Category: cosmology

Ask Ethan: Will Future Civilizations Miss The …

Ask Ethan: Will Future Civilizations Miss The Big Bang?

“If intelligent life re-emerges in our solar system in a few billion years, only a few points of light will still be visible in the sky. What kind of theory of the universe will those beings concoct? It is almost certain to be wrong. Why do we think that what we can view now can lead us to a “correct” theory when a few billion years before us, things might have looked completely different?”

Incredibly, the Universe we know and love today won’t be the way it is forever. If we were born in the far future, perhaps a hundred billion years from now, we wouldn’t have another galaxy to look at for a billion light years: hundreds of times more distant than the closest galaxies today. Our local group will merge into a single, giant elliptical galaxy, and there will be no sign at all of young stars, of star-forming regions, of other galaxies, or even of the Big Bang’s leftover glow. If we were born in the far future, we might miss the Big Bang as the correct origin of our Universe. It makes one wonder, when you think about it in those terms, if we’re missing something essential about our Universe today? In the 13.8 billion years that have passed, could we already have lost some essential information about the history of our Universe?

And in the far future, might we see something that, as of right now, hasn’t yet grown to prominence? Let’s explore this and see what you think!

Astronomers Confirm Second Most-Distant Galaxy…

Astronomers Confirm Second Most-Distant Galaxy Ever, And Its Stars Are Already Old

“Scientists have just confirmed the second most distant galaxy of all: MACS1149-JD1, whose light comes from when the Universe was 530 million years old: less than 4% of its present age. But what’s remarkable is that we’ve been able to detect oxygen in there, marking the first time we’ve seen this heavy element so far back. From the observations we’ve made, we can conclude this galaxy is at least 250 million years old, pushing the direct evidence for the first stars back further than ever.”

When it comes to the most distant galaxies of all, our current set of cutting-edge telescopes simply won’t get us there. The end of the cosmic dark ages and the dawn of the first cosmic starlight is a mystery that will remain until at least 2020: when the James Webb Space Telescope launches. Using the power of a multitude of observatories, we’ve managed to find a gravitationally lensed galaxy whose light comes to us from over 13 billion years ago. But unlike previous galaxies discovered near that distance, we’ve detected oxygen in this one, allowing us to get a precise measurement and to estimate its age.

For the first time, we have evidence from galaxies, directly, that the Universe’s first stars formed no later than 250 million years after the Big Bang. Here’s how we know.

Aliens In The Multiverse? Here’s Why Dar…

Aliens In The Multiverse? Here’s Why Dark Energy Doesn’t Tell You Anything

“It’s important to recognize that there are a wide variety of possible values that dark energy could have, including significantly larger values, that would still lead to a Universe very much like our own. Until we understand where these values come from, and what makes one set of values more likely than another, it’s grossly unfair to claim that we won the cosmic lottery in having a Universe with the values ours possesses. Unless you know the rules that govern the game you’re playing, you have no idea how likely or unlikely the one result you see actually was.”

There are a series of interesting results that have just emerged from the EAGLE collaboration, which has been simulating the Universe to learn what types of stars and galaxies form within it. They varied the value of dark energy in it tremendously, and found that even if you increased the amount by five, ten, or fifty times as much, you’d still form plenty of stars and galaxies: enough to give you chances at life like we have here. This surprised them, since they assumed the value of dark energy we have is finely-tuned to allow life. But it appears that things may not be as finely-tuned as we had thought! The simulation results are interesting, but this doesn’t really tell you anything about aliens in the Multiverse, since we have no idea what causes dark energy to have the values that it does.

Until we know the rules that govern this, we can’t really say what dark energy tells us about aliens in Universes other than our own. Here’s why.

How Does Our Earliest Picture Of The Universe …

How Does Our Earliest Picture Of The Universe Show Us Dark Matter?

“So all you need to do, to know whether your Universe has dark matter or not, is to measure these temperature fluctuations that appear in the CMB! The relative heights, locations, and numbers of the peaks that you see are caused by the relative abundances of dark matter, normal matter, and dark energy, as well as the expansion rate of the Universe. Quite importantly, if there is no dark matter, you only see half as many total peaks! When we compare the theoretical models with the observations, there’s an extremely compelling match to a Universe with dark matter, effectively ruling out a Universe without it.”

