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Stephen Hawking at 70

January 7, 2012 Leave a comment

What does he think about all day? (Image: Science Museum/Sarah Lee)

When he was diagnosed with motor neurone disease aged just 21, Stephen Hawking was only expected to live a few years. He will be 70 this month, and in an exclusive interview with New Scientist he looks back on his life and work

 Read more: Hawking highlights

STEPHEN HAWKING is one of the world’s greatest physicists, famous for his work on black holes. His condition means that he can now only communicate by twitching his cheek (see “The man who saves Stephen Hawking’s voice“). His responses to the questions are followed by our own (New Science, “NS”) elaboration of the concepts he describes.

 What has been the most exciting development in physics during the course of your career?

COBE’s discovery of tiny variations in the temperature of the cosmic microwave background and the subsequent confirmation by WMAP that these are in excellent agreement with the predictions of inflation. The Planck satellite may detect the imprint of the gravitational waves predicted by inflation. This would be quantum gravity written across the sky.

New Scientist writes: The COBE and WMAP satellites measured the cosmic microwave background (CMB), the afterglow of the big bang that pervades all of space. Its temperature is almost completely uniform – a big boost to the theory of inflation, which predicts that the universe underwent a period of breakneck expansion shortly after the big bang that would have evened out its wrinkles.

If inflation did happen, it should have sent ripples through space-time – gravitational waves – that would cause variations in the CMB too subtle to have been spotted so far. The Planck satellite, the European Space Agency’s mission to study the CMB even more precisely, could well see them.

Einstein referred to the cosmological constant as his “biggest blunder”. What was yours?

I used to think that information was destroyed in black holes. But the AdS/CFT correspondence led me to change my mind. This was my biggest blunder, or at least my biggest blunder in science.

NS: Black holes consume everything, including information that strays too close. But in 1975, together with the Israeli physicist Jakob Bekenstein, Hawking showed that black holes slowly emit radiation, causing them to evaporate and eventually disappear. So what happens to the information they swallow? Hawking argued for decades that it was destroyed – a major challenge to ideas of continuity, and cause and effect. In 1997, however, theorist Juan Maldacena developed a mathematical shortcut, the “Anti-de-Sitter/conformal field theory correspondence”, or AdS/CFT. This links events within a contorted space-time geometry, such as in a black hole, with simpler physics at that space’s boundary.

In 2004, Hawking used this to show how a black hole’s information leaks back into our universe through quantum-mechanical perturbations at its boundary, or event horizon. The recantation cost Hawking a bet made with fellow theorist John Preskill a decade earlier.

What discovery would do most to revolutionize our understanding of the universe?

The discovery of supersymmetric partners for the known fundamental particles, perhaps at the Large Hadron Collider. This would be strong evidence in favour of M-theory.

NS: The search for supersymmetric particles is a major goal of the LHC at CERN. The standard model of particle physics would be completed by finding the Higgs boson, but has a number of problems that would be solved if all known elementary particles had a heavier “superpartner”. Evidence of supersymmetry would support M-theory, the 11-dimensional version of string theory that is the best stab so far at a “theory of everything“, uniting gravity with the other forces of nature.

If you were a young physicist just starting out today, what would you study?

I would have a new idea that would open up a new field.

What do you think most about during the day?

Women. They are a complete mystery.

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To mark Hawking’s birthday, the Centre for Theoretical Cosmology, University of Cambridge, is hosting a symposium entitled “The State of the Universe” on 8 January (watch live at ctc.cam.ac.uk/hawking70/multimedia.html). An exhibition of his life and work opens at the Science Museum, London, on 20 January

Variable Dark Energy Could Explain Old Galaxy Clusters

January 6, 2012 Leave a comment
[Re-Print Alert: Original Here]

by Ken Croswell and Maggie McKee 

Does dark energy change over time? An alternative model of the as yet undetected entity that is thought to be accelerating the universe’s expansion could explain some puzzling observations of galaxy clusters. But it will have to jump many more hurdles to compete with the simplest and so far most successful model of the elusive entity.

That model, called the cosmological constant, holds that there is a certain amount of repulsive energy in every cubic centimeter of space, and that amount stays the same over time. As the universe expands, more space exists, and so the expansion accelerates.

Now Edoardo Carlesi of the Autonomous University in Madrid, Spain, and his colleagues have simulated a universe where the amount of repulsive energy per unit of volume changes with time.

