Category: multiverse

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.


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.

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.

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!

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!

Is Theoretical Physics Wasting Our Best Living Minds On Nonsense?

“The book is a wild, deep, thought-provoking read that would make any reasonable person in the field who’s still capable of introspection doubt themselves. No one likes confronting the possibility of having wasted their lives chasing a phantasm of an idea, but that’s what being a theorist is all about. You see a few pieces of an incomplete puzzle and guess what the full picture truly is; most times, you’re wrong. Perhaps, in these cases, all our guesses have been wrong. In my favorite exchange, she interviews Steven Weinberg, who draws on his vast experience in physics to explain why naturalness arguments are good guides for theoretical physicists. But he only manages to convince us that they were good ideas for the classes of problems they previously succeeded at solving. There’s no guarantee they’ll be good guideposts for the current problems; in fact, they demonstrably have not been.”

There are a slew of brilliant ideas in physics that have now become the dominant, accepted theory of what describes reality: the Standard Model. the Big Bang, General Relativity, etc. These theories are, in many ways, beautiful. They have an elegant mathematical structure, they have strong predictive power, and most importantly, they match reality. It’s that last criteria that separates them from other beautiful theories that have fallen by the wayside, such as the beautiful (but incorrect) Sakata Model. theory of Technicolor, Steady-State Model, and more. Without the experimental evidence to support them, however, are we wrongly investing our energy, intellect, and resources into beautiful, promising dead-ends? In particular, are supersymmetry, grand unification, string theory, and the multiverse exactly those dead-ends, and is following them the reason (or a symptom of) why progress has been so scarce in recent decades?

Come learn about naturalness, this possibility, and why you should buy Sabine Hossenfelder’s new book, Lost In Math, to learn more!

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.

Ask Ethan: Why Haven’t We Bumped Into Another Universe Yet?

“If the Multiverse Theory is true, shouldn’t our expanding universe have bumped into another universe by now? After all, our universe is now so large that some describe it as “infinite” in size.”

The Multiverse is one of the most fascinating ideas to arise out of the past few decades. In short, it says that our Universe, as we know it, is just one of countlessly many in a vast sea of inflating spacetime. But with all of those other Universes out there, and with all of them expanding just as our own is, shouldn’t we have collided with another one by now? And if so, where’s the evidence for it? It’s a question that needs to be taken seriously, because if we make a scientific prediction that isn’t borne out, we need to understand why. But before we ever get there, we need to understand exactly what predictions come out of our theories, including the fact that even if our Universe is infinite, that doesn’t mean there isn’t another, bigger infinity preventing us from ever colliding with another one.

Come find out why our Universe shouldn’t have bumped into another one by now, and come to better understand the Multiverse while you’re at it!

Yes, The Multiverse Is Real, But It Won’t Fix Physics

“It’s always possible to construct a contrived model that defies these generic predictions, and some scientists make a career of doing so. Writing in NPR, Sabine Hossenfelder is right to criticize that approach, stating, “Just because a theory is falsifiable doesn’t mean it’s scientific.” But just because variants of the Multiverse are falsifiable, and just because the consequences of its existence are unobservable, doesn’t mean that the Multiverse isn’t real. If cosmic inflation, General Relativity, and quantum field theory are all correct, the Multiverse likely is real, and we’re living in it.”

Is the Multiverse real? If you accept cosmic inflation, look at the observable imprints it’s left in the Universe, and place it into the context of both General Relativity and Quantum Field Theory, it’s an all-but-inescapable consequence. The evidence for cosmic inflation is overwhelming, as is the evidence for the validity of GR and QFT in the energy regimes we’re discussing. The Universe we live in ought to be just one realization of a countlessly large number of regions that have the same physical laws, constants, and properties as our own. But that’s a very different story from stating what many physicists state: that the Multiverse is the answer to all the otherwise unanswerable questions about fine-tuning that our Universe presents. Resorting to the Multiverse as your answer is equivalent to giving up on physics, and that’s a step no physicist should be eager to take.

Yes, the Multiverse is real, but that doesn’t mean it can give you anything you want at all. Come learn what it does (and doesn’t) imply over on Forbes today!

Ask Ethan: Is The Universe Finite Or Infinite?

“What I’d like to see discussed whether the universe is finite or infinite, and why it might be either. I’ve seen some limited discussion by [Sean Carroll] and [Lisa] Randall to the effect it could be either. We just don’t know.”

When it comes to the ultimate question of the size of the Universe, we have to look to greater scales than what we can possibly observe. Although we can place constraints on how big the unobservable Universe must be, coming up with a lower limit to its overall size, there’s a bigger question that we don’t yet know the answer to: is it finite in size, or is it truly infinite? Beyond what we can see, there ought to be more Universe just like our own, originating from either the same Big Bang, or possibly, if inflation is correct, from other Big Bangs at later or earlier times. And thanks to the ideas of eternal inflation, we have very, very large numbers for what’s possible as far as size goes. But there’s a long way from very large to infinite, and determining whether that’s true is a very difficult prospect.

So what can we say about the conditions under which the Universe is either finite or infinite in extent? Find out on this week’s Ask Ethan!

The Multiverse Is Inevitable, And We’re Living In It

“It’s important to recognize that the Multiverse is not a scientific theory on its own. It makes no predictions for any observable phenomena that we can access from within our own pocket of existence. Rather, the Multiverse is a theoretical prediction that comes out of the laws of physics as they’re best understood today. It’s perhaps even an inevitable consequence of those laws: if you have an inflationary Universe governed by quantum physics, this is something you’re pretty much destined to wind up with.”

It sounds like an unprovable fantasy: the idea that our Universe is just one of countless others, dotted across an eternally expanding empty space separating them. That’s generally how we picture the Multiverse, with each Universe having its own hot Big Bang distinct from every other Universe. But this isn’t simply pure speculation, but the result of a few simple facts combined: our Universe is quantum in nature, inflation gave rise to the Big Bang, and quantum fields spread out in value over time. Put those pieces together, and you’ll find that no matter how small of a region inflation starts off in, so long as you demand you get enough inflation to stretch our Universe flat, it will continue on for an eternity into the future. In some locations, inevitably, it will come to an end, giving rise to a hot Big Bang, but in many others, it will continue forever, separating the regions where inflation ends from one another for all time.

The Multiverse itself may not give rise to any observable, testable predictions, but arises as a direct consequences of other physical theories that have already been validated. Find out today why it’s inevitable.