String Theory: Worth the Wait or Just Stringing Us Along? (Part 2)

Author: Molly Kozminsky

Editors: Theresa Mau, Jimmy Brancho, and Alisha John

In my previous post, I discussed what string theory is, how it has not been experimentally verified, and how the existence of Higgs boson was proved fifty years after it was first proposed. In this post, I will continue to discuss the lengthy process of validating the theory of gravitational waves and where we stand with string theory research.

The Hundred-Year Quest for Gravitational Waves

If you think fifty years for verifying the existence of Higgs boson is a long wait, consider the case of gravitational waves. These waves, produced by accelerating objects with mass (e.g. stars and planets), cause perturbations in the fabric of space-time (the three space dimensions plus time) and could enable us to study some of physics’ unanswered questions, such as what happened during the moments after the Big Bang.

Albert Einstein first postulated gravitational waves in 1916, but even he changed his mind about whether or not they exist – twice. Ultimately though, many physicists were on board with the idea, and the hunt was on. One of the challenges in detecting gravitational waves is that they are very tiny, on the order of 10-18 meters. For reference, the wavelength of visible light is roughly 100 billion times longer. The signal of gravitational waves must therefore be detected with the most sensitive of sensors, but this also increases the possibility of detecting signals that aren’t the result of gravitational waves.

An early report of gravitational waves came in 1969, but those results could not be replicated. More recently, in 2014, there was another report from the BICEP2 telescope near the South Pole, but this signal was determined to be a false positive caused by cosmic dust.

 

screen-shot-2017-02-06-at-11-52-47-pm
Figure 1. LIGO, inside and out. The initial facility (which actually consists of two separate facilities to allow verification) has two perpendicular arms, each about 2.5 miles long, which are slightly elevated to remain level despite the curvature of the Earth. Using lasers and the most perfect mirrors ever made, incredibly small length changes in each of the arms caused by gravitational waves can be detected.

 

Then, on September 14, 2015, a chirp signaled that the investment had paid off. Evidence of gravitational waves emitted by the collision of two black holes was detected. On the human time scale, waiting from 1972, when the facility was first proposed, until the experimental verification in 2015 may seem like a long time (not to mention the wait from 1916 when gravitational waves were proposed), but on the cosmic scale, the wait was brief. The detected gravitational waves were emitted from a collision between two black holes that occurred about a billion years ago.

The facility that ultimately detected gravitational waves took eighteen years to go from idea to reality. In the beginning, even the researchers at the facility warned the National Science Foundation (NSF) that this facility would be extremely unlikely to detect gravitational waves, but they also stressed that the only way they could learn enough to create a functional system was to experiment with the technology available at the time. This was an incredible leap of faith on the part of the NSF, beginning with “Initial Laser Interferometer Gravitational-wave Observatory (LIGO)” in 1990 (a $272 million project) and then “Advanced LIGO”, a $200 million upgrade in 2010. The astronomical sum went towards creating and protecting the incredibly fine vacuum inside the arms as well as to create sufficiently sensitive detectors.

timeline
Figure 2. All in good time: check out the relative timelines for some of the research into gravitational waves (purple), the Higgs boson (light blue), and string theory (dark blue).

Making the Leap of Faith?

It took both patience and a tremendous amount of government funding to get from the theories behind the Higgs boson and gravitational waves to their experimental verification through the particle colliders and LIGO, raising the question of how to make the call when enough is enough. In the hunt for the Higgs boson, the US government sunk nearly $2 billion on the Superconducting Super Collider, which was ultimately canceled in part due to competition for funds with the International Space Station. Decisions are made based on both the priorities of people making the funding decisions and the demands to fund research with readily identifiable applications.

So where does this leave string theory? A major argument for basic research is that no one can predict all the applications of a scientific insight at the time of discovery or study, and string theory has already led to advances in mathematics and the study of black holes. While it may be easier to see how the results of biomedical research show up in our everyday life, the results from physics have shown up in various places like the development of the Internet, new materials, and medical imaging.

But while a lack of obvious applications should not preclude string theory research, there are additional problems. String theory research consumes a large fraction of funding for basic physics research as well as generally monopolizing paths that young scientists are able to take, impeding the development of alternative theories behind the mechanisms of the universe. In contrast, when the Higgs field needed experimental verification, other avenues were still pursued.

Some preliminary experimental tests have not verified the predictions of string theory, raising the question: How long do we keep funding research that remains in the theoretical realm? When do we declare a research path a dead end? The answers to these questions are likely to be answered on a case-by-case basis without hard and fast cut-off point. Still, funding decisions need to be made. This should challenge scientists to think critically about the weaknesses and potential pitfalls of their work to create a plan to overcome these obstacles.

In the case of string theory, the happiest ending may be a shift to applying its findings to math and physics rather than relying on it to provide all of the universe’s answers, while at the same time giving others room to explore alternative theories.

Scientists need the freedom and resources to grapple with big-picture challenges. Examples like the Higgs boson and gravitational waves have shown the rewards of patience and answering difficult questions often take time. Perhaps the biggest challenge is convincing ourselves that the results are worth the wait.

 

About the author

molly

Molly is a PhD student in Chemical Engineering at the University of Michigan. Her research involves the use of microfluidics (tiny channels) to isolate and study cancer cells traveling in the blood stream. Molly’s undergraduate degree is from MIT, and her master’s degree is from the University of Michigan. Outside of the lab, Molly enjoys reading, running, and optimizing her baking experiments.

Read all posts by Molly here.

 

Image Sources:

Figure 1: https://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/LIGO_schematic_%28multilang%29.svg/800px-LIGO_schematic_%28multilang%29.svg.png, https://www.flickr.com/photos/23925401@N06/24342686634

Figure 2: Molly Kozminsky

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