In February 1919, Royal Greenwich Observatory astronomer Frank Dyson and Cambridge University astronomer Arthur Eddington arranged for two teams of astronomers to observe and photograph a solar eclipse that would occur in May of that year as it moved across South America, the Atlantic Ocean, and Africa. One squad was headquartered in Sobral, Brazil, and the other off the coast of Africa on the little island of Principe.
The trips were designed to test Albert Einstein’s general theory of relativity. The hypothesis was divided and controversial within the scientific community at the time, having been published in 1915 after years of mathematical trial and error.
One of general relativity’s predictions was that light going through an object like the sun will appear to bend. Astronomical bodies, according to Einstein’s theory, would deform space-time because to their vastness, causing even light waves, which move at the absolute cosmic speed limit of 186,000 miles per second (300,000 kilometers per second) and in perfectly straight lines, to distort.
Astronomers were able to view the stars that appear nearest to the sun from Earth’s perspective due to the eclipse’s darkness, since they would otherwise be entirely wiped out by our star’s brilliance.
The task was completed successfully. They compared photographs of the Hyades, a cluster of stars in the constellation Taurus, with reference shots of the same cluster taken at night to assess any potential differences caused by the sun’s presence.
Dyson and Eddington both declared in November of that year that their findings backed up the notion. The naysayers were silenced, and Einstein and his work were thrust into the limelight.
General relativity is without a doubt one of the most profound scientific discoveries that humanity has ever made about the cosmos. Physicist J.J. Thomson allegedly described Einstein’s theory as “a whole continent of scientific ideas” when Eddington and Dyson published their findings.
The topography of the continent is still being studied by scientists. The idea addresses a number of strange physical manifestations, including the twisting of light around enormous celestial objects.
If the notions described by general relativity have ever bewildered you, you’re not alone—the theory fundamentally latches mankind into the reality that space is bending and the cosmos is strange. While an unflattering technical statement, that is the fundamental fact of the environment in which everyone and everything lives.
The simplest explanation is that the mass of an item is proportional to its gravitational pull. The gravitational force increases with mass, and the larger the force, the more space distortion happens. The interesting thing to remember is that gravity’s effects are the observable outcome of the fabric of space-time being distorted.
When you drop a stone from the top of a skyscraper, it follows the bending of space to the bottom rather than freefalling through a stable matrix of space.
This is when things start to get weird. Massive cosmic bodies bend time because the fabric is made up of four dimensions—three of space and one of time. The two are closely intertwined, which is why the term “space-time” was coined.
Returning to our marble. Due to the curvature of space, if put in Earth’s orbit, the stone will descend toward the planet’s surface. Time, however, is a dimension of that marble’s location, as we’ve shown. The curvature of time drives the marble ahead in time as the curvature of space draws it physically closer to the earth.
The essence of space is time.
Professor Eric Poisson is a theoretical physicist and the chair of the University of Guelph’s Department of Physics in Ontario, Canada. His research has aided our understanding of some of the universe’s most enigmatic celestial entities, including as black holes, neutron stars, and the gravitational waves they emit.
Source: Unsplash/Robson Hatsukami Morgan
In an interview with Interesting Engineering, Dr. Poisson described how, due to the effects of general relativity, time does not always flow in the same direction, and that this holds true even when measured at various locations on Earth.
“Einstein learned early on that if two clocks are moving relative to one other, they will tick at different speeds. The second lesson he gave us was that relative movements between clocks are not the same as relative location in a gravitational field. As a result, a clock deep within a gravitational field would operate slowly compared to a clock far away from any gravitational sources.
This is why, for example, a clock ticking away on Mount Everest will measure time differently from one ticking away at sea level, with the clock on the mountaintop ticking somewhat quicker than the one at sea level.
Most clocks, however, aren’t sensitive enough to detect this variation, which is measured in millionths of a second. While this may appear to be a charming, game-show-worthy science fact, it actually demonstrates how general relativity influences our everyday lives.
“Clocks in orbit are used in the GPS system,” Poisson continued. “Timestamps received via radio waves are calculated to show a place on Earth. We have a slew of ticking clocks in space, all ticking at various speeds and ticking at different rates than clocks on Earth. I
If we weren’t aware of the [temporal] difference caused by gravity, we’d discover the entire system isn’t functioning properly. On a daily level, it’s a really basic part of gravity for us.”
