cosmology

How Evidence for Cosmic Inflation Was Reduced to Dust

by

Many of you will have read in the last week that unfortunately (though to no one’s surprise after seeing the data from the Planck satellite in the last few months) the BICEP2 experiment’s claim of a discovery of gravitational waves from cosmic inflation has blown away in the interstellar wind. [For my previous posts on BICEP2, … Read more

Will the Higgs Boson Destroy the Universe???

by

No.

The Higgs boson is not dangerous and will not destroy the universe.

The Higgs boson is a type of particle, a little ripple in the Higgs field. [See here for the Higgs FAQ.] This lowly particle, if you’re lucky enough to make one (and at the world’s largest particle accelerator, the Large Hadron Collider, only one in a trillion proton-proton collisions actually does so) has a brief life, disintegrating to other particles in less than the time that it takes light to cross from one side of an atom to another. (Recall that light can travel from the Earth to the Moon in under two seconds.) Such a fragile creature is hardly more dangerous than a mayfly.

Anyone who says otherwise probably read Hawking’s book (or read about it in the press) but didn’t understand what he or she was reading, perhaps because he or she had not read the Higgs FAQ.

If you want to worry about something Higgs-related, you can try to worry about the Higgs field, which is “ON” in our universe, though not nearly as “on” as it could be. If someone were to turn the Higgs field OFF, let’s say as a practical joke, that would be a disaster: all ordinary matter across the universe would explode, because the electrons on the outskirts of atoms would lose their mass and fly off into space. This is not something to worry about, however. We know it would require an input of energy and can’t happen spontaneously.  Moreover, the amount of energy required to artificially turn the Higgs field off is immense; to do so even in a small room would require energy comparable to that of a typical supernova, an explosion of a star that can outshine an entire galaxy and releases the vast majority of its energy in unseen neutrinos. No one, fortunately, has a supernova in his or her back pocket. And if someone did, we’d have more immediate problems than worrying about someone wasting a supernova trying to turn off the Higgs field in a basement somewhere.

Now it would also be a disaster if someone could turn the Higgs field WAY UP… more than when your older brother turned up the volume on your stereo or MP3 player and blew out your speakers. In this case atoms would violently collapse, or worse, and things would be just as nasty as if the Higgs field were turned OFF. Should you worry about this? Well, it’s possible this could happen spontaneously, so it’s slightly more plausible. But I do mean slightly. Very slightly.

Read more

Did BICEP2 Detect Gravitational Waves Directly or Indirectly?

by

A few weeks ago there was (justified) hullabaloo following the release of results from the BICEP2 experiment, which (if correct as an experiment, and if correctly interpreted) may indicate the detection of gravitational waves that were generated at an extremely early stage in the universe (or at least in its current phase)… during a (still hypothetical but increasingly plausible) stage known as cosmic inflation.  (Here’s my description of the history of the early universe as we currently understand it, and my cautionary tale on which parts of the history are well understood (and why) and which parts are not.)

During that wild day or two following the announcement, a number of scientists stated that this was “the first direct observation of gravitational waves”.  Others, including me, emphasized that this was an “indirect observation of gravitational waves.”  I’m sure many readers noticed this discrepancy.  Who was right?

No one was wrong, not on this point anyway.  It was a matter of perspective. Since I think some readers would be interested to understand this point, here’s the story, and you can make your own judgment.

Read more

Which Parts of the Big Bang Theory are Reliable, and Why?

by

Familiar throughout our international culture, the “Big Bang” is well-known as the theory that scientists use to describe and explain the history of the universe. But the theory is not a single conceptual unit, and there are parts that are more reliable than others.

It’s important to understand that the theory — a set of equations describing how the universe (more precisely, the observable patch of our universe, which may be a tiny fraction of the universe) changes over time, and leading to sometimes precise predictions for what should, if the theory is right, be observed by humans in the sky — actually consists of different periods, some of which are far more speculative than others.  In the more speculative early periods, we must use equations in which we have limited confidence at best; moreover, data relevant to these periods, from observations of the cosmos and from particle physics experiments, is slim to none. In more recent periods, our confidence is very, very strong.

