Videos by topic: UNIVERSE
Computation All the Way Down
We're now in this situation where people just assume that science can compute everything, that if we have all the right input data and we have the right models, science will figure it out. If we learn that our universe is fundamentally computational, that throws us right into the idea that computation is a paradigm you have to care about. The big transition was from using equations to describe how everything works to using programs and computation to describe how things work. And that's a transition that's happened after 300 years of equations. The transition time to using programs has been remarkably quick, a decade or two. One area that was a holdout, despite the transition of many fields of science into the computational models direction, was fundamental physics.
If we can firmly establish this fundamental theory of physics, we know it's computation all the way down. Once we know it's computation all the way down, we're forced to think about it computationally. One of the consequences of thinking about things computationally is this phenomenon of computational irreducibility. You can't get around it. That means we have always had the point of view that science will eventually figure out everything, but computational irreducibility says that can't work. It says even if we know the rules for system, it may be the case that we can't work out what that system will do any more efficiently than basically just running the system and seeing what happens, just doing the experiment so to speak. We can't have a predictive theoretical science of what's going to happen.
STEPHEN WOLFRAM is a scientist, inventor, and the founder and CEO of Wolfram Research. He is the creator of the symbolic computation program Mathematica and its programming language, Wolfram Language, as well as the knowledge engine Wolfram|Alpha. He is also the author, most recently, of A Project to Find the Fundamental Theory of Physics. Stephen Wolfram's Edge Bio Page
The Causal Theory of Views
An event has a view of the world. First, let me tell you what I mean by a view. A view is the information about how it fits into the rest of the world that that event has. That includes who its parents are and what the energy and momentum was that was propagated to it. My view of the world is, I look out and light comes up from the past and I see a pattern of colors, which come from photons of different energies striking my eye. That's my view; it's a property of a moment. That contains all that I, as an event, know about how I fit into the rest of the world.
Now, if you know the things that I just said were real—the events, the causal relations, the distribution of energy and momentum flowing—I can tell you what the view of each event is, but I can also flip it around. There's a dual description in which I just say what the views are and that's the whole description. So, I just say there's a view, and that view is and hears a kind of picture. You see the sky, a two-dimensional sphere around you, and there are some colors, which are photons coming in of different energies—that's the view. I can hypothesize that all that exists in the world is views and a process that continually makes new views out of old views. That's what I call the causal theory of views.
LEE SMOLIN is a theoretical physicist who has been, since 2001, a founding and senior faculty member at Perimeter Institute for Theoretical Physics. His main contributions have been so far to the quantum theory of gravity, to which he has been a co-inventor and major contributor to two major directions, loop quantum gravity and deformed special relativity. He is the author, most recently, of Einstein's Unfinished Revolution. Lee Smolin's Edge Bio Page
The Universe Is Not in a Box
One of the great books in science was published in 1824 by a young Frenchman called Sadi Carnot. This is one of the most wonderful books, the title of which is Reflections on the Motive Power of Fire. In about six pages, he explains how you would make a steam engine that would work with the absolute maximum efficiency possible. It was almost entirely ignored, and he died before anything much could come out of it. It was rediscovered in 1849 when William Thomson, who later became Lord Kelvin, wrote a paper which publicized this work. Within a couple of years, thermodynamics had been created as a science.
It caused a tremendous lot of excitement from the 1850s onwards. The key thing about this work of Carnot's is that if you have a steam engine, the steam has to remain in a cylinder in a box. You want the steam engine to work continuously, so you keep on having to bring the steam and the cylinder back to the condition it was before. It's remarkable that the development of what's called statistical mechanics—understanding how steam behaves—led to the discovery of entropy, one of the great discoveries in the history of science, and it was all followed out of this work of Carnot on how steam engines work. And moreover, it was very anthropocentric thinking about how human beings could exploit coal to drive steam engines and do work for them. At that stage, nobody was thinking about the universe as a whole; they were just thinking about how they could make steam engines work better.
