This Is Why Scientists Will Never Exactly Solve General Relativity
“One of the most valuable lessons I ever got in my life came during the first day of my first college math class on differential equations. The professor told us, “Most of the differential equations that exist cannot be solved. And most of the differential equations that can be solved cannot be solved by you.” This is exactly what General Relativity is — a series of coupled differential equations — and the difficulty that it presents to all those who study it.
We cannot even write down the Einstein field equations that describe most spacetimes or most Universes we can imagine. Most of the ones we can write down cannot be solved. And most of the ones that can be solved cannot be solved by me, you, or anyone. But still, we can make approximations that allow us to extract some meaningful predictions and descriptions. In the grand scheme of the cosmos, that’s as close as anyone’s ever gotten to figuring it all out, but there’s still much farther to go. May we never give up until we get there.”
In our best theory of gravity, General Relativity, we can compute to arbitrary accuracy the effects on matter of any spacetime that we can write down. Unfortunately, most of the spacetimes that we can dream up in our head aren’t ones that we can write down, and most of the ones that we can write down can only be solved approximately, not exactly.
This is not a flaw nor a benefit: it is simply a property of the theory that we have. Is it the final answer? Perhaps not. But it’s the best one we’ve got so far. Here’s what it means.
Your 2019 Holiday Gift Guide For Space, Astronomy, And Science Lovers
“At The Edge Of Time, by Dan Hooper. This new book, out just a few weeks ago, is my favorite new science book of 2019. As a theoretical cosmologist, Dan is all the things I appreciate in a scientist who writes about his own research: he’s knowledgeable, comprehensive, and careful to get the details right. He has clear opinions and preferences, but is willing and able to push them aside in service of teaching the reader about the strengths and weaknesses of a variety of perspectives on a myriad of issues at the frontiers of physics.
If you’re mystified and curious about the mysteries of the Universe, including dark matter, dark energy, and cosmic inflation, and want a unique take on all of these puzzles with a peek behind how science-in-action works, you won’t want to miss this book. (I liked it so much that Dan is going to be my next upcoming guest on the Starts With A Bang podcast!)”
Do you love space, science, astronomy, physics, the Moon, and learning about the frontiers of what we know? Well, the holidays are coming up (today is Black Friday), and if that describes you or someone close to you in your life, here is a complete gift guide for the science enthusiast in your life.
With a total of 11 recommended books, a wall calendar, hats, accessories, and even a unique puzzle, you won’t want to miss this holiday gift guide!
This Is Why ‘Multi-Messenger Astronomy’ Is The Future Of Astrophysics
“The three types of signals we know how to collect from the Universe — light, particles, and gravitational waves — all deliver fundamentally different types of information right to our front door. By combining the most precise observations we can take with each of these, we can learn more about our cosmic history than any one of these signal types, or “messengers,” can provide in isolation.
We’ve already learned how neutrinos are produced in supernova, and how their travel path is less impeded by matter than light’s is. We’ve already linked merging neutron stars with kilonovae and the production of the heaviest elements in the Universe. With multi-messenger astronomy still in its infancy, we can expect a deluge of new events and new discoveries as this science progresses throughout the 21st century.
Just as you can learn more about a tiger by hearing its growl, smelling its scent, and watching it hunt than you can from a still image alone, you can learn more about the Universe by detecting these fundamentally different types of messengers all at once. Our bodies might be limited in terms of the senses we can use in any given scenario, but our knowledge of the Universe is limited only by the fundamental physics governing it. In the quest to learn it all, we owe it to humanity to use every resource we can muster.”
In 2017, three different gravitational wave observatories from across the world, LIGO Livingston, LIGO Hanford, and the Virgo detector all witnessed the arrival of gravitational waves from a neutron star collision some 130,000,000 light-years away. Two seconds after the wave signal ceased, the first light from the merger arrived. A new term that was previously reserved for professional astronomers, “multi-messenger astronomy,” suddenly entered the public arena.
But what is multi-messenger astronomy? What makes something a “messenger” and why is it important? As it turns out, it’s going to revolutionize how we understand our Universe in the 21st century. Come find out how today.
6 Steps Everyone Can Take To Become An Ally In White, Male-Dominated Workplaces
“Step 1: Listen to (women/people of color/URMs) when they discuss the problems they face. This is the first real step towards being an ally, and all it requires you do to is pay attention to the many voices out there — especially the voices of people whose experiences are vastly different from your own — and pay attention to them.