In my “History of the Universe” article [see also my related articles on cosmic inflation, on the Hot Big Bang, and on the pre-inflation period; also a comment that the Big Bang is an expansion, not an explosion!], the following figure appears, though without the colored zones, which I’ve added for this post. The colored zones emphasize what we know, what we suspect, and what we don’t know at all.

History of the Universe, taken from my article with the same title, with added color-coded measures of how confident we can be in its accuracy. In each colored zone, the degree of confidence and the observational/experimental source of that confidence is indicated. Three different possible starting points for the "Big Bang" are noted at the bottom; different scientists may mean different things by the term.
History of the Universe, taken from my article with the same title, with added color-coded measures of how confident we can be in our understanding. In each colored zone, the degree of confidence and the observational/experimental source of that confidence is indicated. Three different possible starting points for the “Big Bang” are noted at the bottom; note that individual scientists may mean different things by the term.  (Caution: there is a subtlety in the use of the words “Extremely Cold”; there are subtle quantum effects that I haven’t yet written about that complicate this notion.)

Notice that in the figure, I don’t measure time from the start of the universe.  That’s because I don’t know how or when the universe started (and in particular, the notion that it started from a singularity, or worse, an exploding “cosmic egg”, is simply an over-extrapolation to the past and a misunderstanding of what the theory actually says.) Instead I measure time from the start of the Hot Big Bang in the observable patch of the universe.  I also don’t even know precisely when the Hot Big Bang started, but the uncertainty on that initial time (relative to other events) is less than one second — so all the times I’ll mention, which are much longer than that, aren’t affected by this uncertainty.

I’ll now take you through the different confidence zones of the Big Bang, from the latest to the earliest, as indicated in the figure above.

Read more

Did The Universe Really Begin With a Singularity?

by

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.

Read more

Sean Carroll’s Higgs Book Wins a Big Prize

by

Congratulations to my friend and colleague Sean Carroll, blogger at Preposterous Universe!  For his book, The Particle at the End of the Universe, about the theoretical idea and experimental discovery of the Higgs field and its particle (the Higgs `boson‘), he has won the 2013 Royal Society Winton Prize!  Not the 3 million that you get … Read more

A First Stab at Explaining “Naturalness”

by

Arguably the two greatest problems facing particle physicists, cosmologists, string theorists, and the like are both associated with an apparent failure of a notion called “naturalness”.  Until now, I’ve mostly avoided this term on this site, because to utter the word demands an extended explanation.  After all, how could nature be unnatural, by definition? Well, … Read more

The Universe According to Planck (The Satellite)

by

The big news overnight for science was the best measurement yet of the Cosmic Microwave Background [CMB], by the Planck Satellite.  The CMB consists of  microwave photons (particles of light with microwave wavelengths) that are the tell-tale leftover glow from the universe’s hot period, the Big Bang.  These photons are almost entirely uniform across the sky, and consistent with a glowing object of temperature 2.7 degrees Kelvin (or Centigrade) [poorly written] above absolute zero, the temperature where everything moves as slowly as allowed by quantum mechanics.  (Note added: A change of 1 degree Kelvin is the same as a change of 1 degree Centigrade, but absolute zero is 0° Kelvin and -273.15° Centigrade. Centigrade and Celsius are the same.) But they aren’t quite uniform!  And those slight non-uniformities, which speak volumes about the universe, have now been read with the greatest precision ever achieved.

The Cosmic Microwave Background - as seen by Planck and WMAP. Credit: ESA and the Planck Collaboration; NASA / WMAP Science Team
The Cosmic Microwave Background – as seen by Planck and its predecessor, WMAP. Credit: ESA and the Planck Collaboration; NASA / WMAP Science Team

Today my chores prevent my writing a proper post, and it doesn’t help that Planck released over a dozen papers overnight… it will take a while to sift through this.  But the bullet points that everyone is talking about are

Read more

%d bloggers like this: