No, The Universe Cannot Be A Billion Years Younger Than We Think
“There may be some who contend we don’t know what the age of the Universe is, and that this conundrum over the expanding Universe could result in a Universe much younger than what we have today. But that would invalidate a large amount of robust data we already have and accept; a far more likely resolution is that the dark matter and dark energy densities are different than we previously suspected.
Something interesting is surely going on with the Universe to provide us with such a fantastic discrepancy. Why does the Universe seem to care which technique we use to measure the expansion rate? Is dark energy or some other cosmic property changing over time? Is there a new field or force? Does gravity behave differently on cosmic scales than expected? More and better data will help us find out, but a significantly younger Universe is unlikely to be the answer.”
There’s a fascinating conundrum facing modern cosmology today. If you measure the distant light from the Universe, from the cosmic microwave background or from how the large-scale structure within it has evolved, you can get a value for the expansion rate of the Universe: 67 km/s/Mpc. On the other hand, you can also get a measurement for that rate from measuring individual objects through a technique known as the cosmic distance ladder, and you get a value of 73 km/s/Mpc. These two values differ by 9%, and are inconsistent with one another. Recently, one of the groups studying this puzzle claimed that the Universe might be 9% younger than currently expected: 12.5 billion years old instead of 13.8 billion years old.
“During the red giant phase, Mercury and Venus will certainly be engulfed by the Sun, while Earth may or may not, depending on certain processes that have yet to be fully worked out. The icy worlds beyond Neptune will likely melt and sublimate, and are unlikely to survive the death of our star.
Once the Sun’s outer layers are returned to the interstellar medium, all that remains will be a few charred corpses of worlds orbiting the white dwarf remnant of our Sun. The core, largely composed of carbon and oxygen, will total about 50% the mass of our present Sun, but will only be approximately the physical size of Earth.”
Looking forward in time, the death of our Sun is easy to envision, as we’ve seen Sun-like stars in their dying phases and immediately afterwards plenty of times. But what happens after that, in the far future? Will our Sun’s corpse remain a white dwarf forever? Will it simply cool down, radiating heat away? Or will something exciting happen?
Maybe we’ll get ejected from the galaxy. Maybe we’ll get devoured by a black hole. Maybe we’ll merge with another object, or experience an interaction that forever changes us from what we were. Maybe we’ll even experience a cataclysm that destroys our stellar corpse entirely!
“Recently, a new black hole, J1342+0928, was discovered to originate from 13.1 billion years ago: when the Universe was 690 million years old, just 5% of its current age. It has a mass of 800 million Suns, an exceedingly high figure for such early times. Even if black holes formed from the very first stars, they’d have to accrete matter and grow at the maximum rate possible — the Eddington limit — to reach this size so rapidly. Fortunately, other methods may also grow a supermassive black hole.”
One of the puzzles of how our Universe grew up is how the supermassive black holes we find at the centers of galaxies got so big so fast. We’ve got multiple black holes that come from when the Universe was less than 10% of its current age that are already many hundreds of millions, if not billions, of solar masses in size. How did they get so big so fast? While many hypothesize exotic scenarios like our Universe being born with (primordial) black holes, there is no evidence for such an extraordinary leap. Could conventional astrophysics, and the realistic conditions of our early Universe, actually lead to black holes so massive so early on?
Ask Ethan: What’s The Real Story Behind This Dark Matter-Free Galaxy?
“I read a study that said the mystery of a galaxy with no dark matter has been solved. But I thought that this anomalous galaxy was previously touted as evidence FOR dark matter? What’s really going on here, Ethan?”
Imagine you looked at the Universe, and saw a galaxy unlike any other. Whereas every other galaxy we’ve ever looked at exhibited a large discrepancy between the amount of matter that’s present in stars and the total amount of gravitational mass we’d infer, this new galaxy appears to have no dark matter at all. What would you do? If you’re being a responsible scientist, you’d try to knock down this galaxy by any scrupulous means possible. You’d wonder if you had mis-estimated one of its properties. You’d try to re-confirm the measurements with different instruments and techniques. And you’d wonder if there weren’t an alternative explanation for what we were seeing.
“Even though we can trace our cosmic history all the way back to the earliest stages of the hot Big Bang, that isn’t enough to answer the question of how (or if) time began. Going even earlier, to the end-stages of cosmic inflation, we can learn how the Big Bang was set up and began, but we have no observable information about what occurred prior to that. The final fraction-of-a-second of inflation is where our knowledge ends.
Thousands of years after we laid out the three major possibilities for how time began — as having always existed, as having begun a finite duration ago in the past, or as being a cyclical entity — we are no closer to a definitive answer. Whether time is finite, infinite, or cyclical is not a question that we have enough information within our observable Universe to answer. Unless we figure out a new way to gain information about this deep, existential question, the answer may forever be beyond the limits of what is knowable.”
