Category: relativity

The Three Meanings Of E=mc^2, Einstein’s…

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.

Ask Ethan: How Do Hawking Radiation And Relati…

Ask Ethan: How Do Hawking Radiation And Relativistic Jets Escape From A Black Hole?

“Everything you read about a black indicates that “nothing, not even light, can escape them”. Then you read that there is Hawking radiation, which “is blackbody radiation that is predicted to be released by black holes”. Then there are relativistic jets that “shoot out of black holes at close to the speed of light”. Obviously, something does come out of black holes, right?”

When it comes to black holes, the cardinal rule is that there exists an event horizon: a region from which nothing inside can ever escape. Once you cross over, you can never get out. No matter how fast you move, how quickly or what direction you accelerate in, or even if you travel at the speed of light, your inevitable destiny lies at the central singularity. So how, then, are things like relativistic jets and Hawking radiation emitted from black holes? The key to understanding them lies in examining the conditions that occur outside the event horizon, in the region near (but not exactly at) the black hole itself. This is the critical environment where spacetime is curved, matter achieves relativistic speeds, and the quantum fields themselves are affected by relativity.

Hawking radiation and relativistic jets may be real, but they don’t break the laws of physics to exist! Find out how they really do escape on this edition of Ask Ethan.

Black holes, like the collapse of a cavity in …

Black holes, like the collapse of a cavity in a fluid, are a singularity – a point where the mathematical rules we use to describe physical systems break down. No one knows what exists in a black hole, but the short film “Intra” explores one theory – that the exit to a black hole is a white hole, a singularity from which time and space themselves are born. The journey from one to the other is illustrated in the film with CGI visualizations of a black hole (a la Interstellar) and with fluid dynamical sequences depicting diffusion and chemical reactions driving flows. Although no true white holes have ever been observed, there are fluid dynamical analogs for them, namely circular hydraulic jumps, like the one you can make in your kitchen sink!  (Video credit: T. Vanz et al.)

Richard Feynman And John Wheeler Revolutionized Time, Reality,…

Richard Feynman And John Wheeler Revolutionized Time, Reality, And Our Quantum Universe

“Yet at their core, these two were practically tailor-made to collaborate with one another. Wheeler’s wild ideas always contained components that were spectacularly wrong and unworkable, but often contained a kernel of deep truth that would pave the road to an understanding that was otherwise unachievable. The idea of a path integral, the essential tool used to calculate physical observables in quantum field theory, came about from Wheeler’s insistence on a sum over histories, but it was Feynman who worked out the details correctly, and applied them properly to our physical Universe.

Feynman’s ability to connect the wild ideas to the physical Universe, never far afield from what could be measured, was the perfect complement to Wheeler’s imagination. Together and separately, they took on gravitation, the quantum nature of reality, and even space and time itself. And as much as any physicist ever did, they not only took these ideas on; they won.”

In popular culture, Richard Feynman is revered as a non-conformist/genius, whose bongo-playing, carefree antics are as notable as his groundbreaking physics research. John Wheeler, renowned for his contributions to General Relativity, gravitation, and information theory, has no similar stories from his personal lives. Yet professionally, these two complemented one another in ways that were unimaginable to an outside onlooker: Wheeler’s imagination ran wildly into the speculative and unworkable, while Feynman was always dragging things back to observable and measurable quantities. In the end, both are remembered as towering figures in physics in the 20th century, on par with names like Bohr, Dirac, Pauli, and Heisenberg. In a sweeping new book, Paul Halpern takes an in-depth look at the scientific and personal lives of these two physicists, who first met in 1939 and spent the next five decades revolutionizing our conception of the Universe.

Get the full book review here, and if you’re at all interested in picking up a copy for yourself (or the physics enthusiast in your life), follow the links and go get a copy of The Quantum Labyrinth! 

How Traveling Back In Time Could Really, Physically Be…

How Traveling Back In Time Could Really, Physically Be Possible

“Satisfyingly, we discover that this form of time travel also forbids the grandfather paradox! Even if the wormhole were created before your parents were conceived, there’s no way for you to exist at the other end of the wormhole early enough to go back and find your grandfather prior to that critical moment. The best you can do is to put your newborn father and mother on a ship to catch the other end of the wormhole, have them live, age, conceive you, and then send yourself back through the wormhole. You’ll be able to meet your grandfather when he’s still very young — perhaps even younger than you are now — but it will still, by necessity, occur at a moment in time after your parents were born.”

