflation accounts for the observation that the cosmic background radiation is so nearly uniform. It does this by ensuring that all the parts of the universe we see now could have been in causal contact when the universe was still a plasma.

The theory also predicts the fluctuations in the cosmic microwave background, which are hypothesized to be remnants of quantum effects during the period of inflation. The uncertainty principle implies that the fields dominating the energy of the universe during inflation fluctuate, and these fluctuations become imprinted on the geometry of space. As the universe expands exponentially, they persist, causing fluctuations in the temperature of the radiation produced when the universe becomes transparent.

Inflation is believed to have produced a huge region of the universe with relatively uniform properties. This region is thought to be many orders of magnitude larger than the observable region, because of a simple argument about scales. If inflation had stopped just at the point where it created a region as large as we now observe, there must have been some parameter in the physics of inflation that selected a special time to stop, which just happens to be our era. But this seems improbable, because inflation took place when the universe had a temperature ten to twenty orders of magnitude greater than the center of the hottest star today; thus the laws governing it must have been different laws, which dominated physics only in those extreme conditions. There are many hypotheses about the laws that governed inflation, and none of them say anything about a time scale of 10 billion years. Another way to put this is that there seems no way for the present value of the cosmological constant to have anything to do with the physics that caused inflation.

Thus if inflation produced a uniform universe on the scale that we observe, it likely produced a universe that is uniform on much larger scales. This in turn implies that the pattern of fluctuations produced by inflation should go on and on, no matter how far you look. If you could see beyond the present size of the observable universe, you should continue to see small fluctuations in the cosmic microwave background. Instead, the data hint that the fluctuations may cease above the scale R.

Indeed, as cosmologists have examined the large-scale modes in the microwave background, they have found more mysteries. It’s an item of faith among cosmologists that at the largest scales the universe should be symmetric—that is, any one direction should be like any other. This is not what is seen. The radiation in these large-scale modes is not symmetric; there is a preferred direction. (It has been called the “axis of evil” by the cosmologists Kate Land and João Magueijo.

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