Binary black holes and gravitational waves
Poisson and other astrophysicists are currently experimenting with general relativity in novel ways. The Canadian Association of Physicists awarded him the Herzberg Medal in 2005 for his research on black holes and the gravitational waves they emit.
We now have a greater understanding of the interior workings of black holes, the most perplexing phenomenon in the observable universe, thanks to his work and that of his old doctoral adviser Werner Israel.
Einstein predicted gravitational waves in 1916, and the LIGO Scientific Collaboration, a group of scientists devoted to detecting and using the waves as a new tool to understand the cosmos, discovered them for the first time in 2015.
The role of Poisson in identifying these waves has been critical. He spent three years in the early 1990s working under Kip Thorne, one of the original members of LIGO, who, together with Rainer Weiss and Barry C. Barish, was awarded the Nobel Prize in Physics in 2017. Poisson’s method of solving perturbative gravitational wave equations numerically is an important aspect of the analysis utilized by LIGO to discover their presence.
Simply said, gravitational waves are minute ripples in the fabric of space-time caused by enormous entities such as black holes and neutron stars moving across it. Scientists now have the capacity to measure such waves, which entails the displacement of very sensitive laser beams, as LIGO revealed when their findings were published in the journal Physical Review Letters.
“We’re aiming to put gravitational wave detectors into orbit in the 2030s,” says the researcher.
“Measuring [them] is the biggest issue,” Poisson added. “The difficult issue is that they’re so little.” Laser beams are essentially used. When a gravitational wave travels across two freely moving objects in space, the distance between them begins to oscillate. What you can do is measure the relative distance between the two masses using a laser beam.”
“We anticipate being able to deploy gravitational wave detectors into orbit in the 2030s.” We’re optimistic that it will happen in the next 20 years.”
Poisson is particularly enthusiastic about the idea of gravitational waves revealing some of the universe’s deepest secrets. “We now live in a world where gravitational waves are used in astronomy,” he stated. “We’re learning about the cosmos in a whole new way.”
Poisson grew passionate as he explained why this is important. “When we look at the cosmos via visible light, for example, we perceive certain things. We saw a cosmos that was substantially different from what we had seen previously when we opened up the electromagnetic spectrum to start detecting radio waves. The visible cosmos was quite peaceful; nothing changed significantly during a human period, while radio wavelengths, X-rays, and gamma waves reveal a very agitated universe.”
Another glimpse into that cosmos is gravitational waves. This time, though, it’s a portal to the dark corners of the cosmos about which we know very little.
“The lesson was that whenever you open a new window into the cosmos, such as gravitational waves, you see something radically different.” We’re now looking at the black universe. Gravitational waves are created in locations where there is very little light. We observe black hole mergers, neutron star mergers, and other phenomena that we couldn’t see otherwise. The potential of gravitational waves is that.”
This is one of the most encouraging tools for Poisson to obtain a perspective on the history of some of the universe’ greatest entities. Binary systems are made up of black holes and neutron stars that orbit one other at extraordinary speeds, causing gravitational vibrations throughout the cosmos. The goal is that studying those waves would reveal more about how those systems came to be.
“That’s a significant thing in astrophysics.” Poisson argues, “[Gravitational waves] truly inform star development.”
Friends may have lit up your social media account in 2015 when gravitational waves were first discovered, but it’s doubtful that they’ve continued to pique your interest as you go about your daily routine. For the general public, significant scientific discoveries, particularly in the realm of astronomy, might seem quite fleeting.
Dr. Poisson freely admitted that this study is simply the notion of delayed gratification carried to its utmost maximum when asked how to encourage the public to care more about things like gravity waves and cosmic events with which they would never have any connection.
“We cannot keep mankind in the dark about these critical issues.”
“We’re not going to save lives or discover technologies that will make our lives better any time soon,” he said. “However, I believe that thinking about our position in the cosmos, thinking about what’s out there on the grandest proportions, understanding where we are and where we came from are fundamental questions that all of humanity has been asking throughout history.”
The fact that gravitational waves were discovered over 100 years after their prediction demonstrates the importance of patience and consistency in scientific study, which Poisson believes we should promote.
He underlined, “We cannot keep mankind in the dark regarding those extremely crucial matters.” “We may discover that answering such questions will take a very long period, but as mankind, we must continue to ask them.”
We’re getting closer to such answers because to the scholarship and devotion of people like Poisson and his scientific forefathers and contemporaries. May they be as enthralling as the cosmos has proved itself to be thus far.