They say the model can explain how several galaxy clusters grew to weigh as much as a quadrillion (1015) suns by the time the universe was just 6 billion years old. That’s a puzzle because some researchers say 6 billion years would not have been enough time for gravity to amass such large structures.

 

Standard recipe

The puzzle arises if the standard “recipe” for the universe is used. The ingredients for that recipe are a large amount of dark energy, in the form of a cosmological constant, and a dollop of matter. Their ratio has been calculated by studying the cosmic microwave background, radiation that reveals the distribution of matter and energy in the early universe.

Looking at the cosmic microwave background data through the lens of a different dark energy model can produce different ratios of ingredients. The cosmological constant model allows for matter to make up 27 per cent of the universe’s energy density, whereas the dark energy model studied by Carlesi’s team provides a more generous helping: 39 per cent.

Massive clusters can form up to 10 times as often using this recipe, the researchers say. “You can explain current observations within a model that allows much more matter,” says Carlesi. As a result, galaxies attract other galaxies through their gravitational pull, so massive clusters form faster.

First hurdle

The cluster problem may not even be a problem, though, says Dragan Huterer at the University of Michigan in Ann Arbor. He says the jury is still out on whether the clusters challenge the leading cosmological model, because there is a lot of uncertainty about their mass, most of which is thought to be tied up in invisible dark matter.

The cosmological constant has so far been able to explain a wide range of observations, so turning to a relatively unproven model to account for a few galaxy clusters that may be heavier than expected “is like using a huge hammer to kill a tiny fly”, he says.

Carlesi says this is just the first test of the model, and Cristian Armendáriz-Picón at Syracuse University in New York agrees. He says the model Carlesi is using should undergo further tests that the cosmological constant has already passed. For example, its effects should be consistent with the integrated Sachs-Wolfe effect, in which photons from the cosmic microwave background experience slight changes in wavelength as they feel the gravity of superclusters of galaxies they pass through.

‘Tantalizing Hints’, No Direct Proof in Search for God Particle

December 13, 2011 Leave a comment

Peter Higgs

 [Reprint Warning: Original Article]

 

 Fabrice Coffrini/Keystone, via Associated Press

 

Physicists will have to keep holding their breath a little while longer.

Two teams of scientists sifting debris from high-energy proton collisions in the Large Hadron Collider at CERN, the European Center for Nuclear Research, said Tuesday that they had recorded “tantalizing hints” — but only hints — of a long-sought subatomic particle known as the Higgs boson, whose existence is a key to explaining why there is mass in the universe. It is likely to be another year, however, before they have enough data to say whether the elusive particle really exists, the scientists said.

The putative particle weighs in at about 125 billion electron volts, about 125 times heavier than a proton and 500,000 times heavier than an electron, according to one team of 3,000 physicists, known as Atlas, for the name of their particle detector. The other equally large team, known as C.M.S. — for their detector, the Compact Muon Solenoid — found bumps in their data corresponding to a mass of about 126 billion electron volts.

If the particle does exist at all, it must lie within the range of 115 to 127 billion electron volts, according to the combined measurements. “We cannot conclude anything at this stage,” said Fabiola Gianotti, the Atlas spokeswoman, adding, “Given the outstanding performance of the L.H.C. this year, we will not need to wait long for enough data and can look forward to resolving this puzzle in 2012.”

Over the last 20 years, suspicious bumps that might have been the Higgs have come and gone, and scientists cautioned that the same thing could happen again, but the fact that two rival teams using two different mammoth particle detectors had recorded similar results was considered to be good news. Physicists expect to have enough data to make the final call by the summer.

The Atlas result has a chance of less than one part in 5,000 of being due to a lucky background noise, which is impressive but far short of the standard for a “discovery,” which requires one in 3.5 million odds of being a random fluctuation. Showing off one striking bump in the data, Ms. Gianotti said, “If we are just being lucky, it will take a lot of data to kill it.”

Physicists around the world, fueled by coffee, dreams and Internet rumors of a breakthrough, gathered in lounges and auditoriums to watch a Webcast of a series of talks and a discussion of the results at CERN, the European Center for Nuclear Research, Tuesday morning. The results were posted on the Web.

As seen on the Webcast, the auditorium at CERN was filled to standing room only. At New York University, dozens of physicists gathered in a physics lounge burst into applause.

Categories: Astronomy, Cosmology, Science, Space

What Lies Beyond the Horizon of a Black Hole?

