What happened immediately after the Big Bang? This is the question that astrophysicist Dan Hooper tackles in his new book, At the Edge of Time, and that he’ll be addressing tomorrow night at the American Museum of Natural History during his talk on The First Seconds of the Universe (details here). Dan Hooper is a senior scientist at the Fermi National Accelerator Laboratory and a Professor of Astronomy and Astrophysics at the University of Chicago. His research is focused on the connection between particle physics and cosmology, including topics like dark matter, dark energy, and extra dimensions.
Ahead of his upcoming talk at the AMNH, I spoke to Dan about the Big Bang, cosmic inflation, and the elusive science of dark energy and quantum mechanics…
Your upcoming talk at the AMNH is about the first seconds after the Big Bang…but what are your thoughts on the seconds before it?
As we conventionally understand our universe, there really is no such thing as “before” the Big Bang. Asking what happened before the Big Bang is like asking what lies north of the North Pole – there just isn’t anything that those words in that order represent. In the traditional Big Bang framework, time along with space came into existence with the Big Bang – they didn’t exist beforehand. That being said, there is so much that we don’t know about the very early universe that I think it would be wise for us to keep an open mind about this kind of thing. It would not at all surprise me if cosmologists 30 years from now answer this kind of question very differently from how we do today.
Your new book, At the Edge of Time, also focuses on the current theories and research about what happened immediately after the Big Bang. Why do you think those initial moments are so important? What can they tell us?
From a few seconds after the Big Bang up to the present, we have a lot of relevant observations and measurements to work with, and this collection of data leaves us confident that we understand this portion of our universe’s history reasonably well. But as we go back farther in time – into the first seconds and fractions of a second after the Big Bang – we no longer have any direct observations to rely on. There are good reasons to think that key events or transitions may have taken place during this era. Matter and energy likely interacted in ways that it no longer does, and even space and time may have behaved differently than they do in the world that we know. Almost everything could have been different during these first instants of time.
What is cosmic inflation and does it conflict with the Big Bang theory?
I wouldn’t say that inflation conflicts with the Big Bang Theory, but it does add to it. According to the original version of the Big Bang Theory, our universe expanded steadily throughout its history. But by the 1970s, it was clear that this couldn’t explain how our universe came to be so uniform and so geometrically flat (not curved). One explanation for this that was proposed in the early 1980s was that space may have expanded in a sudden burst very shortly after the Big Bang. During this brief era that we now call cosmic inflation, the volume of our universe grew by a factor of about 1075, within a span of only 10-32 seconds. Cosmologists at the time worked out that if inflation really did happen, then there should be some fairly specific features in the light that was left over from the Big Bang. When, in the decades that followed, we built telescopes that could study this light in detail, we found that these predictions were correct. This is why most cosmologists today think that inflation – or something like it – actually took place.
It is believed that dark energy – the mysterious force that’s causing the accelerated expansion of the universe – makes up three-quarters of the universe! What is the biggest challenge facing astrophysicists today who are studying dark energy and dark matter, phenomena that cannot be observed directly?
Let me answer this question in two parts, one for dark matter and another for dark energy.
After decades of measurement and debate, we are now confident that most of the matter in our universe does not consist of atoms or of any other known substances, but of something else that does not appreciably radiate, reflect, or absorb light. For the lack of a better name, we call this stuff dark matter. Over the past few decades, physicists have been engaged in an ambitious experimental program seeking to reveal what the dark matter is and how it was formed in the Big Bang. But despite initial optimism, we remain ignorant of dark matter and its nature. The experiments have performed just as designed, but have seen nothing. Dark matter has turned out to be far more elusive than we had once imagined.
In the 1990s, cosmologists carried out on an ambitious program to measure how fast our universe has been expanding over the past few billion years. To our surprise, these measurements revealed that our universe is not only expanding, but is expanding at an accelerating rate. To explain this fact, we have been forced to conclude that our universe contains vast amounts of what is known as dark energy, filling all of space and driving it apart. But our best efforts to understand this phenomenon have come up almost entirely empty-handed. We simply do not understand what dark energy is, or why it exists in our universe.
Sean Carroll recently stated that even physicists don’t understand quantum mechanics! What makes quantum mechanics so elusive and fascinating?
It’s important to understand what Sean means when he says that we don’t understand quantum mechanics. The equations that we use to calculate how quantum particles and fields behave work incredibly well – no observation or measurement has ever been shown to disagree with the predictions of quantum theory. But Sean is right that there is a great deal of disagreement about physicists about what these equations really mean, and no one knows for certain what the right interpretation is. My view – which is shared by Sean – is that the most compelling interpretation of quantum theory is that the universe exists in a combination – or superposition – of quantum states, all of which are playing out as part of reality. This is what is known as the many worlds interpretation of quantum mechanics.
You can meet Dan Hooper tomorrow night, November 4th, at the American Museum of Natural History in NYC for his talk on The First Seconds of the Universe. Details here.