If you didn’t know anything about the Universe, you might intuit three possibilities for how time originated. Either it had a beginning a finite duration ago, or it existed for an eternity into the past, or it is cyclical in nature, with no beginning, end, or true delineation between past and future. But we have lots of physical evidence today. We know about the Big Bang and what its limits are. We know about cosmic inflation, which preceded and set up the Big Bang. And we know about dark energy, which determines the fate of our Universe.
Scientists Discover Space’s Largest Intergalactic Bridge, Solving A Huge Dark Matter Puzzle
“Lo and behold, these shocks are some of the first things you notice if you look at the Chandra images of the Bullet cluster on their own! The fact that we’ve identified relativistic charged particles in the presence of a large-scale magnetic field in one pair of colliding clusters is strongly suggestive of the same effects existing in other clusters. If this same type of structure that exists between Abell 0399 and Abell 0401 also exists between other colliding clusters, it could solve this minor anomaly of the Bullet cluster, leaving dark matter as the sole unchallenged explanation for the displacement of gravitational effects from the presence of normal matter.
It’s always an enormous step forward when we can identify a new phenomenon. But by combining theory, simulations, and the observations of other colliding galaxy clusters, we can push the needle forward when it comes to understanding our Universe as a whole. It’s another spectacular victory for dark matter, and another mystery of the Universe that might finally be solved by modern astrophysics. What a time to be alive.”
When two galaxy clusters collide, the normal matter heats up and emits X-rays, experiencing shocks and separating from the gravitational effects of the clusters they originated from. But as compelling as this evidence is for dark matter, a few of the colliding clusters we’ve found, such as the original (the Bullet cluster), appear to be moving faster than theory predicts. Either dark matter is incomplete, our observations were wrong, or something else is working besides gravity to accelerate the matter.
“Upon observing it, Charles Messier wrote: “it is very dull, but perfectly outlined; it is as large as Jupiter & resembles a planet which is fading.” This observation originated the misnomer “planetary nebula,” but physically originates when dying stars expel their outer layers. Despite looking very much like a ring to our eyes, the Ring Nebula is anything but.”
There are few objects in the night sky as famous or striking as the Ring Nebula. Discovered way back in 1779, its visual, ring-like shape can easily be seen with the human eye through even a modest telescope. But despite its appearances, it’s no ring at all. There’s a large, diffuse outer halo, a series of intricate, extended, knotty hydrogen structures, two lobes that extend even larger than the ring component but along our line-of-sight, and finally that bright, high-density donut that appears ring-like to our eyes. At just over 2,000 light years away, it is the closest planetary nebula to Earth, and the template for what we think will happen to our Solar System when the Sun dies.
Ask Ethan: What’s It Like When You Fall Into A Black Hole?
“[W]hat is it like to be/fall inside a rotating black hole? This is not observable, but calculable… I have talked with various people who have done these calculations, but I am getting old and keep forgetting things.”
I get a lot of questions that people submit for Ask Ethan, but only rarely do they come to me from other scientists who tower above me in the field. This week’s question, from Event Horizon Telescope scientist extraordinaire Heino Falcke, asks me to help him visualize what it would look like if you fell into a black hole. Not just any black hole, mind you, but a realistic, rotating black hole. There’s really only one person on Earth who understands this well enough: Andrew Hamilton, who has devoted the last 15 years of his life to figuring out what it looks like and what it means when this actually happens.
When Will The Universe Get Its First ‘Black Dwarf’ Star?
“We currently conceive of our Universe as littered with stars, which cluster together into galaxies, which are separated by vast distances. But by time the first black dwarf comes to be, our local group will have merged into a single galaxy (Milkdromeda), most of the stars that will ever live will have long since burned out, with the surviving ones being exclusively the lowest-mass, reddest and dimmest stars of all. And beyond that? Only darkness, as dark energy will have long since pushed away all the other galaxies, making them unreachable and practically unmeasurable by any physical means.
And yet, amidst it all, a new type of object will come to be for the very first time. Even though we’ll never see or experience one, we know enough of nature to know not only that they’ll exist, but how and when they’ll come to be. And that, in itself — the ability to predict the far-distant future that has not yet come to pass — is one of the most amazing parts of science of all!”
When stars like our Sun die, the remnants may be smaller and fainter and lower in mass, but they’re still extremely hot: hot enough to shine and emit light. They cool, though, as they no longer undergo nuclear fusion. At some point in the far distant future, they’ll have radiated enough of their energy away that they’ll finally go dark, creating a hypothetical star known as a black dwarf.