Category: cosmology

This Is How Astronomers Know The Age Of The Universe (And You Can, Too)

“The reason that we can claim the Universe is 13.8 billion years old to such enormous precision is driven by the full suite of data that we have. A Universe that expands more quickly needs to have less matter and more dark energy, and its Hubble constant multiplied by the age of the Universe will have a larger value. A slower-expanding Universe requires more matter and less dark energy, and its Hubble constant multiplied by the age of the Universe gets a smaller value.

However, in order to be consistent with what we observe, the Universe can be no younger than 13.6 billion years and no older than 14.0 billion years, to more than 95% confidence. There are many properties of the Universe that are indeed in doubt, but its age isn’t one of them. Just make sure you take the Universe’s composition into account, or you’ll wind up with a naive — and incorrect — answer.”

Earlier this year, there was a report that the Universe could have been a billion years younger than we currently think. Many people still think that you can calculate the age of the Universe directly from the Hubble constant. And even though the concept of the age of the Universe is a simple one to understand, the pitfalls are so numerous that even Nobel Laureates can fall into them.

We know the age of the Universe to a remarkable and unambiguous precision: 13.8 billion years. Here’s how we get there and how you can get there yourself, too.

Ask Ethan: Do Ancient Galaxies Get Magnified By The Expanding Universe?

“Do ancient galaxies appear larger to us than they really were, due to the expansion of the Universe? If so, then by how much?”

It seems like the simplest, most straightforward idea in the world: the farther away an object is, the smaller it appears. View the same object when it’s twice as far away, and it will only appear to be half as large in terms of angular size. Place it ten times as far away, and you’ll see it appear just one-tenth the size. 

But this is only true in flat, static space. In the expanding Universe, this relationship falls apart, particularly when you factor in dark energy. More distant objects appear smaller the farther away you look, but only to a point. Galaxies that are about 14-to-15 billion light-years away will appear the smallest, and then the same-sized galaxy will actually appear larger the farther away you look! This may be counterintuitive, but there’s real, solid science to back it up. 

Come learn how the expanding Universe really does magnify the most distant galaxies of all, and what the fascinating implications are for the next generation of ultra-powerful telescopes!

Ask Ethan: Was The Critical Evidence For The Big Bang Discovered By Accident?

“The cosmic microwave background is a landmark evidence of the Big Bang origin of the universe. How come this discovery is labelled as an accidental one?”

Imagine that you lived in a world where nobody knew where the Universe came from. Sure, different theories led to a myriad of possibilities, but it takes observations to decide what’s correct in this Universe. In the 1920s, Georges Lemaitre worked out the first early details of the Universe originating from a hot, dense state. In the 1940s, George Gamow and his collaborators started to pull out robust predictions, like the nuclear predictions for fusion in the early Universe, the growth of stars, galaxies and clusters in the Universe, and the existence and rudimentary properties of a leftover glow: today’s Cosmic Microwave Background. Yet the actual discovery of this leftover radiation from the Big Bang, despite the meticulous planning of a group working to detect it explicitly, truly was a serendipitous accident. 

You’ll never look at the expression “one astronomer’s noise is another astronomer’s data” the same way again!

Ask Ethan: Could The Shape Of Our Universe Be Closed Instead Of Flat?

“I thought that the curvature parameter had been essentially settled upon by WMAP, Planck, and other astronomical measurements. I am curious what you think about the validity of this recent paper. Is the Universe actually closed with a detectable positive curvature as the authors of the Nature Astronomy paper suggest? If the Universe is spherical, then how big would the sphere be according their measurements?”

About 2 weeks ago, a team of scientists took a detailed look at the latest Planck results, the most sophisticated, highest-precision map of the Cosmic Microwave Background ever obtained. But rather than look simply at the temperature fluctuations, they looked at a different signal: the effect of gravitational lensing. And instead of finding the flat Universe that other types of analysis yield, they favored a closed, positively-curved Universe at about the 4.4% level, creating a greater-than-3-sigma tension with the rest of the Planck data.

Does that mean the Universe could be closed instead of flat? Not if you look at the consequences of this dastardly interpretation. Get the real science on Ask Ethan today.

