MATT STRASSLER
Of Particular Significance

Did The Universe Really Begin With a Singularity?

Did the universe begin with a singularity?  A point in space and/or a moment in time where everything in the universe was crushed together, infinitely hot and infinitely densely packed?

Doesn’t the Big Bang Theory say so?

Well, let me ask you a question. Did you begin with a singularity?

Let’s see. Some decades ago, you were smaller. And then before that, you were even smaller. At some point you could fit inside your mother’s body, and if we follow time backwards, you were even much smaller than that.

If we follow your growth curve back, it would be very natural — if we didn’t know anything about biology, cells, and human reproduction — to assume that initially you were infinitesimally small… that you were created from a single point!

But that would be wrong. The mistake is obvious — it doesn’t make sense to assume that the period of rapid growth that you went through as a tiny embryo was the simple continuation of a process that extends on and on into the past, back until you were infinitely small.  Instead, there was a point where something changed… the growth began not from a point but from a single object of definite size: a fertilized egg.

The notion that the Universe started with a Big Bang, and that this Big Bang started from a singularity — a point in space and/or a moment in time where the universe was infinitely hot and dense — is not that different, really, from assuming humans begin their lives as infinitely small eggs. It’s about over-extrapolating into the past. (more…)

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POSTED BY Matt Strassler

ON March 21, 2014

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If It Holds Up, What Might BICEP2’s Discovery Mean?

Well, yesterday was quite a day, and I’m still sifting through the consequences.

First things first.  As with all major claims of discovery, considerable caution is advised until the BICEP2 measurement has been verified by some other experiment.   Moreover, even if the measurement is correct, one should not assume that the interpretation in terms of gravitational waves and inflation is correct; this requires more study and further confirmation.

The media is assuming BICEP2’s measurement is correct, and that the interpretation in terms of inflation is correct, but leading scientists are not so quick to rush to judgment, and are thinking things through carefully.  Scientists are cautious not just because they’re trained to be thoughtful and careful but also because they’ve seen many claims of discovery withdrawn or discredited; discoveries are made when humans go where no one has previously gone, with technology that no one has previously used — and surprises, mistakes, and misinterpretations happen often.

But in this post, I’m going to assume assume assume that BICEP2’s results are correct, or essentially correct, and are being correctly interpreted.  Let’s assume that [here’s a primer on yesterday’s result that defines these terms]

  • they really have detected “B-mode polarization” in the “CMB” [Cosmic Microwave Background, the photons (particles of light) that are the ancient, cool glow leftover from the Hot Big Bang]
  • that this B-mode polarization really is a sign of gravitational waves generated during a brief but dramatic period of cosmic inflation that immediately preceded the Hot Big Bang,

Then — IF BICEP2’s results were basically right and were being correctly interpreted concerning inflation — what would be the implications?

Well… Wow…  They’d really be quite amazing. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 18, 2014

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BICEP2: New Evidence Of Cosmic Inflation!

[For your reference if you can’t follow this post: My History of the Universe, and a primer to help you understand what’s going on today.]

I’m still updating this post as more information comes in and as I understand more of what’s in the BICEP2 paper and data. Talking to and listening to experts, I’d describe the mood as cautiously optimistic; some people are worried about certain weird features of the data, while others seem less concerned about them… typical when a new discovery is claimed.  I’m disturbed that the media is declaring victory before the scientific community is ready to.  That didn’t happen with the Higgs discovery, where the media was, wisely, far more patient.

The Main Data

Here’s BICEP2’s data!  The black dots at the bottom of this figure, showing evidence of B-mode polarization both at small scales (“Multipole” >> 100, where it is due to gravitational lensing of E-mode polarization) and at large scales (“Multipole” << 100, where it is potentially due to gravitational waves from a period of cosmic inflation preceding the Hot Big Bang.) All the other dots on the figure are from other experiments, including the original BICEP, which only put upper bounds on how big the B-mode polarization could be.  So all the rest of the points are previous non-detections.

From the BICEP2 paper.
From the BICEP2 paper, showing the power in B-mode polarization as a function of scale on the sky (“Multipole”).  Small multipole is large scale (and possibly due to gravitational waves) and large multiple is small scale (and due to gravitational lensing of E-mode polarization.)   The black dots are BICEP2’s detection; all other points are non-detections by previous experiments.  (Earlier discoveries of B-mode polarization at large Multipole are, for some reason, not shown on this plot.)  The leftmost 3 or 4 points are the ones that give evidence for B-mode polarization from cosmic effects, and therefore possibly for gravitational waves at early times, and therefore, possibly, for cosmic inflation preceding the Hot Big Bang!