December 7, 2011 Leave a comment

 

[Reprint Alert: What Lies Beyond the Horizon of a Black Hole]

 

Do black holes hold the key that could unlock the secrets of our patch of the Universe? Some of the world’s leading physicists believe that in the event that quantum effects allow time to extend indefinitely into the past that it could be possible that beyond the event horizon of a black hole is the beginning of another universe.

Embedded in the heart of each of the Universe’s one trillion galaxies is a supermassive black hole that is roughly one million to one billion times the mass of the sun. About 10 percent of these giant black holes feature jets of plasma, or highly ionized gas, that extend in opposite directions of the black hole. By spewing huge amounts of mostly kinetic energy from the black holes into the Universe, the jets affect how stars and other bodies form, and play a crucial role in the evolution of clusters of galaxies, the largest structures in the Universe.

“This black hole in the center of the cluster is affecting everything else in that cluster,” said Dan Evans, a postdoctoral researcher at MIT’s Kavli Institute for Astrophysics and Space Research. Because a jet gently heats the gas it carries throughout a galaxy cluster, it can slow and even prevent stars, which are created by the condensation and collapse of cool molecular gas, from forming, thereby affecting the growth of galaxies, Evans explained. “Without these jets, clusters of galaxies would look very different.”

How these jets form remains one of the most important unsolved mysteries in extragalactic astrophysics. Now Evans may be one step closer to unlocking that mystery.

For two years, Evans has been comparing several dozen galaxies whose black holes host powerful jets (known as radio-loud active galactic nuclei, or AGN — like the image of the supermassive black hole at the center of the Milky Way shown above) to those galaxies with supermassive black holes that do not eject jets. All black holes — those with and without jets — feature accretion disks, the clumps of dust and gas rotating just outside their event horizon.

By examining the light reflected in the accretion disk of an AGN black hole, Evans has concluded that jets may form right outside black holes that have a retrograde spin — or which spin in the opposite direction from their accretion disk. Although Evans and a colleague recently hypothesized that the gravitational effects of black hole spin may have something to do with why some have jets.
 
While researchers know that the mass of a black hole is intimately linked to the galaxy in which it is located, they have, until now, known little about the role of its second fundamental property — spin. Evans asserts that spin is crucial to understanding the dynamics of a black hole’s host galaxy because it may actually create the jet that regulates the growth of that galaxy and the universe.

Although Evans has suspected for nearly five years that retrograde black holes with jets are missing the innermost portion of their accretion disk, it wasn’t until last year that computational advances meant that he could analyze data collected between late 2007 and early 2008 by the Suzaku observatory, a Japanese satellite launched in 2005 with collaboration from NASA, to provide an example to support the theory. With these data, Evans and colleagues from the Harvard-Smithsonian Center for Astrophysics, Yale University, Keele University and the University of Hertfordshire in the United Kingdom analyzed the spectra of a supermassive black hole with a jet located about 800 million light years away in an AGN named 3C 33.

Astrophysicists can see the signatures of X-ray emission from the inner regions of the accretion disk, which is located close to the edge of a black hole, as a result of a super hot atmospheric ring called a corona that lies above the disk and emits light that an observatory like Suzaku can detect. In addition to this direct light, a fraction of light passes down from the corona onto the black hole’s accretion disk and is reflected from the disk’s surface, resulting in a spectral signature pattern called the Compton reflection hump, also detected by Suzaku.

But Evans’ team never found a Compton reflection hump in the X-ray emission given off by 3C 33, a finding the researchers believe provides crucial evidence that the accretion disk for a black hole with a jet is truncated, meaning it doesn’t extend as close to the center of the black hole with a jet as it does for a black hole that does not have a jet. The absence of this innermost portion of the disk means that nothing can reflect the light from the corona, which explains why observers only see a direct spectrum of X-ray light.

The researchers believe the absence may result from retrograde spin, which pushes out the orbit of the innermost portion of accretion material as a result of general relativity, or the gravitational pull between masses. This absence creates a gap between the disk and the center of the black hole that leads to the piling of magnetic fields that provide the force to fuel a jet.

The field of research will expand considerably in August, 2011, with the planned launch of NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) satellite, which is 10 to 50 times more sensitive to spectra and the Compton reflection hump than current technology.

NuSTAR will help researchers conduct a “giant census” of supermassive black holes that “will absolutely revolutionize the way we look at X-ray spectra of AGN,” Evans explained. He plans to spend another two years comparing black holes with and without jets, hoping to learn more about the properties of AGN. His goal over the next decade is to determine how the spin of a supermassive black hole evolves over time.