This Is How Astronomers Will Finally Measure The Universe’s Expansion Directly

“This is why, by measuring the redshifts and distances to a slew of objects ⁠— objects at a variety of different distances and redshifts ⁠— we can reconstruct the expansion of the Universe over its history. The fact that a whole slew of disparate data sets are all consistent with not only one another but with an expanding, evenly filled Universe in the context of relativity, that gives us the confidence we have in our model of the Universe.

But, just as we didn’t necessarily accept gravitational waves before they were directly measured by LIGO, there’s still the possibility that we’ve made a mistake somewhere in inferring the properties of the Universe. If we could take a distant object, measure its redshift and distance, and then come back at a later time to see how its redshift and distance had changed, we’d be able to directly (instead of indirectly) measure the expanding Universe for the first time.”

We’ve measured the distance to literally billions of objects all over the Universe, from within our galaxy to more than 30 billion light-years away. By observing how the light from these distant objects is shifted, we’re able to infer that the Universe is expanding. We’re able to infer how that expansion rate has changed over time. And we’re able to infer what the Universe is made of: a monumental accomplishment.

But what we’ve never been able to do, as of 2019, is to watch an individual, distant galaxy physically expand away from us in real-time. With the new generation of 30-meter class telescopes we have coming online, though, all of that is poised to change. When the ELT arrives, the largest of the next generation telescopes at 39 meters, it will have the capability to make this measurement directly by observing the same sets of quasars 10 years apart.

You’re going to get to learn a new term today: redshift drift. When we measure it, we’ll have our first direct observation of the Universe as it physically expands on human timescales.

This Is How Distant Galaxies Recede Away From Us At Faster-Than-Light Speeds

“All the galaxies in the Universe beyond a certain distance appear to recede from us at speeds faster than light. Even if we emitted a photon today, at the speed of light, it will never reach any galaxies beyond that specific distance. It means any events that occur today in those galaxies will not ever be observable by us. However, it’s not because the galaxies themselves move faster than light, but rather because the fabric of space itself is expanding.

In the 7 minutes it took you to read this article, the Universe has expanded sufficiently so that another 15,000,000 stars have crossed that critical distance threshold, becoming forever unreachable. They only appear to move faster than light if we insist on a purely special relativistic explanation of redshift, a foolish path to take in an era where general relativity is well-confirmed. But it leads to an even more uncomfortable conclusion: of the 2 trillion galaxies contained within our observable Universe, only 3% of them are presently reachable, even at the speed of light.

If we care to explore the maximum amount of Universe possible, we cannot afford to delay. With each passing moment, another chance for encountering intelligent life forever slips beyond our grasp.”

If you look at a galaxy, chances are you’ll see that it appears to be receding away from us, as its light is redshifted. The more distant you look, the greater the redshift, and hence, the faster the implied recession speed. But this interpretation runs into problems very quickly: by the time you’re looking at galaxies more than 13-to-15 billion light-years away, they start to appear as though they’re receding faster than the speed of light!

Impossible, you say? Sure, if you only consider special relativity. If you insist on general relativity, it all falls into place. Here’s how.

This Is Why Einstein’s Greatest Blunder Really Was A Tremendous Mistake

“But there’s no retconning history; Einstein wasn’t right after all. While our Universe might actually have a non-zero cosmological constant, it isn’t there to stabilize our Universe. Rather, our Universe isn’t stable at all; it’s expanding from an initially hot, dense, and uniform state into the cold, sparse, and galaxy-rich cosmos we see today.

Einstein missed all of that because he insisted on a static Universe, and invented the cosmological constant to achieve that goal. Take it away, and you get a Universe that’s very much like the one we have today. The cosmological constant that affects our Universe serves to break the balance between the expansion and the other forms of matter-and-energy; it causes distant galaxies to accelerate away from us, pushing the Universe apart. Had Einstein predicted that, it would have been mind-boggling. Instead, he forced the equations to fit his (incorrect) assumptions, and missed the expanding Universe.”

When Einstein first set forth his General theory of Relativity, it included a term that no one had ever heard of before: a cosmological constant. Einstein had realized that a static Universe, the one he thought he lived in, was unstable. Gravitation would cause matter to collapse, and so something had to counteract that. His solution was to concoct a cosmological constant, something that he called his “greatest blunder” after the expanding Universe was confirmed.