(more…)

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POSTED BY Matt Strassler

ON March 17, 2014

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A Primer On Today’s Events

The obvious questions and their brief answers, for those wanting to know what’s going on today. If you already know roughly what’s going on and want the bottom line, read the answer to the last question.

You may want to start by reading my History of the Universe articles, or at least having them available for reference.

The expectation is that today we’re going to hear from the BICEP2 experiment.

  • What is BICEP2?

BICEP2, located at the South Pole, is an experiment that looks out into the sky to study the polarization of the electromagnetic waves that are the echo of the Hot Big Bang; these waves are called the “cosmic microwave background”.

  • What are electromagnetic waves?

Electromagnetic waves are waves in the electric and magnetic fields that are present everywhere in space.  Visible light is an electromagnetic wave, as are X-rays, radio waves, and microwaves; the only difference between these types of electromagnetic waves is how fast they wiggle and how long the distance is from one wave crest to the next.   (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 17, 2014

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My New Articles on Big Bang, Inflation, Etc.

I haven’t written in detail about the history of the universe before, but with an important announcement coming up today, it was clearly time I do so.

Let’s start from the beginning. How did the universe begin?

You may have heard that “the Big Bang theory says that the universe began with a giant explosion.” THIS IS FALSE. That’s not what the original Big Bang Theory said, and it’s certainly not what the modern form of the Big Bang Theory says. The Big Bang is not like a Big Bomb. It’s not an explosion. It’s not like a seed exploding or expanding into empty space. It’s an expansion of space itself — space that was already large. And in the modern theory of the Big Bang, the hot, dense, cooling universe that people think of as the Big Bang wasn’t even the beginning.

How did the universe begin? We haven’t the faintest idea.

That’s right; we don’t know. And that’s not surprising; we can trace the history back a long way, an amazingly long way, but at some point, what we know, or even what we can make educated guesses about, drops to zero.

Unfortunately, in books, on websites, and on many TV programs, there are many, many, many, many, many descriptions of the universe that say that the Big Bang was the beginning of the universe — that the universe started with a singularity (one which they incorrectly draw as a point in space, rather than a moment in time) — and that we know everything (or can guess everything) that happened after the beginning of the universe. Many of them even explicitly say that the Big Bang was an explosion, or they illustrate it that way — as in, for instance, Stephen Hawking’s TV special on the universe. [Sigh — How are scientists supposed to explain these ideas correctly to the public when Stephen Hawking’s own TV program shows a completely misleading video?!] This is just not true, as any serious expert will tell you.

So what do we actually know? or at least suspect?

Out of the fog of our ignorance comes the strong suspicion — not yet the certainty — that at some point in the distant past (about 13.7 billion years ago) the part of the universe that we can currently observe (let’s call it “the observable patch” of the universe) was subjected to an extraordinary event, called “inflation”.

We suspect it. We have some considerable evidence. We’re looking for more evidence. We might learn more about this any day now. Maybe today’s our day.

Stay tuned for the announcement of a “Major Discovery” out of the Harvard-Smithsonian Center for Astrophysics later today.  And then stay further tuned for the community’s interpretation of its reliability.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 17, 2014

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Getting Ready for the Cosmic News

As many of you know already, we’re expecting some very significant news Monday, presumably from the BICEP2 experiment.  The rumors seem to concern a possible observation of “B-mode polarization in the cosmic microwave background radiation”, which, to the person on the street, could mean:

It would also be cool for at least one other reason: it would be yet another indirect detection of gravitational waves, which are predicted in Einstein’s theory of gravity (but not Newton’s), just as electromagnetic waves were predicted by Maxwell’s theory of electricity and magnetism.  Note, however, it would not be the first such indirect detection; that honor belongs to this Nobel-Prize-winning measurement of the behavior of a pair of neutron stars which orbit each other, one of which is a pulsar.  (Attempts at direct detection are underway at LIGO.)

Of course, it’s possible the rumors aren’t correct, and that the implications will be completely different from what people currently expect.  But the press release announcing the Monday press conference specifically said “significant discovery”, so at least it will be interesting, one way or the other.

If you have no idea, or a limited idea, of what I just said, or if you’re not sure you have all the issues straight about the universe’s history and what “Big Bang” means, fear not: I have written the History of the Universe, designed for the non-expert.  Well, not all of the history, or all of the universe either, but the parts you’re going to want to know about for Monday’s announcement.  Those of you who are still awake are invited to read what I’ve put together and send comments about the parts that are unclear or any aspects that look incorrect.  I’ll have another post in the morning hours, and then the big announcement takes place just after noon, East Coast time.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON March 16, 2014

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