If your young Universe is full of matter and radiation, what happens? Gravitation works to pull matter into the overdense regions, but that means that the radiation pressure must rise in those regions, too, and that pushes back against the matter. On small scales, this pushback washes out the gravitational growth, but on large-enough scales, the finite speed that light can travel means that no wash-out can happen. Dark matter, however, doesn’t collide with radiation or normal matter, while normal matter collides with both radiation and itself. If we can calculate exactly how these three species interplay, we can calculate what types of patterns we expect to see in the Big Bang’s leftover glow, and then compare it with what we observe with satellites like WMAP and Planck. And what have we seen, exactly, when we’ve done that? 

We see that the Universe must contain dark matter to explain the observations. No alternative theory can match it.

When Will We Break The Record For Most Distant…

When Will We Break The Record For Most Distant Galaxy Ever Discovered?

“Finally, beyond a certain distance, the Universe hasn’t formed enough stars to reionize space and make it 100% transparent.

We only perceive galaxies in a few serendipitous directions, where copious star-formation occurred.
In 2016, we fortuitously discovered GN-z11 at a redshift of 11.1: from 13.4 billion years ago.
But recent, indirect evidence suggests stars formed at even greater redshifts and earlier times.“

It was only a couple of years ago that we set the current record for where the most distant galaxy is: from 13.4 billion years ago, when the Universe was just 3% its current age. This record is unlikely to be broken with our current set of observatories, as discovering a galaxy this distant required a whole bunch of unlikely, serendipitous phenomena to line up at once. But in 2020, the James Webb Space Telescope will launch: an observatory optimized for finding exactly the kinds of galaxy that push past the limits of what Hubble can do. We fully expect to not only break the record for most distant galaxy ever discovered, but to learn, for the first time, exactly where and when the first galaxies in the Universe truly formed.

Until then, it’s lots of fun to speculate as to when and where they might be, but it will take the observations of a lifetime to smash this cosmic record!

Ask Ethan: How Big Will The Universe Get? “Th…

Ask Ethan: How Big Will The Universe Get?

“The current estimate for the diameter of the universe is 93 billion light years. With the current acceleration of the universe measured by redshift, and the future exponential acceleration, how long until “we” hit a diameter of 100 billion light years?”

Our Universe is made up of a number of different types of energy, including dark energy, dark matter, normal matter, neutrinos, and radiation. When you combine those different forms of energy with our observed expansion rate, you arrive at a Universe prediction for how the Universe expanded in the past and how it will continue to expand into the future. As distant galaxies accelerate away from us, we can make predictions for how large our observable Universe will get as time goes on. At present, our visible Universe is 92 billion light years in diameter, with an age of 13.8 billion years. When will we hit 100 billion light years? Or a trillion? Or a quadrillion?

The answer is straightforward, fun, and profound. Come find out how big the Universe will get, and how fast it will get there, on this week’s Ask Ethan!

Hubble’s Greatest Discoveries Weren&rsqu…

Hubble’s Greatest Discoveries Weren’t Planned; They Were Surprises

“And if we head out beyond our own galaxy, that’s where Hubble truly shines, having taught us more about the Universe than we ever imagined was out there. One of the greatest, most ambitious projects ever undertaken came in the mid-1990s, when astronomers in charge of Hubble redefined staring into the unknown. It was possibly the bravest thing ever done with the Hubble Space Telescope: to find a patch of sky with absolutely nothing in it — no bright stars, no nebulae, and no known galaxies — and observe it. Not just for a few minutes, or an hour, or even for a day. But orbit-after-orbit, for a huge amount of time, staring off into the nothingness of empty space, recording image after image of pure darkness.

What came back was amazing. Beyond what we could see, there were thousands upon thousand of galaxies out there in the abyss of space, in a tiny region of sky.”

