Ask Ethan: If Mass Curves Spacetime, How Does It Un-Curve Again?
“We are taught that mass warps spacetime, and the curvature of spacetime around mass explains gravity – so that an object in orbit around Earth, for example, is actually going in a straight line through curved spacetime. Ok, that makes sense, but when mass (like the Earth) moves through spacetime and bends it, why does spacetime not stay bent? What mechanism un-warps that area of spacetime as the mass moves on?”
You’ve very likely heard that according to Einstein, matter tells spacetime how to curve, and that curved spacetime tells matter how to move. This is true, but then why doesn’t spacetime remain curved when a mass that was once there is no longer present? Does something cause space to snap back to its prior, un-bent position? As it turns out, we need to think pretty hard about General Relativity to get this right in the first place at all. It isn’t just the locations and magnitudes of masses that determine how objects move through space, but a series of subtle effects that must all be added together to get it right. When we do, we find out that uncurving this space actually results in gravitational radiation: ripples in space that have been observed and confirmed.
The deciding results are actually decades old, and were indirect evidence for gravitational waves long before LIGO. Come get the answer today!
This Is Why Physicists Think String Theory Might Be Our ‘Theory Of Everything’
“String theory offers a path to quantum gravity, which few alternatives can truly match. If we make the judicious choices of “the math works out this way,” we can get both General Relativity and the Standard Model out of it. It’s the only idea, to date, that gives us this, and that’s why it’s so hotly pursued. No matter whether you tout string theory’s successes or failure, or how you feel about its lack of verifiable predictions, it will no doubt remain one of the most active areas of theoretical physics research. At its core, string theory stands out as the leading idea of a great many physicists’ dreams of an ultimate theory.”
You don’t have to be a fan of string theory to understand why it’s such a promising area of scientific research. One of the holy grails of physics is for a quantum theory of gravitation: that describes gravity on the same footing as the other three forces, in very strong fields and at very tiny distances. Surprisingly, by looking at analogies between gravity and field theories, replacing particles with strings might be the answer.
It’s an incredibly difficult concept to understand why this would be the case without a slew of advanced mathematics, but in 2015, the world’s leading string theorist, Ed Witten, tried. That is to say, he wrote a piece for other physicists entitled, “What every physicist should know about string theory.”
But what if you want to understand it and you’re not a physicist? Then you should read this.
The 5 Most Important Rules For Scientists Who Write About Science
“Remember that your number one goal, if you’re a scientist writing about your science, is to increase the excitement and knowledge of your audience about what it is that you do. What we’re learning about all aspects of the Universe is expanding and increasing every day, and that joy and wonder should carry over to all of us in our daily lives. We cannot be experts in each and every field, but that underscores exactly why we need experts, and to respect true expertise when we encounter it.
If we take care to communicate responsibly, we can all gain a greater awareness of what it is that we do understand, as well as an appreciation for what that knowledge means. We may never run out of questions to ponder about the Universe itself, but with a little care and effort, we can all come a little bit closer to comprehending the answers.”
For most of us, we recognize that our expertise is extremely limited in all but a few areas. In order to learn what’s going on at the cutting edge of human knowledge, we have to go to the experts. In fields like physics, astronomy, biology, and chemistry, that means going to the scientists who study those fields. Yet scientists who communicate their own science often are some of the worst communicators out there, either getting mired in the details and losing the big picture or oversimplifying things to the point where they misinform their audience. Yet, if they just followed these five rules, they could avoid the most common mistakes and do what they set out to: inform the world about what they do and why it matters.
Come get the five most important rules for scientists who write about science. I bet you find value here even if you’re not a scientist yourself!
This Is Why The Event Horizon Telescope Still Doesn’t Have An Image Of A Black Hole
“Of all the black holes visible from Earth, the largest is at the galactic center: 37 μas.
With a theoretical resolution of 15 μas, the EHT should resolve it.
Despite the incredible news that they’ve detected the black hole’s structure at the galactic center, however, there’s still no direct image.”