So, you want to travel back in time? It’s long been considered as a trope in science fiction movies, television, and literature, but the laws of physics make traveling backwards through time very difficult. In special relativity, it’s impossible, as you can only control the rate you move forward through time; the direction is non-negotiable. But in General Relativity, the curvature of space and time opens up additional possibilities. You can create a stable, traversible wormhole if some type of negative mass/energy exists, with a supermassive black hole connected to its negative mass/energy counterpart. Now, move one end of that wormhole close to the speed of light, and the two mouths age at different rates. Travel through the fast-moving end, and discover you’re back at the stationary end way in the distant past… but still in the future compared to when the wormhole was created.

It’s a brilliant way to achieve time travel, and as a bonus, it makes it impossible to go back in time and kill your own grandfather before you were conceived! Come learn how time travel could really, physically be possible after all.

Five Discoveries In Fundamental Physics That Came As Total…

Five Discoveries In Fundamental Physics That Came As Total Surprises

“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”

It’s often said that advanced in physics aren’t met with “eureka!” but rather with “that’s funny,” but the truth is even stranger sometimes. Rather than the scientific method of: hypothesis, method, experiment, results, conclusion, revise, repeat, etc., many times throughout history, it’s been a series of surprise observations that have often led to our greatest leaps forward. When the speed of light was discovered not to differ when you moved with or against it, it was so revolutionary it was the only Nobel Prize ever awarded for a null result. When the gold foil experiment resulted in high-energy recoils, it surprised Rutherford so thoroughly it was the most incredible thing to ever happen to him in his life. The leftover glow from the Big Bang was discovered quite by accident; the neutrino was a crazy hypothesis that many abandoned; and the discovery of the muon, perhaps the most unexpected particle of all, literally was met with a cry of, “who ordered that?” from Nobel Laureate I.I. Rabi.

These five discoveries changed the course of physics forever, but they came as total surprises to practically everyone. Sometimes, the answer is in the place you least expect.

Astronomy’s ‘Rosetta Stone’: Merging Neutron…

Astronomy’s ‘Rosetta Stone’: Merging Neutron Stars Seen With Both Gravitational Waves And Light

“For the first time in history, gravitational wave astronomy isn’t a pipe dream, nor is it a way of looking for esoteric objects we can’t see via any other means. Instead, it’s truly a part of our night sky, and the first signpost of an astronomical cataclysm. In the future, as gravitational wave astronomy improves, it may even serve as an early warning system, enabling us to locate sources about to merge before they ever do so. It may grow to include not only black holes and neutron stars, but white dwarfs and supermassive black holes swallowing objects as well. Gravitational wave astronomy is only two years old, and we haven’t even taken it to space yet. The next step in understanding the Universe is before us. Sit back and enjoy the ride!”

When the Advanced LIGO detectors turned on in 2015, it shook up the world when they detected their first event: the merger of two quite massive black holes. Since that time, they’ve observed black hole-black hole mergers multiple times, with the VIRGO detector in Italy joining them for the fourth event. But this wasn’t what LIGO/VIRGO expected to see; rather, they were built to hunt for merging neutron stars that were much closer by. Neutron star mergers would be superior to black hole mergers in an extraordinary way: it would enable other astronomers to get in on the action. Unlike black holes, merging neutron stars should emit radiation across the electromagnetic spectrum, from gamma-rays to UV/optical afterglows. On August 17th, LIGO and VIRGO saw their very first neutron star merger, pinpointing its location to galaxy NGC 4993, just 120 million light years away.

For the first time, we’ve joined the gravitational wave and light-based skies together with an incredible event. It’s a glorious step forward. And it’s just the beginning.

Gravitational Waves Win 2017 Nobel Prize In Physics, The…

Gravitational Waves Win 2017 Nobel Prize In Physics, The Ultimate Fusion Of Theory And Experiment

“The 2017 Nobel Prize in Physics may have gone to three individuals who made an outstanding contribution to the scientific enterprise, but it’s a story about so much more than that. It’s about all the men and women over more than 100 years who’ve contributed, theoretically and experimentally and observationally, to our understanding of the precise workings of the Universe. Science is much more than a method; it’s the accumulated knowledge of the entire human enterprise, gathered and synthesized together for the betterment of everyone. While the most prestigious award has now gone to gravitational waves, the science of this phenomenon is only in its earliest stages. The best is yet to come.”

