Ask Ethan: How Large Is The Entire, Unobservable Universe?
“We know the size of the Observable Universe since we know the age of the Universe (at least since the phase change) and we know that light radiates. […] My question is, I guess, why doesn’t the math involved in making the CMB and other predictions, in effect, tell us the size of the Universe? We know how hot it was and how cool it is now. Does scale not affect these calculations?”
Our Universe today, to the best of our knowledge, has endured for 13.8 billion years since the Big Bang. But we can see farther than 13.8 billion light years, all because the Universe is expanding. Based the matter and energy present within it, we can determine that the observable Universe is 46.1 billion light years in radius from our perspective, a phenomenal accomplishment of modern science. But what about the unobservable part? What about the parts of the Universe that go beyond where we can see? Can we say anything sensible about how large that is?
We can, but only if we make certain assumptions. Come find out what we know (and think) past the limits of what we can see on this week’s Ask Ethan!
What Was It Like When The Big Bang First Began?
“Once inflation comes to an end, and all the energy that was inherent to space itself gets converted into particles, antiparticles, photons, etc., all the Universe can do is expand and cool. Everything smashes into one another, sometimes creating new particle/antiparticle pairs, sometimes annihilating pairs back into photons or other particles, but always dropping in energy as the Universe expands.
The Universe never reaches infinitely high temperatures or densities, but still attains energies that are perhaps a trillion times greater than anything the LHC can ever produce. The tiny seed overdensities and underdensities will eventually grow into the cosmic web of stars and galaxies that exist today. 13.8 billion years ago, the Universe as-we-know-it had its beginning. The rest is our cosmic history.”
The Big Bang is normally treated as the very beginning of the Universe, but in reality there’s a phase that came before the hot Big Bang to set it up. During cosmic inflation, the Universe was filled with an extremely large amount of energy inherent to space itself, causing the Universe to inflate, stretch flat, and achieve almost exactly the same properties everywhere. The Universe we have today, however, is full of matter and radiation, and originated in a hot Big Bang 13.8 billion years ago. How did we go from this inflating state to our hot, dense, uniform and expanding-and-cooling Universe?
This tells you the best scientific story of how we got there, along with an in-depth description of what it was like at those first moments where our Universe gave us something to look at.
The 7 Most Powerful Fireworks Shows In The Universe
“Forget mere chemical reactions; in space, matter-energy conversion creates unprecedentedly powerful explosive events.
Here are the 7 most powerful natural displays of cosmic fireworks.
7.) Type Ia supernova: when two white dwarf stars collide, they initiate a runaway fusion reaction, destroying both stellar remnants.”
Throughout the Universe, there are many beautiful displays of cosmic fireworks. Stars are born; galaxies collide; gas gets heated and expelled; stars and stellar remnants explode and die. We typically think of supernova events as the culmination of the brightest, most energetic things that can happen in the cosmos. But supernovae only fill up the bottom rungs on the list of the most powerful, natural fireworks shows that the Universe provides us with.
Which ones are the most energetic? Find out on this incredible start to your pre-4th-of-July Monday!
Ask Ethan: Could The Universe Be Torn Apart In A Big Rip?
“Is The Big Rip—where expansion exceeds all the other forces—still considered a possible future for our Universe? What are the arguments for or against? And if so, how would it unfold, what would happen?”
In addition to normal matter, dark matter, neutrinos, and radiation, the Universe is made up of dark energy: a new form of energy intrinsic to space itself. Although the data indicates that dark energy is consistent with being a cosmological constant, whose energy density won’t change with time, it’s possible that this energy will increase or decrease in strength. If it decreases, it could decay entirely or even reverse sign. resulting in a Big Crunch. But if it increases, we could have a spectacularly catastrophic fate: the Big Rip. In the Big Rip, bound objects will literally be ripped apart on galactic, stellar, planetary, and eventually even atomic scales. Even space itself will rip apart in the end.
The Big Rip isn’t ruled out, but if it’s going to occur, our current constraints push it out to 80 billion years in the future. Find out what it would look like and how we’ll know!
What Was It Like When The Universe Was Inflating?
“In theory, what lies beyond the observable Universe will forever remain unobservable to us, but there are very likely large regions of space that are still inflating even today. Once your Universe begins inflating, it’s very difficult to get it to stop everywhere. For every location where it comes to an end, there’s a new, equal-or-larger-sized location getting created as the inflating regions continue to grow. Even though most regions will see inflation end after just a tiny fraction of a second, there’s enough new space getting created that inflation should be eternal to the future.”
You’ve no doubt heard that the overwhelming scientific consensus is that the observable Universe began with the hot Big Bang. What’s far less common, but just as overwhelmingly accepted and well-understood, is that a period of cosmological inflation occurred prior to the Big Bang in order to set it up. While most of us can visualize the expanding Universe fairly well, it’s much more difficult to get a good handle on what the Universe looked like during the epoch of cosmic inflation. Yet if you want to know where our Universe came from, and how it was born with the properties our hot Big Bang started off with, that’s exactly the challenge you have to meet.
Here’s an in-depth but scientifically accurate description of what the Universe was like when inflation occurred, and how it gives us the Universe we inhabit today!
We Just Found The Missing Matter In The Universe, And Still Need Dark Matter
“For over 40 years, scientists have argued over dark matter’s existence.
Big questions arose from the motions inside galaxies, clusters of galaxies, and along the cosmic web.
From their gravity, we can infer the total mass in the Universe.
Yet multiple sources indicate that only 15% of that mass can be baryonic: made of normal matter.”