28 years ago today, the Hubble Space Telescope was deployed. Since that time, it’s changed our view of the Solar System, the stars, nebulae, galaxies, and the entire Universe. But here’s the kicker: almost all of what it discovered wasn’t what it was designed to look for. We were able to learn so much from Hubble because it broke through the next frontier, looking at the Universe in a way we’ve never looked at it before. Astronomers and astrophysicists found clever ways to exploit its capabilities, and the observatory itself was overbuilt to the point where, 28 years later, it’s still one of the most sought-after telescopes as far as observing time goes.

Hubble’s greatest discoveries weren’t planned, but the planning we did enabled them to become real. Here are some great reasons to celebrate its anniversary.

The Most Important Equation In The Universe &…

The Most Important Equation In The Universe

“The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it’s headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!”

In 1915, Einstein put forth General Relativity as a new theory of gravity. It reproduced all of Newton’s earlier successes, solved the problem that Newton couldn’t of Mercury’s orbit, and made a new prediction of bent starlight by large masses, verified during the 1919 solar eclipse. Despite the fact that it included a cosmological constant to keep the Universe static, that didn’t deter Soviet physicist Alexander Friedmann from solving Einstein’s equations for a Universe that was filled with matter and energy, all the way back in 1922. The two generic equations he found, known as the Friedmann equations, immediately related measurable quantities like the amount of matter in the Universe to the expansion or contraction rate, which just years later became validated by Hubble’s observations. But the young Friedmann never lived to see it; he died of typhoid fever contracted when he was returning from his honeymoon in 1925.

Nearly 100 years later, it still stands as the equation that determines the history and fate of the Universe. Come see why I call it the most important equation in the Universe!

Ask Ethan: How Will Our Universe End? “When w…

Ask Ethan: How Will Our Universe End?

“When will our universe reach the point of maximum entropy? And what other possibilities exist for our universe in the far future?”

It’s nearly 14 billion years since the hot Big Bang gave rise to our observable Universe, which now consists of some 2 trillion galaxies spread out across a sphere over 46 billion light years in radius. But despite how plentiful the matter in our Universe is, it won’t last forever. The stars will all burn out, and even the new stars that form will eventually run out of gas to form from. Dark energy will drive the unbound galaxies away, while gravitation will pull the bound ones into a single structure. Over time, ejections and mergers occur, littering the Universe with isolated masses and setting up enormous black holes embedded in dark matter halos as the last remnants of galaxies. After enough time passes, the final black holes decay, leaving only low-energy, ultra-high-entropy radiation behind.

It will take a long time, but this is the ultimate fate of everything in the far future of the Universe!

What Astronomers Wish Everyone Knew About Dark…

What Astronomers Wish Everyone Knew About Dark Matter And Dark Energy

“It wasn’t always apparent that this would be the solution, but this one solution works for literally all the observations. When someone puts forth the hypothesis that “dark matter and/or dark energy doesn’t exist,” the onus is on them to answer the implicit question, “okay, then what replaces General Relativity as your theory of gravity to explain the entire Universe?” As gravitational wave astronomy has further confirmed Einstein’s greatest theory even more spectacularly, even many of the fringe alternatives to General Relativity have fallen away. The way it stands now, there are no theories that exist that successfully do away with dark matter and dark energy and still explain everything that we see. Until there are, there are no real alternatives to the modern picture that deserve to be taken seriously.”

If you yourself are not a professional astronomer or astrophysicist, you might feel in your gut that dark matter and dark energy just can’t be right. How could we possibly conclude that only 5% of our Universe is made out of the matter that everything we know of is composed of, and that 95% of the Universe is made of some dark substance we’ve never successfully detected. It sounds crazy, and therefore, you wonder, isn’t there some simpler explanation that’s likely correct? It’s not just you: the professionals have wondered this, too. And if there is, it means we have to throw out all of the successes we’ve achieved so far. So goodbye, General Relativity. Goodbye to the Big Bang, to astrophysics, to structure formation, to what we know about stars and galaxies, to gravitational lensing, to gravitational waves, and so much more. To get rid of dark matter and dark energy, we have to throw out the baby with the bathwater.

There are countless lines of evidence that support the dark matter and dark energy picture, and astronomers wish the public (and some of their contrarian colleagues) knew about this. Now, you can know for yourself.