You’ll find lots of challenges that they talk about, and a myriad of ways that people are given the message that they are inadequate. This is a problem that practically everyone faces, but the degree of severity of this problem varies drastically among people of different races, genders, sexual orientations, religions, and ages. Many things that we think of as minor offenses if they only happen once or twice become unbearable, like death-by-a-thousand-papercuts, when they happen continually.”
So, you’ve chosen the field you want to go into, and it’s a field where your talents and interest both lie. You know you’re good enough to do it, but you know there are going to be formidable obstacles and challenges to overcome. If that field happens to be dominated by white men (the dominant culture in many STEM fields), and you yourself aren’t a white man, you’re no doubt going to encounter obstacles and challenges that go above and beyond what you’d face if you were a white man.
You have a choice as far as how you behave in this environment, particularly if you yourself are a white man. If you’re interested in being an ally, you might find this essential reading.
What Came First: Inflation Or The Big Bang?
“In fact, our entire observable Universe contains no signatures at all from almost all of its pre-hot-Big-Bang history; only the final 10^-32 seconds (or so) of inflation even leave observably imprinted signatures on our Universe. We do not know where the inflationary state came from, however. It might arise from a pre-existing state that does have a singularity, it might have existed in its inflationary form forever, or the Universe itself might even be cyclical in nature.
There are a lot of people who mean “the initial singularity” when they say “the Big Bang,” and to those people, I say it’s long past due for you to get with the times. The hot Big Bang cannot be extrapolated back to a singularity, but only to the end of an inflationary state that preceded it. We cannot state with any confidence, because there are no signatures of it even in principle, what preceded the very end-stages of inflation. Was there a singularity? Maybe, but even if so, it doesn’t have anything to do with the Big Bang.”
Have you heard that our Universe began some 13.8 billion years ago with the start of the Big Bang? There’s a good chance that some version of that story has made it to you, but it unfortunately has probably gotten to you the same way it got to me: with an error that’s many decades out of date.
What if I told you that you couldn’t extrapolate the Universe back to a singularity, where all the matter and energy was consolidated into a space so tiny that the laws of physics break down?
What if I told you that we have a verified, validated theory of what happened before the Big Bang, and it has (for decades, now) superseded and replaced the idea of an initial singularity as the earliest stages of the Universe?
Meet cosmic inflation, the pre-origin of our Universe that set up and gave rise to the Big Bang, and learn why the naysayers are out of legs to stand on.
The 3 Most Important Questions Every Prospective Grad Student Must Face
“1.) Does this department have the overall strength to give me the educational foundation I need? In practically every graduate program, there are a series of core courses that every student takes, a series of elective courses that you’ll begin to take as you become more specialized, and research you must perform as part of your degree program.
The courses you take will lay the foundation for your future research, and the formal and informal conversations and inquiries you have and conduct with everyone in your department — peers, postdoctoral researchers and professors — will be instrumental in giving you the breadth and depth you need to succeed in your future endeavors. That’s why it’s vital to choose a program whose overall strength and intellectual diversity are well-suited to your educational goals.”
It’s that time of year again: where college seniors and the already-graduated begin applying to graduate schools to further their education. While every individual case is different, there are some useful questions that cut across fields, demographics, and even across vastly different personalities.
If you’re considering going to graduate school, there are a number of challenges you’re going to face, but many of them are foreseeable. If you’re interested in learning from the collective experiences of others who’ve gone through the rigamarole, you’re in luck: there’s some really good advice just waiting for you.
If you can formulate and think about these three particular questions, you’ll put yourself in the best shape possible going into graduate school. Make sure to share with those who need to see it!
This Is Why ‘Physical Cosmology’ Was Long Overdue For The 2019 Nobel Prize
“It is a spectacular fact of modern science that the predictions of theoretical cosmology have been verified and validated by ever-improving observations and measurements. Even more remarkably, when we examine the full suite of the cosmic data humanity has ever collected, one single picture accurately describes every observation together: a 13.8 billion year old Universe that began with the end of cosmic inflation, resulting in a Big Bang, where the Universe is comprised of 68% dark energy, 27% dark matter, 4.9% normal matter, 0.1% neutrinos, and a tiny bit of radiation with no spatial curvature at all.
Put those ingredients into your theoretical Universe with the right laws of physics and enough computational power, and you’ll obtain the vast, rich, expanding and evolving Universe we have today. What was initially an endeavor of just a handful of people has now become the modern precision science of cosmology. In the middle of the 20th century, legendary physics curmudgeon Lev Landau famously said, “Cosmologists are often in error but seldom in doubt.” With the 2019 Nobel Prize in Physics going to Jim Peebles, perhaps the world will recognize it’s long past time to retire Landau’s quote. We may live in a dark Universe, but the science of physical cosmology has shed a light on it like nothing else.”