This way of thinking, I believe, has survived more or less unchanged to this day. You still find that people who work on this problem of the arrow of time are still assuming conditions that are appropriate for a steam engine. But in the 1920s and early 1930s, Hubble showed that the universe was expanding, that we live in an expanding universe. Is that going to be well modeled by steam in a box? My belief is that people haven't realized that we have to think out of the box. We have to think in different ways. We keep on finding ways in which the mathematics that was developed before to understand systems confined in a box have to be modified with quite surprising consequences and, above all, possibly to explain why we have this incredibly powerful sense of the passage of time, why the past is so different from the future.
JULIAN BARBOUR is a theoretical physicist specializing in the study of time and motion; visiting professor of physics at the University of Oxford; and author of The Janus Point (forthcoming) and The End of Time. Julian Barbour's Edge Bio Page
Looking in the Wrong Places
We should be very careful in thinking about whether we’re working on the right problems. If we don’t, that ties into the problem that we don’t have experimental evidence that could move us forward. We're trying to develop theories that we use to find out which are good experiments to make, and these are the experiments that we build.
We build particle detectors and try to find dark matter; we build larger colliders in the hope of producing new particles; we shoot satellites into orbit and try to look back into the early universe, and we do that because we hope there’s something new to find there. We think there is because we have some idea from the theories that we’ve been working on that this would be something good to probe.
If we are working with the wrong theories, we are making the wrong extrapolations, we have the wrong expectations, we make the wrong experiments, and then we don’t get any new data. We have no guidance to develop these theories. So, it’s a chicken and egg problem. We have to break the cycle. I don’t have a miracle cure to these problems. These are hard problems. It’s not clear what a good theory is to develop. I’m not any wiser than all the other 20,000 people in the field.
SABINE HOSSENFELDER is a research fellow at the Frankfurt Institute for Advanced Studies, an independent, multidisciplinary think tank dedicated to theoretical physics and adjacent fields. She is also a singer-songwriter whose music videos appear on her website sabinehossenfelder.com (see video below). Sabine Hossenfelder's Edge Bio Page
Shut Up and Measure
What is fascinating to me is that we are now hoping, with modern measurements, to probe the early Universe. In doing so, we’re encountering deep questions about the scientific method and questions about what is fundamental to physics. When we look out on the Universe, we’re looking through this dirty window, literally a dusty window. We look out through dust in our galaxy. And what is that dust? I like to call it nano planets, tiny grains of iron and carbon and silicon—all these things that are the matter of our solar system. They’re the very matter that Galileo was looking through when he first glimpsed the Pleiades and the stars beyond the solar system for the first time.
When we look out our telescopes, we never see just what we're looking for. We have to contend with everything in the foreground. And thank goodness for that dust in the foreground, for without it, we would not be here.
BRIAN KEATING is a professor of physics at the Center for Astrophysics & Space Sciences at the University of California, San Diego. Brian Keating's Edge Bio page
Curtains For Us All?
Here on Earth, I suspect that we are going to want to regulate the application of genetic modification and cyborg techniques on grounds of ethics and prudence. This links with another topic I want to come to later, which is the risks of new technology. If we imagine these people living as pioneers on Mars, they are out of range of any terrestrial regulation. Moreover, they've got a far higher incentive to modify themselves or their descendants to adapt to this very alien and hostile environment.
They will use all the techniques of genetic modification, cyborg techniques, maybe even linking or downloading themselves into machines, which, fifty years from now, will be far more powerful than they are today. The post-human era is probably not going to start here on Earth; it will be spearheaded by these communities on Mars. That's the vision I would have of Mars. It's people out there who will perhaps lead to these developments, which will then eventually lead to posthumans, maybe electronic rather than organic, spreading far beyond our solar system. If that's happened elsewhere, that's the sort of thing we might detect.
LORD MARTIN REES is a Fellow of Trinity College and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge. He is the UK's Astronomer Royal and a Past President of the Royal Society. Martin Rees's Edge Bio Page
Quantum Hanky-Panky
Thinking about the future of quantum computing, I have no idea if we're going to have a quantum computer in every smart phone, or if we're going to have quantum apps or quapps, that would allow us to communicate securely and find funky stuff using our quantum computers; that's a tall order. It's very likely that we're going to have quantum microprocessors in our computers and smart phones that are performing specific tasks.
