Experts ask where the center of the universe is
This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.
About a century ago, scientists were struggling to reconcile what seemed a contradiction in Albert Einstein's theory of general relativity.
Published in 1915, and already widely accepted worldwide by physicists and mathematicians, the theory assumed the universe was static – unchanging, unmoving and immutable. In short, Einstein believed the size and shape of the universe today was, more or less, the same size and shape it had always been.
But when astronomers looked into the night sky at faraway galaxies with powerful telescopes, they saw hints the universe was anything but that. These new observations suggested the opposite – that it was, instead, expanding.
Scientists soon realized Einstein's theory didn't actually say the universe had to be static; the theory could support an expanding universe as well. Indeed, by using the same mathematical tools provided by Einstein's theory, scientists created new models that showed the universe was, in fact, dynamic and evolving.
I've spent decades trying to understand general relativity, including in my current job as a physics professor teaching courses on the subject. I know wrapping your head around the idea of an ever-expanding universe can feel daunting – and part of the challenge is overriding your natural intuition about how things work. For instance, it's hard to imagine something as big as the universe not having a center at all, but physics says that's the reality.
First, let's define what's meant by "expansion." On Earth, "expanding" means something is getting bigger. And in regard to the universe, that's true, sort of. Expansion might also mean "everything is getting farther from us," which is also true with regard to the universe. Point a telescope at distant galaxies and they all do appear to be moving away from us.
What's more, the farther away they are, the faster they appear to be moving. Those galaxies also seem to be moving away from each other. So it's more accurate to say that everything in the universe is getting farther away from everything else, all at once.
This idea is subtle but critical. It's easy to think about the creation of the universe like exploding fireworks: Start with a big bang, and then all the galaxies in the universe fly out in all directions from some central point.
But that analogy isn't correct. Not only does it falsely imply that the expansion of the universe started from a single spot, which it didn't, but it also suggests that the galaxies are the things that are moving, which isn't entirely accurate.
It's not so much the galaxies that are moving away from each other – it's the space between galaxies, the fabric of the universe itself, that's ever-expanding as time goes on. In other words, it's not really the galaxies themselves that are moving through the universe; it's more that the universe itself is carrying them farther away as it expands.
A common analogy is to imagine sticking some dots on the surface of a balloon. As you blow air into the balloon, it expands. Because the dots are stuck on the surface of the balloon, they get farther apart. Though they may appear to move, the dots actually stay exactly where you put them, and the distance between them gets bigger simply by virtue of the balloon's expansion.
Now think of the dots as galaxies and the balloon as the fabric of the universe, and you begin to get the picture.
Unfortunately, while this analogy is a good start, it doesn't get the details quite right either.
Important to any analogy is an understanding of its limitations. Some flaws are obvious: A balloon is small enough to fit in your hand – not so the universe. Another flaw is more subtle. The balloon has two parts: its latex surface and its air-filled interior.
These two parts of the balloon are described differently in the language of mathematics. The balloon's surface is two-dimensional. If you were walking around on it, you could move forward, backward, left, or right, but you couldn't move up or down without leaving the surface.
Now it might sound like we're naming four directions here – forward, backward, left and right – but those are just movements along two basic paths: side to side and front to back. That's what makes the surface two-dimensional – length and width.
The inside of the balloon, on the other hand, is three-dimensional, so you'd be able to move freely in any direction, including up or down – length, width and height.
This is where the confusion lies. The thing we think of as the "center" of the balloon is a point somewhere in its interior, in the air-filled space beneath the surface.
But in this analogy, the universe is more like the latex surface of the balloon. The balloon's air-filled interior has no counterpart in our universe, so we can't use that part of the analogy – only the surface matters.
So asking, "Where's the center of the universe?" is somewhat like asking, "Where's the center of the balloon's surface?' There simply isn't one. You could travel along the surface of the balloon in any direction, for as long as you like, and you'd never once reach a place you could call its center because you'd never actually leave the surface.
In the same way, you could travel in any direction in the universe and would never find its center because, much like the surface of the balloon, it simply doesn't have one.
Part of the reason this can be so challenging to comprehend is because of the way the universe is described in the language of mathematics. The surface of the balloon has two dimensions, and the balloon's interior has three, but the universe exists in four dimensions. Because it's not just about how things move in space, but how they move in time.
Our brains are wired to think about space and time separately. But in the universe, they're interwoven into a single fabric, called 'space-time.' That unification changes the way the universe works relative to what our intuition expects.
And this explanation doesn't even begin to answer the question of how something can be expanding indefinitely – scientists are still trying to puzzle out what powers this expansion.
