Roger Penrose used mathematics to show black holes actually exist. Andrea Ghez and Reinhard Genzel helped uncover what lies at the center of our galaxy.
- Half of the prize was awarded to Roger Penrose, a British mathematical physicist who proved that black holes ought to exist, if Einstein's relativity is correct.
- The other half was awarded to Reinhard Genzel, a German astrophysicist, and Andrea Ghez, an American astronomer.
- Genzel and Ghez helped develop techniques to capture clearer images of the cosmos.
Sagittarius A*<p>Since the early 1990s, Genzel and Ghez have been leading independent teams of astronomers that have helped develop techniques for capturing clearer images of the cosmos from Earth. The teams' primary focus of study was what lies at the center of our galaxy, a region called Sagittarius A*. </p>
Credit: Johan Jarnestad/The Royal Swedish Academy of Sciences<p>Using some of the world's most sophisticated telescopes, Genzel and Ghez also discovered that one star in this region, known as S2 or S-O2, orbits the galaxy's center in just 16 years. (Compare that to our Sun, which takes 200 million years to complete an orbit around the galaxy.) Measurements from both teams indicated that Sagittarius A* is about the size of our solar system, but is incredibly dense, containing roughly 4 million solar masses. This led them to conclude the center of our galaxy could be only one thing: a supermassive black hole. </p>
Grandfathers, take heart. You'll survive the paradox that's been gunning for you since the 1930s.
A paradox primer<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDQ1MzcyOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY2OTkwMTE3Mn0.3dY_kFWg3zsmLrnKHEz7NPWdiJYBgJUUQa_dJZ21p9A/img.jpg?width=1245&coordinates=0%2C75%2C0%2C75&height=700" id="7f1c4" class="rm-shortcode" data-rm-shortcode-id="9ca569af0bbe83100698d67202e4bcbf" data-rm-shortcode-name="rebelmouse-image" data-width="1245" data-height="700" />
According to the study, the universe would have worked things out whether Marty stole credit for "Johnny B. Goode" or not.
(Photo: Universal Studios)<p>The classic temporal thought experiment is known as <a href="https://www.space.com/grandfather-paradox.html#:~:text=The%20grandfather%20paradox%20is%20a%20potential%20logical%20problem%20that%20would,make%20their%20own%20birth%20impossible." target="_blank">the grandfather paradox</a>. It goes like this: Imagine you decide to go back in time to kill your grandfather. Yes, his election-year posts have been that embarrassing. You travel back and kill him before he conceives one-half of your parents. But then, how is it you can exist to go back and kill him? But if you don't exist, then who killed your grandfather? <a href="https://bigthink.com/paul-ratner/neil-degrasse-tyson-explains-the-strange-paradoxes-of-time-travel" target="_self">Paradox</a>. The timeline is no longer self-consistent. (<a href="https://www.youtube.com/watch?v=XayNKY944lY" target="_blank">Maybe</a>.)</p><p>You can play this game with most time traveling tales. In "<a href="https://www.imdb.com/title/tt0088763/" target="_blank" style="">Back to the Future</a>," Marty travels back in time and interferes with his parents' dalliance, preventing himself from being born. But if Marty is never born, how does he interfere with his parents' dalliance? But if he can't interfere, what's preventing him from being born? And round we go.</p><p>One would think such worries limited to high-minded philosophy debates or low-brow movie riffs. But some solutions to Einstein's field equations allow time travel through <a href="https://www.thegreatcoursesdaily.com/did-einstein-prematurely-reject-godels-universe/#:~:text=A%20closed%20timelike%20curve%20is,encounter%20the%20same%20event%20again." target="_blank" rel="noopener noreferrer">closed timelike curves</a>. These theoretical paths would allow someone to be present at an initial event, travel through space and time, and return to that event again. Think a spacetime loop-the-loop. Importantly, the return point is not a repeat of the initial event. It is the initial event.</p><p>The implications of closed timelike curves lead to all sorts of wild time travel scenarios. <a href="https://bigthink.com/dr-kakus-universe/is-time-travel-possible" target="_self">According to physicist Michio Kaku</a>, these have included traveling through a wormhole, through a spinning black hole, around an infinitely-long spinning cylinder, and around two colliding cosmic strings.</p>
The universe is a self-regulating Time Lord<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yNDQ1MzczNC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzMTQ2NTA3Mn0.QawOiC0smajTijNpoJbY1UsnB4VhoRGds5swcKdowW8/img.jpg?width=1245&coordinates=0%2C51%2C0%2C51&height=700" id="d0230" class="rm-shortcode" data-rm-shortcode-id="93e944fc3f902cadf33e6e7211efc84d" data-rm-shortcode-name="rebelmouse-image" data-width="1245" data-height="700" />
Dr. Fabio Costa (left) and Germain Tobar (right) discuss their findings. Behind them, a process function (w) interacts with localized spacetime regions with closed timelike curves.