Last year, data from the South Pole Telescope, a 10-meter radio telescope located at the South Pole, was added to the Event Horizon Telescope team’s overall set of information. Here we are, though, half a year later, and we still don’t have a direct image of the event horizon for the galactic center’s black hole. There aren’t any problems; the issue is that we have to successfully calibrate and error-correct the data, and that takes time and care to get it right. Science isn’t about getting the answer in the time you have to get it; it’s about getting the right answer in the time it takes to get things right. From that point of view, there’s every reason this is worth waiting for.
The Event Horizon Telescope team is on the right track; here’s where we are right now in our quest to create the first image of a black hole’s event horizon!
Did Han Solo Use A Trick Of Einstein’s Relativity To Make The Kessel Run?
“To move quickly between two points in space, then, even a straight line might be a disastrous plan. If what you need to do is avoid a large number of potentially hazardous objects, going around might be the only option. This could mean adding a very large distance to your expected path length, perhaps adding many light years to your journey. A straight-line path might be much shorter, but much more dangerous. But the shortest path of all won’t be a straight line, but an intricately curved path through the densest, most dangerous environment of all: a field of stars, planets, black holes, gas, dust, and more. To make the Kessel Run, the Millennium Falcon may have had to go through the center of that legendary galaxy far, far away.”
Was the Kessel Run a legend concocted by Han Solo to try and trick Luke and Obi-Wan? Or was it really a long run, that somehow the Millennium Falcon made in a shorter distance than was ever thought possible? That last possibility is intriguing, because physics allows it to be so. You normally think that the shortest distance between two points is a straight line, but this isn’t so in General Relativity. In truth, a curved path may be shorter, owing to the simple fact that masses are present, and they curve the fabric of spacetime. It’s possible that understanding _the force_ in Star Wars may not be as important, even for a pilot, as understanding the gravitational force in a galaxy far, far away.
Come see how a trick of Einstein’s Relativity might have made the Kessel Run possible!
The Most Important Equation In The Universe
“The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it’s headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!”
In 1915, Einstein put forth General Relativity as a new theory of gravity. It reproduced all of Newton’s earlier successes, solved the problem that Newton couldn’t of Mercury’s orbit, and made a new prediction of bent starlight by large masses, verified during the 1919 solar eclipse. Despite the fact that it included a cosmological constant to keep the Universe static, that didn’t deter Soviet physicist Alexander Friedmann from solving Einstein’s equations for a Universe that was filled with matter and energy, all the way back in 1922. The two generic equations he found, known as the Friedmann equations, immediately related measurable quantities like the amount of matter in the Universe to the expansion or contraction rate, which just years later became validated by Hubble’s observations. But the young Friedmann never lived to see it; he died of typhoid fever contracted when he was returning from his honeymoon in 1925.
Nearly 100 years later, it still stands as the equation that determines the history and fate of the Universe. Come see why I call it the most important equation in the Universe!
Einstein’s Ultimate Test: Star S0-2 To Encounter Milky Way’s Supermassive Black Hole
“The largest, closest single mass to Earth is Sagittarius A*, our Milky Way’s supermassive black hole, weighing in at 4,000,000 solar masses.
The star S0-2 makes the closest known approach to this black hole, reaching a minimum distance of just 18 billion kilometers.
That’s only three times the Sun-Pluto distance, or a meager 17 light-hours.”
After a 16 year wait, the closest star to the Milky Way’s supermassive black hole, S0-2, will make its closest approach later this year. At its closest, it should be moving at a whopping 2.5% the speed of light, enabling us to test out Einstein’s relativity in an entirely new regime. We should, for the first time, be able to measure the gravitational redshift from our galactic center, and to track the relativistic “kick” that Einstein’s theory predicts when an orbit gets modified by traveling close to an extremely large mass. New studies have recently shown that S0-2 doesn’t appear to have a binary companion, which makes it even more interesting for such an observation, which won’t come again until the year 2034. As a bonus, scientists hope to shed light on how stars form in the harsh environment of the galactic center at all.
Come find out how the newest test of Einstein could push us past the limits of relativity, or confirm it in an entirely new way!
Black Holes Must Have Singularities, Says Einstein’s Relativity
“The thing is, there’s a speed limit to how fast these force-carriers can go: the speed of light. If you want an interaction to work by having an interior particle exert an outward force on an exterior particle, there needs to be some way for a particle to travel along that outward path. If the spacetime containing your particles is below the density threshold necessary to create a black hole, that’s no problem: moving at the speed of light will allow you to take that outward trajectory.