So in asking about the center of the universe, we're confronting the limits of our intuition. The answer we find – everything, expanding everywhere, all at once – is a glimpse of just how strange and beautiful our universe is.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
Yahoo
22 minutes ago
- Yahoo
Astronomers discover giant alien planet 35 times more massive than Earth hiding in a known star system
When you buy through links on our articles, Future and its syndication partners may earn a commission. Scientists have detected a hidden alien planet by examining the orbits of the known worlds in the star system, known as Kepler-139. The newfound exoplanet, called Kepler-139f, is a gigantic world roughly twice the mass of Neptune and 35 times the mass of Earth, and it takes 355 days to orbit its star, astronomers reported in a study published May 2 in The Astrophysical Journal Letters. Despite its giant size, Kepler-139f had evaded detection. That's because the initial yield of NASA's Kepler space telescope, which discovered nearly 3,000 planets in its nine years of operation, relied on worlds transiting — passing between their star and Earth. The resulting dimming of the star allowed astronomers to identify planets and calculate their size. But Kepler couldn't see planets traveling above or below the wedge of space between it and the star, so any outliers remained unseen. But if the hidden world was part of a multiplanet system, astronomers could try to find it despite its inclined orbit. Kepler-139 has three rocky transiting super-Earths; a fourth gas giant was later discovered. Gaps in their orbits suggested that other worlds might be present. Precise measurements of the orbits allowed the astronomers to infer the existence of at least one more planet. "The issue is not exactly finding non-transiting planets, but rather, finding situations in which we can deduce where the non-transiting planet is located," Caleb Lammers, a graduate student in the Department of Astrophysical Science at Princeton and co-author of the study, told by email. Kepler's initial identification of a world was often followed up by observations from the ground. Using radial velocity (RV), astronomers could measure how much a planet tugged on its star, allowing them to determine the planet's mass. RV measurements could also reveal new worlds, as happened with the outermost gas giant, Kepler-139e. At the same time, each planet is pulled by not only its star but also by other planets in the system, regardless of whether that planet can be seen from Earth. These pulls can affect how swiftly a planet transits, thus creating "transit timing variations" (TTVs). These variations in the transiting planets can reveal worlds that don't cross the star. "When you observe TTVs that cannot be attributed to the known planets, you can be fairly confident that there is an unseen body in the system," Lammers said. Lammers and his colleague Joshua Winn, a participating scientist on the Kepler team and co-author of the study, went looking for gaps in known systems. Then, they used both RV and TTV measurements to hunt for a missing world, revising existing TTVs based on the 2023 discovery of Kepler-139e. "What was different in the case of Kepler-139 is that we had precise radial velocity observations which did not conclusively point towards a new planet on their own," Lammers said. Combined with the TTVs, the observations revealed a fifth planet, Kepler-139f, tucked between the outermost super-Earth and the gas giant. The new discovery also helped to answer a question about Kepler-139e. The original reports of Kepler-139c, the outermost super-Earth, provided an unusually large density for a sub-Neptune-size planet. The discrepancy occurred because those authors didn't know about Kepler139f, so they had attributed some of its pull on its star to Kepler-139c. The new data suggest a more typical density for Kepler-139c while leaving the densities for Kepler-139d and Kepler-139b essentially unchanged. These revisions provide indirect evidence for Kepler-139f, Lammers said. There may even be other hidden worlds around Kepler-139. "It remains possible that there are other unseen planets in the system," Lammers said, pointing to the prominent gap between planets b and c. "The challenge is finding them!" Both Kepler and NASA's more recent exoplanet hunting mission, the Transiting Exoplanet Survey Satellite (TESS), were sensitive to planets orbiting closer to their star. These inner worlds were more likely to make many transits, allowing scientists to confirm the planet's existence. But transiting planets with wider orbits made only a handful of passes, so they were more challenging to observe and confirm. At the same time, the RV method tends to be biased toward larger planets, because the more massive a world is, the stronger it tugs on its star. Proximity helps; the pull of the planet is amplified to the square inverse of its distance. Thus, a planet twice as far away will have only one-fourth the gravitational pull. That's why many of the first discovered exoplanets were Jupiter-size worlds that circled their star in only a few days. RELATED STORIES —Massive new NASA exoplanet catalog unveils 126 extreme and exotic worlds —25 years of exoplanet hunting hasn't revealed Earth 2.0 — but is that what we're looking for? —The 10 most Earth-like exoplanets All of these factors make it harder to discover smaller planets that are farther away, particularly if they don't transit their star. But by combining transits, RVs and TTVs, astronomers can find smaller, hidden worlds orbiting farther from their star. "It is likely that many planetary systems host unseen worlds, especially in their outer regions," Lammers said. But soon, it will be harder for those worlds to hide. In 2026, the European Space Agency will launch its Planetary Transits and Oscillations of Stars (PLATO) mission, which will conduct its own survey of transiting planets, as well as revisit Kepler's field. In providing additional transit times for planets detected by Kepler more than a decade later, PLATO will improve measurements of TTVs to enable the discovery of more misaligned worlds. "In the coming years, the TTV planet detection technique will probably be accelerated dramatically by the PLATO mission," Lammars said.