A Brief Note on Consciousness

November 12, 2011 Leave a comment

God is the consciousness spawned by its own Creation. The Universe, including each and every instance of its parts; the stars; the galaxies; the beasts and the beauties – you and I – are the first and only instance of that Creative process.

This creation, once it began, has no choice but to continue onward and outward in all directions. You can personally witness this miracle by considering one of your own thoughts. A thought consists of the same basic substance of the essential “matter” of the universe itself. According to most current models of human physiology; a thought is comprised of an electrical impulse that travels along a neural pathway. At the same time, a thought consists of the physical matter that can be observed occurring as a C fiber activity in the brain. What is true of your thought is true of the universe as well. Modern physics tells us that in the world of the very small – the subatomic – at any moment, a quanta (the smallest discrete particle of existence) can be either “matter” or “energy”; it simply depends on the moment we choose to “observe” it.

Much like the universe and all “things” in it; there was a time in your brain when that thought did not exist. Then it was, and, still is. A thought occurs much like the ripples created by a stone tossed into a calm pond. What is different about our thoughts is that there is no shore! The thought simply continues on in all directions, on into infinity and beyond. Sometimes, there are related actions taken, more often the thought exists completely and only by itself.

What matters mostly, is that this thought and all other thoughts you or I or anyone has is made up of the same stuff as the fundamental building blocks of the entire universe. If you could look at any one of your thoughts as it occurred, you would witness a spectacular and startling show as magnificent as any star producing nebula albeit on a much smaller scale. And, when connected to the driving force of your intention, this thought has the creative force and sustaining quality of any creative force that has ever existed including the momentous force generated by the big bang itself!

As it turns out, there are five basic forces that comprise our universe, not four. Intention is that fifth force. Without intention the big bang is simply a great noise with spectacular momentary sights and sounds without permanent sustainability or continuing expanding substance. Intention functions exactly the same in our consciousness.

A thought might be just a thought; but a thought connected to our intention can move mountains!

[Abstracted from Science & Spiritualism by Robert Eugene Miller]

Happy Armageddon Day

October 22, 2011 Leave a comment

We Must Continue to Wonder

October 3, 2011 Leave a comment
Lisa Randall is Professor of Physics at Harvard University. She is one of today’s most influential and highly cited theoretical physicists, and has received numerous awards and honors for her contributions.

The following is excerpted from her book: Knocking on Heaven’s Door

WHAT’S SO SMALL TO YOU IS SO LARGE TO ME

Among the many reasons I chose to pursue physics was the desire to do something that would have a permanent impact. If I was going to invest so much time, energy, and commitment, I wanted it to be for something with a claim to longevity and truth. Like most people, I thought of scientific advances as ideas that stand the test of time.

My friend Anna Christina Büchmann studied English in college while I majored in physics. Ironically, she studied literature for the same reason that drew me to math and science. She loved the way an insightful story lasts for centuries. When discussing Henry Fielding’s novel Tom Jones with her many years later, I learned that the edition I had read and thoroughly enjoyed was the one she helped annotate when she was in graduate school.

Tom Jones was published 250 years ago, yet its themes and wit resonate to this day. During my first visit to Japan, I read the far older Tale of Genji and marveled at its characters’ immediacy too, despite the thousand years that have elapsed since Murasaki Shikibu wrote about them. Homer created the Odyssey roughly 2,000 years earlier. Yet notwithstanding its very different age and context, we continue to relish the tale of Odysseus’s journey and its timeless descriptions of human nature.

Scientists rarely read such old—let alone ancient—scientific texts. We usually leave that to historians and literary critics. We nonetheless apply the knowledge that has been acquired over time, whether from Newton in the seventeenth century or Copernicus more than 100 years earlier still. We might neglect the books themselves, but we are careful to preserve the important ideas they may contain.

Science certainly is not the static statement of universal laws we all hear about in elementary school. Nor is it a set of arbitrary rules. Science is an evolving body of knowledge. Many of the ideas we are currently investigating will prove to be wrong or incomplete. Scientific descriptions certainly change as we cross the boundaries that circumscribe what we know and venture into more remote territory where we can glimpse hints of the deeper truths beyond.