But what if your spacetime crosses that threshold? What if you create an event horizon, and have a region of space where gravity is so intense that even if you moved at the speed of light, you couldn’t escape?”
Usually, when physicists first start teaching about black holes, the attitude they’re met with is skepticism. People can accept that as you compress a large mass into a smaller and smaller volume, it gets harder to escape its gravitational pull. As you go from a star to a white dwarf to a neutron star, you have to move closer to the speed of light to leave it’s surface. If you go even denser, you’ll create an event horizon: a region of space where the gravitational pull is so strong that nothing, not even light can escape. People are okay with that, but when you go to the next step and declare that anything that crosses the event horizon eventually falls into a central singularity, suddenly they’re not okay. Why, they reason, couldn’t there be some denser, exotic, degenerate form of matter than what we presently know? Why couldn’t that lie inside a black hole, rather than a singular point or ring? It’s a good question and an interesting bit of intuition, but there’s an answer for that.
If you wanted to hold anything up against collapse to a singularity inside a black hole, the force-carriers governing the interaction would have to travel faster than light, which is a no-go. Find out the full story on why black holes must have singularities!
The Three Meanings Of E=mc^2, Einstein’s Most Famous Equation
“Even masses at rest have an energy inherent to them. You’ve learned about all types of energies, including mechanical energy, chemical energy, electrical energy, as well as kinetic energy. These are all energies inherent to moving or reacting objects, and these forms of energy can be used to do work, such as run an engine, power a light bulb, or grind grain into flour. But even plain, old, regular mass at rest has energy inherent to it: a tremendous amount of energy. This carries with it a tremendous implication: that gravitation, which works between any two masses in the Universe in Newton’s picture, should also work based off of energy, which is equivalent to mass via E = mc^2.”
When it comes to equations, few can lay claim to being ‘the most famous one’ of all time, but right up there is Einstein’s greatest and simplest: E = mc^2. Yet it doesn’t simply state that mass and energy are equivalent, or that the relationship between them is given by the constant c^2. Sure, it says those things, but there’s also a vital physical meaning behind them. Understanding E = mc^2 has led to a variety of tremendous discoveries and breakthroughs, from nuclear power to the creation of new particles in particle accelerators. It even led directly to discovering that Newtonian gravity was theoretically unsound, ushering in the era of General Relativity, as well as the fact that any theory of gravity needs to include a gravitational redshift/blueshift.
How did it all come about? Find out the three meanings of Einstein’s most famous equation, and what it means for our Universe.
LIGO’s Greatest Discovery Almost Didn’t Happen
“If all we had done was look at the automated signals, we would have gotten just one “single-detector alert,” in the Hanford detector, while the other two detectors would have registered no event. We would have thrown it away, all because the orientation was such that there was no significant signal in Virgo, and a glitch caused the Livingston signal to be vetoed. If we left the signal-finding solely to algorithms and theoretical decisions, a 1-in-10,000 coincidence would have stopped us from finding this first-of-its-kind event. But we had scientists on the job: real, live, human scientists, and now we’ve confidently seen a multi-messenger signal, in gravitational waves and electromagnetic light, for the very first time.”
Imagine the scene: it’s mid-August, 2017, and the Virgo detector has just joined the twin LIGO detectors barely two weeks ago. Amazingly, on August 14th, you’ve seen a gravitational wave signal in all three detectors; another black hole-black hole merger. Then, all of a sudden, even though the LIGO detectors are set to shut down later in the month, an extraordinarily significant signal goes off… but only in one detector. The LIGO Hanford detector sees a signal with a false-alarm probability of just one part in 300 billion; a slam dunk. Yet both LIGO Livingston and Virgo see nothing. A non-coincident signal should automatically be rejected, but somehow, one of the young researchers working on the project thought to check the Livingston data by hand… and that was where the secret lay.
LIGO’s greatest discovery, of two merging neutron stars, almost was overlooked. Thankfully, the hands-on nature of the scientists working on gravitational waves were able to turn this into the discovery of the century! (So far!)