This is simply for the reason that this is where the actual technology inside our devices is heading anyway. If there are advantages to be had from quantum mechanics, then we'll take advantage of them, just in the same way that energy is moving around in a quantum mechanical kind of way in photosynthesis. If there are advantages to be had from some quantum hanky-panky, then quantum hanky‑panky it is.
SETH LLOYD, Professor, Quantum Mechanical Engineering, MIT; Principal Investigator, Research Laboratory of Electronics; Author, Programming the Universe. Seth Lloyd's Edge Bio Page
Sounds of the Skies
The effect of these gravitational waves is to squeeze and stretch space. If you were floating near these black holes, you would literally be squeezed and stretched. If you were close enough, you would feel the difference between the squeezing and stretching on your face or your feet. We’ve even conjectured that your eardrum could ring in response, like a resonant membrane, so that you would literally hear the wave, hear it even in the absence of a medium like air. Even though we think that empty space is silent, in these circumstances you would hear the black holes collide but you wouldn’t see them; it would happen in complete darkness. The two black holes would be completely dark, and your only evidence of their collision would be to hear the spacetime ringing.
JANNA LEVIN is a professor of physics and astronomy at Barnard College of Columbia University. She is the author of How the Universe Got Its Spots; A Madman Dreams of Turing Machines; and most recently, Black Hole Blues and Other Songs from Outer Space. Janna Levin's Edge Bio Page
The Exquisite Role of Dark Matter
It is definitely the golden age in cosmology because of this unique confluence of ideas and instruments. We live in a very peculiar universe—one that is dominated by dark matter and dark energy—the true nature of both of these remains elusive. Dark matter does not emit radiation in any wavelength and its presence is inferred by its gravitational influence on the motions of stars and gas in its vicinity. Dark Energy, discovered in 1998, meanwhile is believed to be powering the accelerated expansion of the universe. Despite not knowing what the dark matter particle is or what dark energy really is, we still have a very successful theory of how galaxies form and evolve in a universe with these mysterious and invisible dominant components. Technology has made possible the testing of our cosmological theories at a level that was unprecedented before. All of these experiments have delivered very exciting results, even if they're null results. For example, the LHC, with the discovery of the Higgs, has given us a lot more comfort in the standard model. The Planck and WMAP satellites probing the leftover hiss from the Big Bang—the cosmic microwave background radiation—have shown us that our theoretical understanding of how the early fluctuations in the universe grew and formed the late universe that we see is pretty secure. Our current theory, despite the embarrassing gap of not knowing the true nature of dark matter or dark energy, has been tested to a pretty high degree of precision.
It's also consequential that the dark matter direct detection experiments have not found anything. That's interesting too, because that's telling us that all these experiments are reaching the limits of their sensitivity, what they were planned for, and they're still not finding anything. This suggests paradoxically that while the overall theory might be consistent with observational data, something is still fundamentally off and possibly awry in our understanding. The challenge in the next decade is to figure out which old pieces don't fit. Is there a pattern that emerges that would tell us, is it a fundamentally new theory of gravity that's needed, or is it a complete rethink of some aspects of particle physics that are needed? Those are the big open questions.
PRIYAMVADA NATARAJAN is a professor in the Departments of Astronomy and Physics at Yale University, whose research is focused on exotica in the universe—dark matter, dark energy, and black holes. Priyamvada Natarajan's Edge Bio Page
Layers Of Reality
We know there's a law of nature, the second law of thermodynamics, that says that disorderliness grows with time. Is there another law of nature that governs the complexity of what happens? That talks about multiple layers of the structures and how they interact with each other? Embarrassingly enough, we don't even know how to define this problem yet. We don't know the right quantitative description for complexity. This is very early days. This is Copernicus, not even Kepler, much less Galileo or Newton. This is guessing at the ways to think about these problems.
SEAN CARROLL is a research professor at Caltech and the author of The Particle at the End of the Universe, which won the 2013 Royal Society Winton Prize, and From Eternity to Here: The Quest for the Ultimate Theory of Time. He has recently been awarded a Guggenheim Fellowship, the Gemant Award from the American Institute of Physics, and the Emperor Has No Clothes Award from the Freedom From Religion Foundation. Sean Carroll's Edge Bio Page