Ask Ethan: Can We Really Get A Universe From Nothing?
“One concept bothers me. Perhaps you can help. I see it in used many places, but never really explained. “A universe from Nothing” and the concept of negative gravity. As I learned my Newtonian physics, you could put the zero point of the gravitational potential anywhere, only differences mattered. However Newtonian physics never deals with situations where matter is created… Can you help solidify this for me, preferably on [a] conceptual level, maybe with a little calculation detail?”
You’ve very likely heard two counterintuitive things about the Universe before. One of them is that the Universe arose from nothing, and this defies our intuition about how it’s impossible to get something from nothing. The second is that we have four fundamental forces in the Universe: gravity, electromagnetism, and the strong and weak nuclear forces. So how, then, do we account for the fact that the Universe’s expansion is accelerating? Isn’t this clearly evidence for a fifth force, one with negative gravity?
Guess what? These two counterintuitive aspects of reality are related. If you understand them both, you’re one step closer to making sense of the Universe.
Could Parallel Universes Be Physically Real?
“Inflation may give us an enormously huge number of Universes that reside within a greater multiverse, but there simply aren’t enough of them to create an alternate, parallel you. The number of possible outcomes simply increases too fast for even an inflationary Universe to contain them all.
In all the multiverse, there is likely only one you. You must make this Universe count, as there is no alternate version of you. Take the dream job. Stand up for yourself. Navigate through the difficulties with no regrets, and go all-out every day of your life. There is no other Universe where this version of you exists, and no future awaiting you other than the one you live into reality. Make it count.”
Our observable Universe, as vast and enormous as it may be, is still finite. There are a finite number of galaxies containing a finite number of atoms and particles that have existed for a finite amount of time since the Big Bang. There’s an idea in quantum physics call the many-worlds interpretation, where all the various quantum outcomes that are possible actually do occur, but they simply occur in parallel Universes: where the Universe was identical to our own until a critical moment when a particular quantum decision occurred.
Does the existence of a multiverse mean there’s a Universe out there where you also exist, but made different decisions? The answer is probably no. Here’s why.
Ask Ethan: How Well Has Cosmic Inflation Been Verified?
“To what margin of error or what level of statistical significance would you say you say inflation has been verified?”
So, you’ve got an alternative theory to our best mainstream scientific ideas? Well, guess what: those are the same shoes that every scientific idea we accept today were wearing at one point in the distant past. The thing that separates them from the ideas that fell by the wayside were three remarkable feats:
1. They reproduced all the earlier successes of the previous prevailing model.
2. They resolved or explained puzzles or problems that the previous model had no sufficient answer for.
3. And, perhaps most importantly, they made new predictions that we could go out and test about the Universe, and those predictions were proven correct by the appropriate experimental or observational test.
Although most people don’t appreciate it, inflation has hurdled all three bars, and has no fewer than four spectacular predictions that have since been confirmed. Come learn how well cosmic inflation has been verified today!
This Is Why The Multiverse Must Exist
“This picture, of huge Universes, far bigger than the meager part that’s observable to us, constantly being created across this exponentially inflating space, is what the Multiverse is all about. It’s not a new, testable scientific prediction, but rather a theoretical consequence that’s unavoidable, based on the laws of physics as they’re understood today. Whether the laws of physics are identical to our own in those other Universes is unknown.
If you have an inflationary Universe that’s governed by quantum physics, a Multiverse is unavoidable. As always, we are collecting as much new, compelling evidence as we can on a continuous basis to better understand the entire cosmos. It may turn out that inflation is wrong, that quantum physics is wrong, or that applying these rules the way we do has some fundamental flaw. But so far, everything adds up. Unless we’ve got something wrong, the Multiverse is inevitable, and the Universe we inhabit is just a minuscule part of it.”
Skeptical about the Multiverse? You’re not alone. After all, how can you be confident that something must exist if the experimental, measurable, or observational evidence that’s required to validate its existence isn’t located within our observable Universe? It’s a reasonable thought, but there are ways to know something that go beyond verifying the exact phenomenon we’re looking for. This is why theoretical physics is so powerful: it not only allows you to draw conclusions about things you have not yet observed, but about things you cannot observe at all.
Come find out how, and learn why the Multiverse really must exist.
Ask Ethan: Are We Deceiving Ourselves By Searching For B-Modes From Inflation?
“I have a question about B-Modes. I’ve read Dr. Keating’s book, Losing the Nobel Prize. In the book, he details his team’s search for B-modes, and claims this would be smoking gun for inflation. Dr. Hossenfelder, in a blog post, says this isn’t true and there are other ways to produce B-modes. What is the correct view?”