Is dark matter truly necessary? Many argued that, until we found the entirety of the normal matter in the Universe, we couldn’t be sure. The motions of galaxies, clusters of galaxies, and the formation of large-scale structure and the cosmic web all indicate a certain amount of mass in the Universe, and many sources such as the CMB and big bang nucleosynthesis indicate that the “normal” matter can only be about 15% of the total, implying dark matter. But finding all the normal matter has proven elusive, with the theorized WHIM (warm-hot intergalactic medium) not showing up in sufficient abundance. In particular, the hot part just wasn’t there.
Until now. Observation made with XMM-Newton have at last revealed it, and it’s there in just the right, predicted amounts. And therefore, dark matter is still absolutely necessary.
The Counterintuitive Reason Why Dark Energy Makes The Universe Accelerate
“In a nutshell, a new form of energy can affect the Universe’s expansion rate in a new way. It all depends on how the energy density changes over time. While matter and radiation get less dense as the Universe expands, space is still space, and still has the same energy density everywhere. The only thing that’s changed is our automatic assumption that we made: that energy ought to be zero. Well, the accelerating Universe tells us it isn’t zero. The big challenge facing astrophysicists now is to figure out why it has the value that it does. On that front, dark energy is still the biggest mystery in the Universe.”
There are lots of explanations out there for why the Universe’s expansion is accelerating. Some people point towards the negative pressure of a cosmological constant and talk about how this causes space to fly apart. Others call it a “fifth force” and imply that it’s a new fundamental relation that functions as some sort of anti-gravity. Neither of those explanations are correct, though, and they both complicate a much simpler (and more correct!) truth: that the Universe’s expansion rate is simply determined by all the different types of matter and energy within it. Dark energy is just another type of energy, but it’s different in a very particular way from the normal matter, dark matter, neutrinos, and radiation that we know.
Dark energy makes the Universe accelerate because of how it evolves and changes differently from everything else we know of over time. Come find out how!
Meet The Universe’s First-Ever Supermassive Binary Black Holes
“In 1891, the object OJ 287, 3.5 billion light years distant and a blazar itself, optically bursted. Every 11-12 years since, it’s produced another burst, recently discovered to have two, narrowly-separated peaks. Its central, supermassive black hole is 18 billion solar masses, one of the largest known in the Universe. This periodic double-burst arises from a 100-150 million solar mass black hole punching through the primary’s accretion disk.”
The big problem with black holes is that, well, they’re so dark. They don’t emit any detectable light of their own, so we have to rely on indirect, secondary signals to infer their existence. That usually arises in the form of radio and X-ray radiation from matter that gets accelerated by the black hole’s extreme gravity, as well as from the magnetic fields that an accretion disk around the black hole can create. The radiation can form jets, and when a jet points at our eyes, we see a blazar. Well, the system OJ 287 has a periodic blazar that flares in a double-burst every 11-12 years, indicative of a large, supermassive black hole orbiting an even more massive behemoth, punching through the accretion disk twice with every orbit.
Come meet OJ 287, first found to burst way back in 1891, and still one of only two supermassive black hole binaries known in the Universe!
The Surprising Reason Why Neutron Stars Don’t All Collapse To Form Black Holes
“The measurements of the enormous pressure inside the proton, as well as the distribution of that pressure, show us what’s responsible for preventing the collapse of neutron stars. It’s the internal pressure inside each proton and neutron, arising from the strong force, that holds up neutron stars when white dwarfs have long given out. Determining exactly where that mass threshold is just got a great boost. Rather than solely relying on astrophysical observations, the experimental side of nuclear physics may provide the guidepost we need to theoretically understand where the limits of neutron stars actually lie.”
If you take a large, massive collection of matter and compress it down into a small space, it’s going to attempt to form a black hole. The only thing that can stop it is some sort of internal pressure that pushes back. For stars, that’s thermal, radiation pressure. For white dwarfs, that’s the quantum degeneracy pressure from the electrons. And for neutron stars, there’s quantum degeneracy pressure between the neutrons (or quarks) themselves. Only, if that last case were the only factor at play, neutron stars wouldn’t be able to get more massive than white dwarfs, and there’s strong evidence that they can reach almost twice the Chandrasekhar mass limit of 1.4 solar masses. Instead, there must be a big contribution from the internal pressure each the individual nucleon to resist collapse.
For the first time, we’ve measured that pressure distribution inside the proton, paving the way to understanding why massive neutron stars don’t all form black holes.
New Stars Turn Galaxies Pink, Even Though There Are No ‘Pink Stars’
“New star-forming regions produce lots of ultraviolet light, which ionizes atoms by kicking electrons off of their nuclei.
These electrons then find other nuclei, creating neutral atoms again, eventually cascading down through its energy levels.
Hydrogen is the most common element in the Universe, and the strongest visible light-emitting transition is at 656.3 nanometers.
The combination of this red emission line — known as the Balmer alpha (or Hα) line — with white starlight adds up to pink.”
When you look through a telescope’s eyepiece at a distant galaxy, it will always appear white to you. That’s because, on average, starlight is white, and your eyes are more sensitive to white light than any color in particular. But with the advent of a CCD camera, collecting individual photons one-at-a-time, you can more accurately gauge an astronomical object’s natural color. Even though new stars are predominantly blue in color, star-forming regions and galaxies appear pink. The problem compounds itself when you realize there isn’t any such thing as a pink star! And yet, there’s a straightforward physical explanation for what we see.
It’s a combination of ultraviolet radiation, white starlight, and the physics of hydrogen atoms that turn galaxies pink. Find out how, with some incredible visuals, today!