The paradox scientists have to contend with is that while aiming for permanence, we often investigate ideas that experimental data or better understanding will force us to modify or discard. The sound core of knowledge that has been tested and relied on is always surrounded by an amorphous boundary of uncertainties that are the domain of current research. The ideas and suggestions that excite us today will soon be forgotten if they are invalidated by more persuasive or comprehensive experimental work tomorrow.

When the 2008 Republican presidential candidate Mike Huckabee sided with religion over science—in part because scientific “beliefs” change whereas Christians take as their authority an eternal, unchanging God—he was not entirely misguided, at least in his characterization. The universe evolves and so does our scientific knowledge of it. Over time, scientists peel away layers of reality to expose what lies beneath the surface. We broaden and enrich our understanding as we probe increasingly remote scales. Knowledge advances and the unexplored region recedes when we reach these difficult-to-access distances. Scientific “beliefs” then evolve in accordance with our expanded knowledge.

Nonetheless, even when improved technology makes a broader range of observations possible, we don’t necessarily just abandon the theories that made successful predictions for the distances and energies, or speeds and densities, that were accessible in the past. Scientific theories grow and expand to absorb increased knowledge, while retaining the reliable parts of ideas that came before. Science thereby incorporates old established knowledge into the more comprehensive picture that emerges from a broader range of experimental and theoretical observations. Such changes don’t necessarily mean the old rules are wrong, but they can mean, for example, that those rules no longer apply on smaller scales where new components have been revealed. Knowledge can thereby embrace old ideas yet expand over time, even though very likely more will always remain to be explored. Just as travel can be compelling—even if you will never visit every place on the planet (never mind the cosmos)—increasing our understanding of matter and of the universe enriches our existence. The remaining unknowns serve to inspire further investigations.

My own research field of particle physics investigates increasingly smaller distances in order to study successively tinier components of matter. Current experimental and theoretical research attempt to expose what matter conceals—that which is embedded ever deeper inside. But despite the often-heard analogy, matter is not simply like a Russian matryoshka doll, with similar elements replicated at successively smaller scales. What makes investigating increasingly minuscule distances interesting is that the rules can change as we reach new domains. New forces and interactions might appear at those scales whose impact was too tiny to detect at the larger distances previously investigated.

The notion of scale, which tells physicists the range of sizes or energies that are relevant for any particular investigation, is critical to the understanding of scientific progress—as well as to many other aspects of the world around us. By partitioning the universe into different comprehensible sizes, we learn that the laws of physics that work best aren’t necessarily the same for all processes. We have to relate concepts that apply better on one scale to those more useful at another. Categorizing in this way lets us incorporate everything we know into a consistent picture while allowing for radical changes in descriptions at different lengths.

In this chapter, we’ll see how partitioning by scale—whichever scale is relevant—helps clarify our thinking—both scientific and otherwise— and why the subtle properties of the building blocks of matter are so hard to notice at the distances we encounter in our everyday lives. In doing so, this chapter also elaborates on the meaning of “right” and “wrong” in science, and why even apparently radical discoveries don’t necessarily force dramatic changes on the scales with which we are already familiar.

IT’S IMPOSSIBLE

People too often confuse evolving scientific knowledge with no knowledge at all and mistake a situation in which we are discovering new physical laws with a total absence of reliable rules. A conversation with the screenwriter Scott Derrickson during a recent visit to California helped me to crystallize the origin of some of these misunderstandings. At the time, Scott was working on a couple of movie scripts that proposed potential connections between science and phenomena that he suspected scientists would probably dismiss as supernatural. Eager to avoid major solecisms, Scott wanted to do scientific justice to his imaginative story ideas by having them scrutinized by a physicist—namely me. So we met for lunch at an outdoor café in order to share our thoughts along with the pleasures of a sunny Los Angeles afternoon.

Knowing that screenwriters often misrepresent science, Scott wanted his particular ghost and time-travel stories to be written with a reasonable amount of scientific credibility. The particular challenge that he as a screenwriter faced was his need to present his audience not just with interesting new phenomena, but also with ones that would translate effectively to a movie screen. Although not trained in science, Scott was quick and receptive to new ideas. So I explained to him why, despite the ingenuity and entertainment value of some of his story lines, the constraints of physics made them scientifically untenable.

Scott responded that scientists have often thought certain phenomena impossible that later turned out to be true. “Didn’t scientists formerly disbelieve what relativity now tells us?” “Who would have thought randomness played any role in fundamental physical laws?” Despite his great respect for science, Scott still wondered if—given its evolving nature—scientists aren’t sometimes wrong about the implications and limitations of their discoveries.