Credit: University of Queensland<p>With time travel on the theoretical table, Tobar Germain, a University of Queensland undergraduate, wanted to test its consistency. Is paradox-free time travel mathematically possible? To answer that question, he teamed up with Dr. Fabio Costa, a University of Queensland physicist, to crunch the numbers.</p><p>"Some physicists say it is possible, but logically, it's hard to accept because that would affect our freedom to make any arbitrary action," Tobar said <a href="https://www.uq.edu.au/news/article/2020/09/young-physicist-squares-numbers%E2%80%99-time-travel" target="_blank">in a release</a>. "It would mean you can time travel, but you cannot do anything that would cause a paradox to occur."</p><p>According to their research, time travel can be consistent and free of logical paradoxes. However, that requires the outputs of all but two space-time regions to be fixed. In that case, despite the presence of closed timelike loops, entities can maintain their freedom of choice without resulting in a paradox.</p><p>"The maths checks out, and the results are the stuff of science fiction," Costa said in the same release.</p><p>To illustrate their findings, Tobar and Costa offer a thought experiment straight out of science fiction. Imagine you travel through time to stop the COVID-19 pandemic. You locate and quarantine patient zero. Mission (and paradox) accomplished, right? Not according to their research. The math suggests that temporal events would adjust to being logically consistent with any action you made. For example, you may catch the virus, become patient zero, and spread the pandemic anyway. </p><p>Therefore, future, erm, past you still has the stimulus that sent you back in time initially.</p><p>"No matter what you did, the salient events would just recalibrate around you," Tobar said. "That would mean that—no matter your actions—the pandemic would occur, giving your younger self the motivation to go back and stop it.</p><p>"The range of mathematical processes we discovered show that time travel with free will is logically possible in our universe without any paradox."</p>
Riding the timelike curve?<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="26aeff2dbb93f6414170073a6f60c870"><iframe type="lazy-iframe" data-runner-src="https://www.youtube.com/embed/6yMiUq7W_xI?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p>Of course, sayings paradox-free time travel is mathematically consistent is a wildly different statement than saying it is practically possible. Even if you could take the plunge into <a href="https://www.scientificamerican.com/article/the-chronology-protection/" target="_blank" rel="noopener noreferrer">a wormhole</a>, there's a good chance you'd be crushed out of existence before reaching the other end. Souped-up DeLorean or no. </p><p>It all depends on how the <a href="https://bigthink.com/surprising-science/physicist-radical-theory-of-gravity" target="_self">laws of quantum gravity</a> shake out, and physicists are still exploring that very open question. What about those other scenarios Kaku pointed out? In <a href="https://bigthink.com/dr-kakus-universe/is-time-travel-possible-part-ii" target="_self">a follow-up article</a>, he points out that none can be realized using known physical mechanisms.</p><p>So, while we may be the time lords of the whiteboard, the universe will be a one-way street for the foreseeable future.</p>
Math doesn't suck. It is one of humanity's greatest and most mysterious journeys.
- There is a pervasive cultural attitude against mathematics, but it is actually a mind-blowing tool for analyzing and predicting the world around us—and far beyond. We asked mathematicians Edward Frenkel and Po-Shen Loh, and physicists Michio Kaku, Michelle Thaller, Janna Levin and Geoffrey West to explain the wonders of math.
- West explains the rule of 'quarter-power scaling' in biology—there is a mathematical equation that predicts how much food an organism needs to eat to survive and it's remarkably consistent, whether you're looking at ladybugs, cats, elephants, and even trees and flowers. Math underpins our lives in incredible ways.
- Infinitesimal calculus—the math that describes how moving bodies change over time—turns out to predict not just phenomena on Earth but far out in the universe. The 11-dimensional math used by physicists turns out to predict the exact results of particle physics experiments. Humanity is on an incredible journey with mathematics and every day it opens up the world and universe in eye-opening ways.
The outer edges of a black hole might be "fuzzy" instead of neat and smooth.
