The testing of hypotheses and theoretical predictions is such an integral part of science that we really have to question any theory that cannot be tested. If a scientific theory cannot be tested, is it really a scientific theory at all? Is it good enough that experimental tests may be possible in the distant future? We may not be able to provide definite answers to these questions, but such questions should be and are being asked.
The twentieth century was a very exciting time for physicists. The decades of the 1920s and 1930s were especially fruitful in revealing the inner workings of nature. For a generation or two, radical new theories were proposed and tested in quick succession. Every few years, the scientific world was forced to rethink its picture of the world at a very fundamental level. Theorists worked closely with experimentalists to prove the theories that worked and discard the erroneous ones.
The reverberations of the quantum revolution fed even more progress in the decades after World War II. As quantum physics became better and more widely understood, technological advances helped verify its claims and extend its reach, even as the theory led to further improvements in technology. Larger and more sophisticated particle accelerators, faster computers, and more sensitive detectors all helped fill in a standard model for the fundamental particles and interactions.
In the last few decades, at the most fundamental level of understanding, many theoretical physicists feel that progress has slowed down considerably. What’s more, most of the serious proposals for incorporating gravity into a quantum framework cannot be tested with any experimental tools we can imagine building in the near (or even distant) future. In this context, it is unclear whether the next generation of particle accelerators is even worth building.
QUANTUM LEAP
The world’s first particle accelerator, the cyclotron developed by Ernest Lawrence in 1932, is reputed to have cost a mere $25. By contrast, the Large Hadron Collider, where the Higgs boson was detected, cost more than $5 billion!
Indeed, much of the hope for “experimental” testing of the most basic theories currently rests not in improved atom smashers but in cosmology and observational astronomy. We seem to be approaching the point where only one experiment can be performed to verify the claims of a “theory of everything,” and that experiment has actually been going on for about 15 billion years. It is the universe itself, the Big Bang and the subsequent evolution of matter and energy in all of its forms, obeying a certain set of rules, some of which we know, and others we have yet to discover.
It may be that the structure of quantum field theory, so successful at describing the behavior of quarks and leptons when we can ignore gravity, has reached the limits of its capacity to describe the universe—much as classical physics petered out a little over a century ago. Perhaps we need another revolution to overthrow the current, accepted framework. Is quantum physics destined to be overturned and replaced by a new theory that we cannot yet imagine?
The next Einstein, Planck, or Schroedinger may already be among us, desperately trying alternative formulations that will conceptually unite gravity with the other forces, explain why we have our assortment of fundamental particles and what all of their properties (including mass) has to be.
QUANTUM QUOTE
I still believe there are grounds for cautious optimism that we may now be near the end of the search for the ultimate laws of nature.
—Stephen Hawking, from A Brief History of Time
Based on our history, especially our experience just before the quantum revolution—the last time that reputable scientists declared the end of physics—most physicists believe that there is still much progress to come. The odds are good that the story of physics is not finished yet. If and when the end of quantum physics does come, whatever comes next will probably be even more bizarre than quantum physics, but ultimately more rewarding.
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