For centuries, scientists studied light to comprehend the visible world. Why are things colored? What is a rainbow? How do our eyes work? And what is light itself? These are questions that preoccupied scientists and philosophers since the time of Aristotle, including Roger Bacon, Isaac Newton, Michael Faraday, Thomas Young, and James Clerk Maxwell.
But in the late 19th century all that changed, and it was largely Maxwell’s doing. This was the period in which the whole focus of physics—then still emerging as a distinct scientific discipline—shifted from the visible to the invisible. Light itself was instrumental to that change. Not only were the components of light invisible “fields,” but light was revealed as merely a small slice of a rainbow extending far into the unseen.
Physics has never looked back. Today its theories and concepts are concerned largely with invisible entities: not only unseen force fields and insensible rays but particles too small to see even with the most advanced microscopes. We now know that our everyday perception grants us access to only a tiny fraction of reality. Telescopes responding to radio waves, infrared radiation, and X-rays have vastly expanded our view of the universe, while electron microscopes, X-ray beams, and other fine probes of nature’s granularity have unveiled the microworld hidden beyond our visual acuity. Theories at the speculative forefront of physics flesh out this unseen universe with parallel worlds and with mysterious entities named for their very invisibility: dark matter and dark energy.
This move beyond the visible has become a fundamental part of science’s narrative. But it’s a more complicated shift than we often appreciate. Making sense of what is unseen—of what lies “beyond the light”—has a much longer history in human experience. Before science had the means to explore that realm, we had to make do with stories that became enshrined in myth and folklore. Those stories aren’t banished as science advances; they are simply reinvented. Scientists working at the forefront of the invisible will always be confronted with gaps in knowledge, understanding, and experimental capability. In the face of those limits, they draw unconsciously on the imagery of the old stories. This is a necessary part of science, and these stories can sometimes suggest genuinely productive scientific ideas. But the danger is that we will start to believe them at face value, mistaking them for theories. (...)
Much the same consideration applies to the concept of “brane” (short for membrane) worlds. This arises from the most state-of-the-art variants of string theory, which attempt to explain all the known particles and forces in terms of ultra-tiny entities called strings, which can be envisioned as particles extended into little strands that vibrate. Most versions of the theory call for variables in the equations that seem to have the role of extra dimensions in space, so that string theory posits not four dimensions (of time and space) but 11. As physicist and writer Jim Baggott points out, “there is no experimental or observational basis for these assumptions”—the “extra dimensions” are just formal aspects of the equations. However, the latest versions of the theory suggest that these extra dimensions can be extremely large, constituting extra-dimensional branes that are potential repositories for alternative universes separated from our own like the stacked leaves of a book. Inevitably, there is an urge to imagine that these places too might be populated with sentient beings, although that’s optional. The point is that these brane worlds are nothing more than mathematical entities in speculative equations, incarnated, as it were, as invisible parallel universes.
Dark matter and dark energy are more directly motivated by observations of the real world. Dark matter is apparently needed to account for the gravitational effects that seem to come from parts of space where no ordinary matter is visible, or not enough to explain the tug. For example, rotating galaxies seem to have some additional source of gravitational attraction, beyond the visible stars and gas, that stops them from flying apart. The “lensing” effect where distant astrophysical objects get distorted by the gravitational warping of spacetime also seems to demand this invisible form of matter. But dark matter does not exist in the usual sense, in that it has not been seen and there are no theories that can convincingly explain or demand its existence. Dark energy too is a kind of “stuff” required to explain the acceleration of the universe’s expansion, discovered by astronomers observing far-away objects in the mid-1990s. But it is just a name for a puzzle, without any direct detection. (...)
Scientists, of course, are not just making things up, while leaning on the convenience of supposed invisibility. They are using dark matter and dark energy, and (if one is charitable) quantum many-worlds and branes, and other imperceptible and hypothetical realms, to perform an essential task: to plug gaps in their knowledge with notions they can grasp.
But in the late 19th century all that changed, and it was largely Maxwell’s doing. This was the period in which the whole focus of physics—then still emerging as a distinct scientific discipline—shifted from the visible to the invisible. Light itself was instrumental to that change. Not only were the components of light invisible “fields,” but light was revealed as merely a small slice of a rainbow extending far into the unseen.Physics has never looked back. Today its theories and concepts are concerned largely with invisible entities: not only unseen force fields and insensible rays but particles too small to see even with the most advanced microscopes. We now know that our everyday perception grants us access to only a tiny fraction of reality. Telescopes responding to radio waves, infrared radiation, and X-rays have vastly expanded our view of the universe, while electron microscopes, X-ray beams, and other fine probes of nature’s granularity have unveiled the microworld hidden beyond our visual acuity. Theories at the speculative forefront of physics flesh out this unseen universe with parallel worlds and with mysterious entities named for their very invisibility: dark matter and dark energy.
This move beyond the visible has become a fundamental part of science’s narrative. But it’s a more complicated shift than we often appreciate. Making sense of what is unseen—of what lies “beyond the light”—has a much longer history in human experience. Before science had the means to explore that realm, we had to make do with stories that became enshrined in myth and folklore. Those stories aren’t banished as science advances; they are simply reinvented. Scientists working at the forefront of the invisible will always be confronted with gaps in knowledge, understanding, and experimental capability. In the face of those limits, they draw unconsciously on the imagery of the old stories. This is a necessary part of science, and these stories can sometimes suggest genuinely productive scientific ideas. But the danger is that we will start to believe them at face value, mistaking them for theories. (...)
Much the same consideration applies to the concept of “brane” (short for membrane) worlds. This arises from the most state-of-the-art variants of string theory, which attempt to explain all the known particles and forces in terms of ultra-tiny entities called strings, which can be envisioned as particles extended into little strands that vibrate. Most versions of the theory call for variables in the equations that seem to have the role of extra dimensions in space, so that string theory posits not four dimensions (of time and space) but 11. As physicist and writer Jim Baggott points out, “there is no experimental or observational basis for these assumptions”—the “extra dimensions” are just formal aspects of the equations. However, the latest versions of the theory suggest that these extra dimensions can be extremely large, constituting extra-dimensional branes that are potential repositories for alternative universes separated from our own like the stacked leaves of a book. Inevitably, there is an urge to imagine that these places too might be populated with sentient beings, although that’s optional. The point is that these brane worlds are nothing more than mathematical entities in speculative equations, incarnated, as it were, as invisible parallel universes.
Dark matter and dark energy are more directly motivated by observations of the real world. Dark matter is apparently needed to account for the gravitational effects that seem to come from parts of space where no ordinary matter is visible, or not enough to explain the tug. For example, rotating galaxies seem to have some additional source of gravitational attraction, beyond the visible stars and gas, that stops them from flying apart. The “lensing” effect where distant astrophysical objects get distorted by the gravitational warping of spacetime also seems to demand this invisible form of matter. But dark matter does not exist in the usual sense, in that it has not been seen and there are no theories that can convincingly explain or demand its existence. Dark energy too is a kind of “stuff” required to explain the acceleration of the universe’s expansion, discovered by astronomers observing far-away objects in the mid-1990s. But it is just a name for a puzzle, without any direct detection. (...)
Scientists, of course, are not just making things up, while leaning on the convenience of supposed invisibility. They are using dark matter and dark energy, and (if one is charitable) quantum many-worlds and branes, and other imperceptible and hypothetical realms, to perform an essential task: to plug gaps in their knowledge with notions they can grasp.
by Philip Ball, Nautilus | Read more:
Image: Miko Maciaszek 
