March 15th, 2019
(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: firstname.lastname@example.org
“The most incomprehensible thing about the universe is that it is comprehensible, ”Albert Einstein famously once said. These days, however, it is far from being a matter of consensus that the universe is comprehensible, or even that it is unique. Fundamental physics is facing a crisis, related to two popular concepts that are frequently invoked, summarized tellingly by the buzzwords “multiverse” and “uglyverse.”
…With the advent of the multiverse, this has changed: As unlikely as a coincidence may appear, in the zillions of universes that compose the multiverse, it will exist somewhere. And if the coincidence seems to favor the emergence of complex structures, life or consciousness, we shouldn’t even be surprised to find ourselves in a universe that allows us to exist in the first place. But this “anthropic reasoning” in turn implies that we can’t predict anything anymore. There is no obvious guiding principle for the CERN physicists searching for new particles. And there is no fundamental law to be discovered behind the accidental properties of the universe.
Quite different but not less dangerous is the other challenge—the “uglyverse”: According to theoretical physicist Sabine Hossenfelder, modern physics has been led astray by its bias for “beauty,” giving rise to mathematically elegant, speculative fantasies without any contact to experiment. Physics has been “lost in math,” she argues. But then, what physicists call “beauty” are structures and symmetries. If we can’t rely on such concepts anymore, the difference between comprehension and a mere fit to experimental data will be blurred.
…To appreciate this point one needs to understand the principle behind both quantum measurements and “spooky action at a distance.” Instrumental for both phenomena is a concept known as “entanglement,” pointed out in 1935 by Einstein, Boris Podolsky and Nathaniel Rosen: In quantum mechanics, a system of two entangled spins adding up to zero can be composed of a superposition of pairs of spins with opposite directions while it is absolutely undetermined in which direction the individual spin points. Entanglement is nature‘s way of integrating parts into a whole; individual properties of constituents cease to exist for the benefit of a strongly correlated total system.
Whenever a quantum system is measured or coupled to its environment, entanglement plays a crucial role: Quantum system, observer and the rest of the universe become interwoven with each other. From the perspective of the local observer, information is dispersed into the unknown environment and a process called “decoherence”—first discovered by H. Dieter Zeh in 1970—sets in. Decoherence is the agent of classicality: It describes the loss of quantum properties when a quantum system interacts with its surroundings. Decoherence acts if it would open a zipper between quantum physics’ parallel realities. From the observer’s perspective, the universe and she herself seem to “split” into separated Everett branches. The observer observes a live cat or a dead cat but nothing in between. The world looks classical for her, while from a global perspective it is still quantum mechanical. In fact, in this view the entire universe is a quantum object.
…Moreover, this conclusion extends to other multiverse concepts such as different laws of physics in the various valleys of the “string theory landscape” or other “baby universes” popping up in eternal cosmological inflation. Since entanglement is universal, it doesn’t stop at the boundary of our cosmic patch. Whatever multiverse you have, when you adopt quantum monism they are all part of an integrated whole: There always is a more fundamental layer of reality underlying the many universes within the multiverse, and that layer is unique.