It’s official at long last: the 2017 Nobel Prize in Physics has been awarded to three individuals most responsible for the development and eventual direct detection of gravitational waves. Congratulations to Rainer Weiss, Kip Thorne, and Barry Barish, whose respective contributions to the experimental setup of gravitational wave detectors, theoretical predictions about which astrophysical events produce which signals, and the design-and-building of the modern LIGO interferometers helped make it all possible. The story of directly detecting gravitational waves is so much more, however, than the story of just these three individuals, or even than the story of their collaborators. Instead, it’s the ultimate culmination of a century of theoretical, experimental, and instrumentational work, dating back to Einstein himself. It’s a story that includes physics titans Howard Robertson, Richard Feynman, and Joseph Weber. It includes Russell Hulse and Joseph Taylor, who won a Nobel decades earlier for the indirect detection of gravitational waves. And it’s the story of over 1,000 men and women who contributed to LIGO and VIRGO, bringing us into the era of gravitational wave astronomy.

The 2017 Nobel Prize in Physics may only go to three individuals, but it’s the ultimate fusion of theory and experiment. And yes, the best is yet to come! 

5 Facts We Can Learn If LIGO Detects Merging Neutron Stars “We…

5 Facts We Can Learn If LIGO Detects Merging Neutron Stars

“We have already entered a new age in astronomy, where we’re not just using telescopes, but interferometers. We’re not just using light, but gravitational waves, to view and understand the Universe. If merging neutron stars reveal themselves to LIGO, even if the events are rare and the detection rate is low, it’s means we’ll have crossed that next frontier. The gravitational sky and the light-based sky will no longer be strangers to one another. Instead, we’ll be one step closer to understanding how the most extreme objects in the Universe actually work, and we’ll have a window into our cosmos that no human has ever had before.”

Two years ago, advanced LIGO turned on, and in that brief time, it’s already revealed a number of gravitational wave events. All of them, to no one’s surprise, have been merging black holes, since those are the easiest class of events for LIGO to detect. But beyond black holes, LIGO should also be sensitive to merging neutron stars. Even though the range over which LIGO can see them is much smaller, if there are enough neutron star-neutron star mergers happening, we might have a chance. A little over a week ago, a rumor broke that LIGO may have seen one, which would be a phenomenal occurrence. Not only would we have a new type of event that we detected in gravitational waves, we would, for the first time, have the capability of correlating the gravitational and electromagnetic skies. Astronomy, for the first time ever, could view the very same object in gravitational waves and through telescopes.

This is a big deal, and there are four more facts we’ll learn if LIGO sees it! Come find out what they are!

Beyond Black Holes: Could LIGO Have Detected Merging Neutron…

Beyond Black Holes: Could LIGO Have Detected Merging Neutron Stars For The First Time?

“We are present at an incredible time in history: at the birth of the observational science of gravitational wave astronomy. The coming decades will reveal a series of “firsts,” and that should include the first binary neutron star merger, the first pinpointing of a gravitational wave source, and the first correlation between gravitational waves and an electromagnetic signal. If nature is kind to us, and the rumors are true, we may have just unlocked all three.”

It seems like an eternity ago, but it’s been under two years since LIGO first began the science run that would first detect merging black holes. Their latest scientific data run is scheduled to end in just two days, and thus far, they’ve announced a total of three black hole-black hole merger discoveries, along with a fourth probable candidate. Yet thanks to the Twitter account of renowned astrophysicist J. Craig Wheeler, a bit of information has leaked: LIGO may have discovered merging neutron stars for the first time. They’d be approximately ten times lighter than the black holes we’ve witnessed merging, which means the signals are only 10% as strong. In order to get the same amplitude, they’d need to be only 10% as distant, cutting the search volume down to 0.1% the volume. But still, neutron stars may be much more abundant, so we might have a chance. Just yesterday, Hubble observed a galaxy with a binary neutron star inside, just 130 million light years away.

Could we have just detected a merging neutron star pair for the first time, in both gravitational waves and electromagnetic radiation, together? The rush is on to find out!