Does the late-1990s discovery of dark energy, which might be a cosmological constant after all, mean that Einstein was actually right? Not at all. Come find out why today.

Astronomically Rare ‘Double Lens’ Yields Best Single System Measurement Of Cosmic Expansion

“Methods based on early signals imprinted in the cosmic microwave background and on the Universe’s large-scale structure indicate one value: 67 km/s/Mpc. However, methods relying on precise measurements to distant objects deliver a conflicting value: 74 km/s/Mpc. With overall errors of just 1-2% apiece, this 9% difference is significant and robust. Each new measurement has the opportunity to either validate or refute this growing tension.”

How quickly is the Universe expanding? You might think that’s a simple question, and it would be if every way we had of measuring that rate gave the same consistent answer. Only, what we’re finding is something very strange: measuring the expansion rate using an early-time signal gives one value, and measuring it using a late-time signal gives a different, inconsistent value.

The next step is to come up with as many different methods as possible of measuring this rate, and to see if the discrepancy persists. In a novel 2017 find, the system DES J0408-5354 was discovered, appearing to be a background objects lensed four times by a foreground galaxy. As it turns out, though, this is actually a double lens: two independent background sources lensed by the same foreground source, with each one creating multiple images.

This is an unprecedented system for measuring the expansion rate, and yields a value with just 3.9% uncertainty. Which group did it agree with? Come find out as the mystery deepens today!

What Came First: Inflation Or The Big Bang?

“In fact, our entire observable Universe contains no signatures at all from almost all of its pre-hot-Big-Bang history; only the final 10^-32 seconds (or so) of inflation even leave observably imprinted signatures on our Universe. We do not know where the inflationary state came from, however. It might arise from a pre-existing state that does have a singularity, it might have existed in its inflationary form forever, or the Universe itself might even be cyclical in nature.

There are a lot of people who mean “the initial singularity” when they say “the Big Bang,” and to those people, I say it’s long past due for you to get with the times. The hot Big Bang cannot be extrapolated back to a singularity, but only to the end of an inflationary state that preceded it. We cannot state with any confidence, because there are no signatures of it even in principle, what preceded the very end-stages of inflation. Was there a singularity? Maybe, but even if so, it doesn’t have anything to do with the Big Bang.”

Have you heard that our Universe began some 13.8 billion years ago with the start of the Big Bang? There’s a good chance that some version of that story has made it to you, but it unfortunately has probably gotten to you the same way it got to me: with an error that’s many decades out of date. 

What if I told you that you couldn’t extrapolate the Universe back to a singularity, where all the matter and energy was consolidated into a space so tiny that the laws of physics break down?

What if I told you that we have a verified, validated theory of what happened before the Big Bang, and it has (for decades, now) superseded and replaced the idea of an initial singularity as the earliest stages of the Universe?

Meet cosmic inflation, the pre-origin of our Universe that set up and gave rise to the Big Bang, and learn why the naysayers are out of legs to stand on.

Controversial ‘Dark Matter Free Galaxy’ Passes Its Most Difficult Test

“In theory, all galaxies should contain copious amounts of dark matter, with one exception. Galactic mergers, interactions, or gas stripping events can isolate large amounts of normal matter. These liberated clumps should gravitate and recollapse, creating dark matter-free galaxies. Detractors argued their absence proved dark matter’s non-existence. However, 2018 and 2019 saw scientists announce two dark matter-free galaxies: NGC 1052-DF2 and NGC 1052-DF4.”

One of the most counterintuitive predictions of dark matter is that, owing to the differing forces that normal matter and dark matter experience in environments rich in matter and radiation, it should be separable from normal matter. Therefore, when major galaxy mergers or interactions occur, it should be possible to strip normal matter out of the dark matter halos they’re bound to, creating dark matter-free galaxies.

Long predicted by theory but never discovered, they were used by dark matter detractors to demonstrate the insufficiency of dark matter. But in 2018, the galaxy NGC 1052-DF2 was measured well enough to conclude it was devoid of dark matter; in 2019, it was joined by NGC 1052-DF4. While a different team claimed these galaxies were closer and therefore not dark matter-free, the original researchers turned to Hubble to settle the matter.

NGC 1052-DF4 has now been measured better than ever before, and it’s at the original (farther) distance, implying that it really is dark matter-free. Come get the full story today.