The True Scale of the Universe | Unveiled

The True Scale of the Universe

The universe is big, that much is certain. But it’s easy to lose perspective of the objects and distances at work when they reach a certain size because there’s really nothing to compare them to. And yet, for a long time now, humanity has been trying to in some way measure its reality. This is Unveiled, and today we’re answering the extraordinary question; What is the true scale of the universe? The first hurdle in measuring the universe is the measurements themselves. Determining the “size” of anything in outer space is difficult because there are so many metrics in play. You could measure the mass of something, the volume, the diameter… and each would give different results. Black holes, for example, are massive, but usually don’t have large diameters relative to that mass. The supermassive black hole at the centre of the Milky Way, Sagittarius A-star, has a diameter around 30-to-40 times that of our sun… which is big, but is also much smaller than some larger stars. Stars, by contrast, can have much less mass but still spread across a vast area, making them appear far larger. For this video, we’re primarily working from the diameters of celestial objects as the best metric to determine their size. Planet Earth is the largest of the four inner planets in our solar system, though its diameter is only around 400 miles more than Venus’s; which is sometimes called Earth’s evil twin. Mars and Mercury are both much smaller, with Mercury being only twice Pluto – keeping in mind that Pluto’s small size was one of the reasons that it was recategorized as a dwarf planet, in 2006. Mars is 4,212 miles across; more than 3,700 miles smaller than Earth. But the moon can actually hold its own here, being nearly 2,200 miles in diameter and therefore also larger than Pluto. But, bizarrely, just the area taken up by the Pacific Ocean on Earth is still wide enough that the entire moon could comfortably fit inside it. In terms of distances, the moon is obviously the closest thing to us, as well; but even it is 238,855 miles away. If the Earth were the size of a tennis ball, the moon would sit roughly seven feet away from it. The biggest planets in our solar system are the gas giants, and the biggest by far is Jupiter; which has a diameter of almost 87,000 miles, meaning Earth could fit inside it more than 1,300 times over. While the gas giants are huge, however, they also have very low densities; leading to the popular (though not exactly accurate) assertion that if you had a body of water vast enough to hold Saturn, it could float. Really, though, it’s not uncommon for gaseous planets to balloon to such incredible sizes – more interesting are exceptionally large rocky worlds. Leading candidates as the largest known planets of this type include Kepler 10c, discovered in 2011 with 17 times more mass than Earth, and the catchily named BD+20 594b, discovered in 2016 and thought to have a diameter more than double Earth’s. Places like these are so big that they’re officially classified as Mega-Earths. But planets certainly aren’t the biggest objects in the universe – not by a long shot. Stars are generally the largest singular objects. Our sun is by far the largest thing in the solar system, but it’s still not that big compared to others. The largest star we’ve ever found is UY Scuti, which boasts a diameter 1,700 times larger than the sun’s - despite being only 30 times more massive. The brightest star in our sky – apart from the sun, obviously – is Sirius, otherwise known as the “Dog Star”. The heaviest star is neither UY Scuti or Sirius, though; it’s a blue dwarf currently christened R136a1, which has 315 times the mass of the sun. But, let’s zoom out further. Galaxies, made up of billions and billions of stars and planets combined, are among the biggest structures in the universe. Our own, the Milky Way, is thought to be an average-sized galaxy with an estimated diameter of at least 100,000 lightyears. So far, we’ve only found a few thousand star systems in the Milky Way, but scientists predict that there could be billions more that we’ve yet to locate... and that’s just in our galaxy alone. Working mostly with data from the Hubble telescope, astronomers have estimated that there are between 100 and 200 billion galaxies in the observable universe. The smallest of those are thought to be just 3,000 lightyears across, while the largest are over 300,000 lightyears across. The closest “other” galaxy to us is Andromeda, which is over 2.5 million lightyears away. The really interesting part? In roughly 4.5 billion years, when the Earth is twice as old as it is now, Andromeda and the Milky Way are set to collide and blend into one giant galaxy - something which some scientists are already calling “Milkdromeda”. In reality, though, it’s unlikely that we will ever see these distant planets, stars or galaxies up close, simply because of the unfathomably huge distances between anything in outer space. Humans haven’t even been to another planet in the solar system yet, but the solar system is really quite small in the grand cosmic scheme of things – with a radius from the sun of around 1.87 lightyears, and a lightyear equating to around 5.88 trillion miles. That means it takes nearly two years for even light to travel out of just our star system. In general, though, the solar system is too small to practically measure it in lightyears; instead we use Astronomical Units, with one AU the equivalent to the average distance between the Earth and the sun – roughly 93 million miles. The distance from the sun to the outermost edge of the solar system is 100,000 AU, but the next closest star to us, Proxima Centauri, is more than double that distance at over 268,000 AU, or 4.2 lightyears, away. In 2015, the new Horizons probe reached Pluto after a journey of more than nine years... Say we continued at that speed, we’d reach Proxima Centauri in around 55,000 years’ time! At the highest estimates, modern humans have only been on Earth for 300,000 years… so we’d need one-sixth of the whole of human history to make just a one-way trip to just the closest star system to our own out of the billions of star systems in the entire universe! But, what’s even crazier is that all of these objects - the planets, moons, stars and galaxies - are only what we can see in the observable universe. The true universe is so huge that the light from the Big Bang hasn’t yet reached every corner of it, despite travelling for close to 14 billion years. According to a 2011 study conducted by a team at Oxford University, the universe could even be as much as 250 times bigger than what we can currently see… which puts it at seven trillion lightyears across! But because of cosmic expansion, if those 7 trillion lightyears were ever “observed”, by the time the light had reached that far the universe may have grown to be even bigger. And, finally, when you consider that only 5% of everything is all that we can see and comprehend - the rest being dark energy and dark matter - then the staggering entity we’re dealing with truly makes itself known. Space is larger than we can possibly comprehend, but it’s still getting bigger and bigger. And that’s the true scale of the universe.