- A recent study analyzed observations of gravitational waves, first observed in 2015.
- The data suggests, according to the researchers, that black holes aren't bounded by smooth event horizons, but rather by a sort of quantum fuzz, which would fit with the idea of Hawking radiation.
- If confirmed, the findings could help scientists better understand how general relativity fits with quantum mechanics.
ESO, ESA/Hubble, M. Kornmesser<p>In the 1970s, Stephen Hawking famously proposed that black holes aren't truly "black." In simplified terms, the theoretical physicist reasoned that, due to quantum mechanics, black holes actually emit tiny amounts of black-body radiation, and therefore have a non-zero temperature. So, contrary to Einstein's view that black holes are neatly defined and are not surrounded by loose materials, Hawking radiation suggests that black holes are actually surrounded by quantum "fuzz" that consists of particles that escape the gravitational pull.</p><p>"If the quantum fuzz responsible for Hawking radiation does exist around black holes, gravitational waves could bounce off of it, which would create smaller gravitational wave signals following the main gravitational collision event, similar to repeating echoes," Afshordi said.</p>
Credit: NASA's Goddard Space Flight Center/Jeremy Schnittman<p>A new study from Afshordi and co-author Jahed Abedi could provide evidence of these signals, called gravitational wave "echoes." Their analysis examined data collected by the <a href="http://www.virgo-gw.eu/" target="_blank">LIGO and Virgo gravitational wave detectors</a>, which in 2015 detected the first direct observation of gravitational waves from the collision of two distant neutron stars. The results, at least according to the researchers' interpretation, showed relatively small "echo" waves following the initial collision event.</p><p>"The time delay we expect (and observe) for our echoes ... can only be explained if some quantum structure sits just outside their event horizons," Afshordi told <em><a href="https://www.livescience.com/black-hole-echoes-unsettle-einstein-relativity.html" target="_blank">Live Science</a>.</em></p>
Afshordi et al.<p>Scientists have long studied black holes in an effort to better understand fundamental physical laws of the universe, especially since the introduction of Hawking radiation. The idea highlighted the extent to which general relativity and quantum mechanics conflict with each other. </p><p>Everywhere — even in a vacuum, like an event horizon — pairs of so-called <a href="https://www.scientificamerican.com/article/something-from-nothing-vacuum-can-yield-flashes-of-light/" target="_blank">"virtual particles"</a> briefly pop in and out of existence. One particle in the pair has positive mass, the other negative. Hawking imagined a scenario in which a pair of particles emerged near the event horizon, and the positive particle had just enough energy to escape the black hole, while the negative one fell in.</p><p>Over time, this process would lead black holes to evaporate and vanish, given that the particle absorbed had a negative mass. It would also lead to some interesting <a href="https://en.wikipedia.org/wiki/Black_hole_information_paradox#Recent_developments" target="_blank">paradoxes</a>.</p><p>For example, quantum mechanics predicts that particles would be able to escape a black hole. This idea suggests that black holes eventually die, which would theoretically mean that the physical information within a black hole also dies. This violates a key idea in quantum mechanics which is that physical information can't be destroyed.</p><p>The exact nature of black holes remains a mystery. If confirmed, the recent discovery could help scientists better fuse these two models of the universe. Still, some researchers are skeptical of the recent findings.</p><p>"It is not the first claim of this nature coming from this group," Maximiliano Isi, an astrophysicist at MIT, <a href="https://www.livescience.com/black-hole-echoes-unsettle-einstein-relativity.html" target="_blank">told</a> Live Science. "Unfortunately, other groups have been unable to reproduce their results, and not for lack of trying."</p><p>Isi noted that other papers examined the same data, but failed to find echoes. Afshordi told <em>Galaxy Daily</em>:</p><p>"Our results are still tentative because there is a very small chance that what we see is due to random noise in the detectors, but this chance becomes less likely as we find more examples. Now that scientists know what we're looking for, we can look for more examples, and have a much more robust confirmation of these signals. Such a confirmation would be the first direct probe of the quantum structure of space-time."</p>
From talking about Schrödinger's cat to nuking the South Pole, this decades-old interview shows why Kaku was born to be a science educator.
- Michio Kaku is a theoretical physicist and renowned science communicator.
- In 1991, he sat down for an hour-long interview in which he discussed climate change, nuclear weapons, human evolution, and more.
- Kaku is a regular contributor to Big Think.