Some critics go even further, asserting that although scientists can predict a great deal, the reliability of those predictions is invariably suspect. Skeptics insist, notwithstanding scientific evidence, that there could always be a catch or a loophole. Perhaps people could come back from the dead or at the very least enter a portal into the Middle Ages or into Middle-earth. These doubters simply don’t trust the claims of science that a thing is definitively impossible.

However, despite the wisdom of keeping an open mind and recognizing that new discoveries await, a deep fallacy is buried in this logic. The problem becomes clear when we dissect the meaning of such statements as those above and, in particular, apply the notion of scale. These questions ignore the fact that although there will always exist unexplored distance or energy ranges where the laws of physics might change, we know the laws of physics on human scales extremely well. We have had ample opportunity to test these laws over the centuries.

When I met the choreographer Elizabeth Streb at the Whitney Museum, where we both spoke on a panel on the topic of creativity, she too underestimated the robustness of scientific knowledge on human scales. Elizabeth posed a similar question to those Scott had asked: “Could the tiny dimensions proposed by physicists and curled up to an unimaginably small size nonetheless affect the motion of our bodies?”

Her work is wonderful, and her inquiries into the basic assumptions about dance and movement are fascinating. But the reason we cannot determine whether new dimensions exist, or what their role would be even if they did, is that they are too small or too warped for us to be able to detect. By that I mean that we haven’t yet identified their influence on any quantity that we have so far observed, even with extremely detailed measurements. Only if the consequences of extra dimensions for physical phenomena were vastly bigger could they discernibly influence anyone’s motion. And if they did have such a significant impact, we would already have observed their effects. We therefore know that the fundamentals of choreography won’t change even when our understanding of quantum gravity improves. Its effects are far too suppressed relative to anything perceptible on a human scale.

When scientists have turned out to be wrong in the past, it was often because they hadn’t yet explored very tiny or very large distances or extremely high energies or speeds. That didn’t mean that, like Luddites, they had closed their minds to the possibility of progress. It meant only that they trusted their most up-to-date mathematical descriptions of the world and their successful predictions of then-observable objects and behaviors. Phenomena they thought were impossible could and sometimes did occur at distances or speeds these scientists had never before experienced—or tested. But of course they couldn’t yet have known about new ideas and theories that would ultimately prevail in the regimes of those tiny distances or enormous energies with which they were not yet familiar.

When scientists say we know something, we mean only that we have certain ideas and theories whose predictions have been well tested over a certain range of distances or energies. These ideas and theories are not necessarily the eternal laws for the ages or the most fundamental of physical laws. They are rules that apply as well as any experiment could possibly test, over the range of parameters available to current technology. This doesn’t mean that these laws will never be overtaken by new ones. Newton’s laws are instrumental and correct, but they cease to apply at or near the speed of light where Einstein’s theory applies. Newton’s laws are at the same time both correct and incomplete. They apply over a limited domain.

The more advanced knowledge that we gain through better measurements really is an improvement that illuminates new and different underlying concepts. We now know about many phenomena that the ancients could not have derived or discovered with their more limited observational techniques. So Scott was right that sometimes scientists have been wrong—thinking phenomena impossible that in the end turned out to be perfectly true. But this doesn’t mean there are no rules. Ghosts and time-travelers won’t appear in our houses, and alien creatures won’t suddenly emerge from our walls. Extra dimensions of space might exist, but they would have to be tiny or warped or otherwise currently hidden from view in order for us to explain why they have not yet yielded any noticeable evidence of their existence.

Exotic phenomena might indeed occur. But such phenomena will happen only at difficult-to-observe scales that are increasingly far from our intuitive understanding and our usual perceptions. If they will always remain inaccessible, they are not so interesting to scientists. And they are less interesting to fiction writers too if they won’t have any observable impact.

Weird things are possible, but the ones non-physicists are understandably most interested in are the ones we can observe. As Steven Spielberg pointed out in a discussion about a science fiction movie he was considering, a strange world that can’t be presented on a movie screen—and which the characters in a film would never experience—is not so interesting to a viewer. Only a new world that we can access and be aware of could be. Even though both require imagination, abstract ideas and fiction are different and have different goals. Scientific ideas might apply to regimes that are too remote to be of interest to a film, or to our daily observations, but they are nonetheless essential to our description of the physical world.