I see you out there. You, the person who’s skeptical of dark matter. You, the one who thinks dark energy must be an enormous cosmological mistake. You, who thinks the Big Bang is a hoax and that inflation is a band-aid for a failing theory. And you, especially you, the one who derides cosmology as a pseudoscience, quoting Landau like his more-than-60-year-old quote is still relevant.
Physical cosmology is a real, robust science. It’s not only my field, but my grand-advisor, Jim Peebles, won the 2019 Nobel Prize for his work pioneering it. Come learn what all the fuss is really about.
Did Our Universe’s Structure Grow From The Top-Down Or From The Bottom-Up?
“A century ago, we didn’t even know what our Universe looked like. We didn’t know where it came from, whether or when it began, how old it was, what it was made out of, whether it was expanding, what was present within it. Today, we have scientific answers to all of these questions to within about 1% accuracy, plus a whole lot more.
The Universe was born almost perfectly uniform, with 1-part-in-30,000 imperfections present on practically all scales. The largest cosmic scales have slightly larger imperfections than the smaller ones, but the smaller ones are also substantial and collapse first. We likely formed the first stars just 50-to-200 million years after the Big Bang; the first galaxies arose 200-to-550 million years after the Big Bang; the largest galaxy clusters took billions of years to get there.
The Universe is neither top-down nor bottom-up, but a combination of both that implies it was born with an almost scale-invariant spectrum. With future survey telescopes such as LSST, WFIRST, and the next-generation of 30-meter-class ground-based telescopes, we’re poised to measure galaxy clustering as never before. After a lifetime of uncertainty, we can finally give a scientific answer to understanding how our Universe’s large-scale structure came to be.”
In a top-down scenario, the Universe would form structures on large scales first, then fragment to form individual galaxies. In a bottom-up scenario, the Universe forms tiny structures first, which then collect and clump under their own gravity to bring about a Universe rich in large-scale structure. So, which one is the Universe we have?
As is often the case, the answer is much more complex than just one of these two possibilities. Come get the full story today.
Advances Vs. Consequences: What Does The 21st Century Have In Store For Humanity?
“We now live in a time where the actions of a small group of people — whether through malicious or benign intentions — are capable of leading to global catastrophe. It’s not just climate change or the threat of nuclear war that hangs over us; it’s a slew of facts.
It matters that a mass extinction is occurring right now: we’re destroying this planet’s proverbial “book of life” before we’ve even read it.
It matters that computers are permeating ever-increasing facets of our life, as humanity’s recently rising electricity use (after a plateau earlier this decade) is almost entirely due to new computational uses, like cryptocurrencies and blockchain.
It matters that the population is greater than ever before, as managing and distributing the edible food and drinkable water we produce is a greater challenge than ever before.”
Do you like big, sweeping conversations that tackle the biggest existential questions facing our species today? Looking to the larger picture, of humanity’s future on Earth, scientist Martin Rees has written a book detailing the challenges facing our civilization in the 21st century, and is about to deliver a public lecture on the topic of navigating the course that could lead us into a true golden age… or to ruin.
I’ll be live-blogging the lecture with many thoughts to add, and I hope you’ll join me in enjoying it!
Was Dark Matter Really Created Before The Big Bang?
“So if that’s what the observational data points towards, what can we say about where dark matter comes from? A recent headline that made quite a splash claimed that dark matter may have originated before the Big Bang, and many people were confused by this assertion.
It might seem counterintuitive, because the way most people conceive of the Big Bang is as a singular point of infinite density. If you say the Universe is expanding and cooling today, then you can extrapolate it back to a state where all the matter and energy was compressed into a single point in space: a singularity. This corresponds to an initial start time for our Universe — the beginning of our Universe — and that’s the Big Bang.
So how could something that exists in our Universe, like dark matter, have originated before the Big Bang? Because the Big Bang wasn’t actually the beginning of space and time.”
Last month, a paper came out claiming that dark matter may have been created before the Big Bang. Although it might sound implausible, it’s absolutely a possibility that we cannot rule out, although it might be an idea that’s extraordinarily difficult to test when we compare it up against the other options. We have to keep every scenario that hasn’t been ruled out in mind, and understand that despite all we don’t know about dark matter, there’s a ton of indirect evidence brought to us by the full suite of observations at our disposal.
Could dark matter have been created before the Big Bang? Yes, but three other possibilities are maybe even more viable. Come find out why today.