Tag: Observable Universe

A Two-Way Stretch, Maybe

On By rolcottIn Cosmology, Uncategorized1 Comment

“Okay, Moire, I guess I gotta go with the Big Bang happening, but I still have a problem with it making everything come from a point full of nothing.”

“Back at you, Mr Feder. I have problems with your problem. To begin with, forget about your notion of a point with zero size. There’s some reason to think the Bang started with an event sized on the order of the Planck length, 10-35 meter. That’s small, but it’s not zero.”

“I suppose, but with the whole mass of the Universe crammed in there, ain’t that a recipe for the ultimate black hole? Nothing could get outta there.”

“Nothing needs to. What’s inside is already everything, remember? Besides, there isn’t an outside — space simply doesn’t exist outside of the spacetime the Bang created. Those bell‑shaped ‘Evolution of The Universe‘ diagrams are so misleading. I say that even though I’ve used the diagram myself. It’s just a graph with Time running along the central axis and Space expanding perpendicular to that. People have prettied it up to make it cylindrical and added galaxies and such. The lines just represent how much Space has expanded since the Bang. Unfortunately, people look at the bell as a some kind of boundary with empty space outside, but that’s so wrong.”

“No outside? Hard to wrap your head around.”

“Understandable. Only physicists and mathematicians get used to thinking in those terms and mostly we do it with equations instead of trying to visualize. Our equations tell us the Universe expands at the speed of light plus a bit.”

“Wait, I thought nothing could go faster than the speed of light.”

“True, nothing can traverse space faster than light or gravity, but space itself expands. At large distances it’s doing that faster than light. We actually had to devise two different definitions of distance. ‘Co‑moving distance‘ includes the expansion. ‘Proper distance‘ doesn’t. In another couple billion years, the farthest things we can see today will be co‑moving away so fast that the photons they emit will be carried away faster than they can fly towards us. Those objects will leave our Observable Universe, the spherical bubble that encloses the objects whose light gets a chance to reach us.”

“My head hurts from the expanding. Get back to the Bang thing ’cause it was small. Too small to hold atoms I guess so how can it explode to be everything?”

“‘Expand’, not ‘explode‘ — they’re different — but good guess. The Bang’s singularity was smaller than an atom by at least a factor of 1024, but conditions were far too hot in there for atoms to exist, or nuclei, or even protons and neutrons. Informally we call it a quark soup, which is okay because we think quarks are structureless points that can cram to near‑infinite density. We don’t yet know enough Physics for good calculations of temperature, density or much of anything else.”

“That’s a lot of energy, even if it’s not particles. Which is what I’m getting at. I keep hearing you can’t create energy, just transform it, right? So where did the energy come from?”

“That’s a deep question, Mr Feder, and we don’t have an answer or hypothesis or even a firm guess. It gets down to what energy even is — we’re just barely nibbling at the edges of that one. One crazy idea I kind of like is that creating our Universe took zero energy because the process was exactly compensated for by creating an anti‑Universe whose total anti‑energy matches our total energy.”

“Whaddaya mean, anti‑Universe and anti‑energy?”

<deep breath> “You know an atom has negatively‑charged electrons bound to its positively‑charged nucleus, right? Well, the anti‑Universe I’m thinking of has that situation and everything else reversed. Positive electrons, negative nucleus, but also flipped left‑right parities for some electroweak particle interactions. Oh, and time runs backwards which is how anti‑energy becomes a thing. Our Universe and my crazy anti‑Universe emerge at Time Zero from the singularity. Then they expand in opposite directions along the Time axis. Maybe the quarks and their anti‑quarks got sorted out at the flash‑point, I dunno.”

“So there’s an anti‑me out there somewhere?”

“I wouldn’t go that far.”

~~ Rich Olcott

Question Time

On By rolcottIn Astronomy: Planetary Science, Cosmology, UncategorizedLeave a comment

Cathleen unmutes her mic. “Before we wrap up this online Crazy Theories contest with voting for the virtual Ceremonial Broom, I’ve got a few questions here in the chat box. The first question is for Kareem. ‘How about negative evidence for a pre-mammal civilization? Played-out mines, things like that.‘ Kareem, over to you.”

“Thanks. Good question but you’re thinking way too short a time period. Sixty‑six million years is plenty of time to erode the mountain a mine was burrowing into and take the mining apparatus with it.

“Here’s a different kind of negative evidence I did consider. We’re extracting coal now that had been laid down in the Carboniferous Era 300 million years ago. At first, I thought I’d proved no dinosaurs were smart enough to dig up coal because it’s still around where we can mine it. But on second thought I realized that sixty-six million years is enough time for geological upthrust and folding to expose coal seams that would have been too deeply buried for mining dinosaurs to get at. So like the Silurian Hypothesis authors said, no conclusions can be drawn.”

“Nice response, Kareem. Jim, this one’s for you. ‘You said our observable universe is 93 billion lightyears across, but I’ve heard over and over that the Universe is 14 billion years old. Did our observable universe expand faster than the speed of light?‘”

“That’s a deep space question, pun intended. The answer goes to what we mean when we say that the Hubble Flow expands the Universe. Like good Newtonian physicists, we’re used to thinking of space as an enormous sheet of graph paper. We visualize statements like, ‘distant galaxies are fleeing away from us‘ as us sitting at one spot on the graph paper and those other galaxies moving like fireworks across an unchanging grid.

“But that’s not the proper post-Einstein way to look at the situation. What’s going on is that we’re at our spot on the graph paper and each distant galaxy is at its spot, but the Hubble Flow stretches the graph paper. Suppose some star at the edge of our observable universe sent out a photon 13.7 billion years ago. That photon has been headed towards us at a steady 300000 kilometers per second ever since and it finally reached an Earth telescope last night. But in the meantime, the graph paper stretched underneath the photon until space between us and its home galaxy widened by a factor of 3.4.