CBS News
an hour ago
- CBS News
What to know about the Perseids and when to view the 2025 meteor shower
The Perseids meteor shower begins this week and is expected to offer one of the best shows in the sky of 2025. The event is considered the best meteor shower of the year, according to NASA, and is also the most popular. The shower begins on Thursday, July 17, and will continue for several weeks, until at least Aug. 23, according to NASA and the American Meteor Society, a nonprofit organization. The meteor shower is expected to peak from Aug. 12-13, although moonlight will impact meteor visibility. The moon will be 84% full during the peak. NASA says the best time to view the Perseids is early in the morning, before dawn, in the Northern Hemisphere. Sometimes, however, the meteors can be seen at night as early as 10 p.m. "The Perseids are one of the most plentiful showers with about 50 to 100 meteors seen per hour," NASA says. "They occur with warm summer nighttime weather allowing sky watchers to comfortably view them." Perseids often leave long "wakes" of color and light when they move through Earth's atmosphere. NASA notes they are also known for their fireballs. "Fireballs are larger explosions of light and color that can persist longer than an average meteor streak," the space agency says. "This is due to the fact that fireballs originate from larger particles of cometary material. Fireballs are also brighter." The meteor shower occurs when Earth passes through an area of space debris left by a comet coming around the sun. Debris interacts with Earth's atmosphere and disintegrates, resulting in colorful lines in the sky, according to NASA and the American Meteor Society. "The pieces of space debris that interact with our atmosphere to create the Perseids originate from comet 109P/Swift-Tuttle," which last visited the inner solar system in 1992, NASA says. Swift-Tuttle takes 133 years to orbit the sun, NASA said, and in 1865, Italian astronomer Giovanni Schiaparelli became the first person to determine this comet was the source of the Perseids. When looking at the Perseids, they appear to come from the constellation Perseus, which is why this meteor shower has its name. But as NASA explains, the meteors don't actually originate from the constellation.
CBS News
5 hours ago
- CBS News
Largest-ever merger of black holes forms one 225 times the mass of the sun, astronomers say
Scientists say they detected the largest-ever merger of two black holes, forming one that is 225 times the mass of the sun, adding that the new discovery "pushes the limits of" how astronomers understand how black holes are created. Two black holes combined to make the massive one, according to the LIGO-Virgo-KAGRA Collaboration, an international group that uses gravitational waves to detect black hole mergers and who identified the event. Gravitational waves occur when there are minute distortions in spacetime, caused by events like black hole mergers, the group said in a news release. One of the black holes was about 103 times the mass of the sun. The other was about 137 times it. These large black holes may have been formed by even earlier mergers, Professor Mark Hannam, from Cardiff University and a member of the LIGO Scientific Collaboration, said in a news release. Even within the merger, the black holes are rapidly spinning, scientists said. Their rotation speed is about 400,000 Earth's rotation speed, the collaboration said in a graphic. They are moving at about 80% to 90% of the maximum possible speed. "The black holes appear to be spinning very rapidly — near the limit allowed by Einstein's theory of general relativity," said Dr. Charlie Hoy, a gravitational-wave astrophysicist, LIGO member and postdoctoral research fellow at the University of Portsmouth, in the news release. "That makes the signal difficult to model and interpret." The massive black hole has been dubbed GW231123. Its unusual size and behavior is challenging scientists' understanding of black hole formation, Hannam said. Previously, the largest known black hole that came from a merger was about 140 times the mass of the sun. GW231123's discovery is also opening doors for new avenues of research, astronomers said. The behavior and size of the black hole "pushes the limits of" current theoretical models and existing gravitational-wave detection technology, the LIGO-Virgo-KAGRA Collaboration said. "It will take years for the community to fully unravel this intricate signal pattern and all its implications," Dr. Gregorio Carullo, a LIGO member and an assistant professor at the University of Birmingham's Institute for Gravitational Wave Astronomy, said in a statement. "Despite the most likely explanation remaining a black hole merger, more complex scenarios could be the key to deciphering its unexpected features. Exciting times ahead!" The black hole was discovered in November 2023, during an observation period by the LIGO-Virgo-KAGRA Collaboration. The observation period began in May 2023, and the first part of the period ended in January 2024. More information about GW231123 and other black holes discovered by the collaboration will be presented this month at the 24th International Conference on General Relativity and Gravitation (GR24) and the 16th Edoardo Amaldi Conference on Gravitational Waves, two conferences presented jointly in Glasgow, Scotland. Data from the observation window will be published later in the summer. The data used to detect and study the massive black hole will also be made available for other researchers to use, the collaboration said.