Perhaps the greatest danger in science is to go out, look for a predicted effect, find it, and declare victory. Why is that such a danger? Because your idea for how the effect was generated might not be the only possibility, or even the most accurate one. If I have a wild new theory that predicts some far-distant star will have a habitable planet around it, the detection of that planet does not necessarily mean the wild new theory is correct. When it comes to the origin of the Universe, our leading theory is cosmic inflation, which predicts a B-mode polarization signature in the cosmic microwave background. Are there other ways to generate those B-mode signatures, though? And if we find them, does that mean that inflation is correct, or might that be a premature conclusion?
This is a key problem, and a hard problem, in theoretical physics. But we can say a whole lot that’s intelligent on this topic, and still be correct. Let’s find out.
One Universe Is Not Enough
“If you accept that inflation is a stage that occurred in the Universe’s past prior to the hot Big Bang, and that the Universe itself is inherently quantum in nature, the existence of a multiverse is unavoidable. Even though we cannot observe these other Universes, we can observe a huge amount of evidence for inflation, indirectly pointing to its inevitability. We can also observe a huge amount of evidence that the Universe itself is quantum, even though we have no proof that inflation itself behaves as a quantum field. If you put these pieces together, it unambiguously leads to the prediction that our Universe should be only one of countlessly many Universes, all embedded in an eternally inflating, expanding background. One Universe is not enough. Even though we cannot detect it, the prediction of a multiverse is unavoidable.”
When Carl Sagan’s Cosmos began, the first words you heard were, “The cosmos is all there is, or was, or will be.” Only… what if it weren’t? What if what we know as our cosmos, i.e., the entire Universe, were only one of countlessly many, all embedded in a strange spacetime that was continuously creating more of them? This sounds like some sort of strange speculation, but it’s actually an unavoidable consequence of two of our best theories put together: cosmic inflation and quantum physics. Combine them, and you get a multiverse.
This doesn’t mean the multiverse is the answer to all our problems; far from it. But it does mean that one Universe is not enough. Come find out why!
There Was No Big Bang Singularity
“Every time you see a diagram, an article, or a story talking about the “big bang singularity” or any sort of big bang/singularity existing before inflation, know that you’re dealing with an outdated method of thinking. The idea of a Big Bang singularity went out the window as soon as we realized we had a different state — that of cosmic inflation — preceding and setting up the early, hot-and-dense state of the Big Bang. There may have been a singularity at the very beginning of space and time, with inflation arising after that, but there’s no guarantee. In science, there are the things we can test, measure, predict, and confirm or refute, like an inflationary state giving rise to a hot Big Bang. Everything else? It’s nothing more than speculation.”
The Universe, as we observe it today, is expanding and cooling, with the overall density dropping as the volume of space increases. If we ran the clock backwards, however, instead of forwards, things would appear to contract, become denser, and grow hotter. If you go back farther and farther in time, you’d come to an epoch before there were stars and galaxies; before neutral atoms could stably form; before atomic nuclei could remain; etc. You’d go all the way back to hotter and denser states, eventually compressing all the matter and energy in the Universe into a single point: a singularity. This was the ultimate beginning of everything according to the original Big Bang: the birth of time and space.
But this picture is almost 40 years out of date, and known to be wrong. Why’s that? Come learn how we know that there was no Big Bang singularity.
What Is (And Isn’t) Scientific About The Multiverse
“In this physical Universe, it’s important to observe all that we can, and to measure every bit of knowledge we can glean. Only from the full suite of data available can we hope to ever draw valid, scientific conclusions about the nature of our Universe. Some of those conclusions will have implications that we may not be able to measure: the existence of the multiverse arises from that. But when people then contend that they can draw conclusions about fundamental constants, the laws of physics, or the values of string vacua, they’re no longer doing science; they’re speculating. Wishful thinking is no substitute for data, experiments, or observables. Until we have those, be aware that the multiverse is a consequence of the best science we have available today, but it doesn’t make any scientific predictions we can put to the test.”
The multiverse is one of the most controversial topics in science today. On the one hand, it’s a remarkable story: perhaps our Universe, even beyond what we can observe, isn’t the only one out there. Perhaps there are many others, all generated in some early, pre-Big-Bang state, all disconnected from one another. This isn’t speculation; this part of it arises by combining the two well-established theories of cosmic inflation and quantum physics. Yet if we start trying to go further, such as making statements about the laws of physics, the values of fundamental constants, or the suitability of our Universe for life, we’ve lept out of the realm of science and into wild speculation or, worse, wishful thinking.
Come find out what is (and isn’t) scientific about the multiverse, and add a little bit of nuance to something you likely already have strong opinions on!
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.