“By the way, it’s a factor of 3.4 instead of 6.8 because the 93 billion lightyear distance is the diameter of our observable universe sphere, and the photon’s 13.7 billion lightyear trip is that sphere’s radius.

“Mmm, one more point — The Hubble Flow rate depends on distance and it’s really slow on the human‑life timescale. The current value of the Hubble Constant says that a point that’s 3×1019 kilometers away from us is receding at about 70 kilometers per second. To put that in perspective, Hubble Flow is stretching the Moon away from us by 3000 atom‑widths per year, or about 1/1300 the rate at which the Moon is receding because of tidal friction.”

“Nice calculation, Jim. Our final question is for Amanda. ‘Could I get to one of the other quantum tracks if I dove into a black hole and went through the singularity?‘”

“I wouldn’t want to try that but let’s think about it. Near the structure’s center gravitational intensity compresses mass-energy beyond the point that the words ‘particle’ and ‘quantum’ have meaning. All you’ve got is fields fluctuating wildly in every direction of spacetime. No sign posts, no way to navigate, you wouldn’t be able to choose an exit quantum track. But you wouldn’t be able to exit anyway because in that region the arrow of time points inward. Not a sci‑fi story with a happy ending.”

“<whew> Alright, folks, time to vote. Who presented the craziest theory? All those in favor of Kareem, click on your ‘hand’ icon. … OK. Now those voting for Jim? … OK. Now those voting for Amanda? … How ’bout that, it’s a tie. I guess for each of you there’s a parallel universe where you won the virtual Ceremonial Broom. Congratulations to all and thanks for such an interesting evening. Good night, everyone.”

~~ Rich Olcott

Worlds Enough And Time Reversed

On By rolcottIn Cosmology, General: Fun Stuff, UncategorizedLeave a comment

Cathleen unmutes her mic. “Thanks, Kareem. Our next Crazy Theory presentation is from one of my Cosmology students, Jim.”

“Thanks, Cathleen. Y’all have probably heard about how Relativity Theory and Quantum Mechanics don’t play well together. Unfortunately, people have mixed the two of them together with Cosmology to spawn lots of Crazy Theories about parallel universes. I’m going to give you a quick look at a couple of them. Fasten your seat belt, you’ll need it.

“The first theory depends on the idea that the Universe is infinitely large and we can only see part of it. Everything we can see — stars, galaxies, the Cosmic Microwave Background — they all live in this sphere that’s 93 billion lightyears across. We call it our Observable Universe. Are there stars and galaxies beyond the sphere? Almost certainly, but their light hasn’t been in flight long enough to reach us. By the same token, light from the Milky Way hasn’t traveled far enough to reach anyone outside our sphere.

“Now suppose there’s an alien astronomer circling a star that’s 93 billion lightyears away from us. It’s in the middle of its observable universe just like we’re in the middle of ours. And maybe there’s another observable universe 93 billion lightyears beyond that, and so on to infinity. Oh, by the way, it’s the same in every direction so there could be an infinite number of locally-observable universes. They’re all in the same space, the same laws of physics rule everywhere, it’s just that they’re too far apart to see each other.

“The next step is a leap. With an infinite number of observable universes all following the same physical laws, probability says that each observable universe has to have twins virtually identical to it except for location. There could be many other people exactly like you, out there billions of lightyears away in various directions, sitting in front of their screens or jogging or whatever. Anything you might do, somewhere out there there’s at least one of you doing that. Or maybe a mirror image of you. Lots of yous in lots of parallel observable universes.”

“I don’t like that theory, on two grounds. First, there’s no way to test it so it’s not science. Second, I think it plays fast and loose with the notion of infinity. There’s a big difference between ‘the Universe is large beyond anything we can measure‘ and ‘the Universe is infinite‘. If you’ve been reading Sy Moire’s stuff you’ve probably seen his axiom that if your theory contains an infinity, you’ve left out physics that would stop that. Right, Cathleen?”

Cathleen unmutes her mic. “That quote’s good, Jim.”

“Thanks, so’s the axiom. So that’s one parallel universe theory. OK, here’s another one and it doesn’t depend on infinities. The pop‑science press blared excitement about time‑reversal evidence from the ANITA experiment in Antarctica. Unfortunately, the evidence isn’t anywhere as exciting as the reporting has been.

“The story starts with neutrinos, those nearly massless particles that are emitted during many sub‑atomic reactions. ANITA is one kind of neutrino detector. It’s an array of radio receivers dangling from a helium‑filled balloon 23 miles up. The receivers are designed to pick up the radio waves created when a high‑energy neutrino interacts with glacier ice, which doesn’t happen often. Most of the neutrinos come in from outer space and tell us about solar and stellar activity. However, ANITA detected two events, so‑called ‘anomalies,’ that the scientists can’t yet explain and that’s where things went nuts.

“Almost as soon as the ANITA team sent out word of the anomalies, over three dozen papers were published with hypotheses to account for them. One paper said maybe the anomalies could be interpreted as a clue to one of Cosmology’s long‑standing questions — why aren’t there as many antiprotons as protons? A whole gang of hypotheses suggest ways that maybe something in the Big Bang directed protons into our Universe and antiprotons into a mirror universe just like ours except charges and spacetime are inverted with time running backwards. There’s a tall stack of maybes in there but the New York Post and its pop‑sci allies went straight for the Bizarro parallel universe conclusion. Me, I’m waiting for more data.”

~~ Rich Olcott