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Interview with Paul Halpern

Award-winning physicist Paul Halpern, PhD, is Professor of Physics at the University of the Sciences in Philadelphia. He is the author of twelve widely acclaimed popular science books that range from the history of particle physics to the nature of the time. In this interview he discusses some of the information given in his latest book, Edge of the Universe: A Voyage to the Cosmic Horizon and Beyond.

You can find Edge of the Universe in hardback and on Kindle at and


Lisa: Paul, many thanks for taking the time to talk with me about some of the information
you've discussed in 'Edge of the Universe'.

Paul: Lisa, my pleasure!

Lisa: Why can't we see beyond the 124 billion light years across of the observable universe?

Paul: Currently, the observable universe is 92 billion light years across, representing a sphere of about 46 billion light years in radius. These represent the current positions of parts of the universe that were potentially able to send their light to us. By analogy, this is like a football player kicking a ball toward you, hitting your feet, and then running away. If you think of a light particle as the ball, and the player as a point in space, then the extent of the observable universe represents the farthest players from whom you possibly could have received a ball.

Lisa: Why does the universe seem so smooth?

Paul: If you look at the radio sky, you observe approximately the same temperature in every direction, about the same average number of galaxies per patch, and so forth. This general sameness cannot be coincidence; all these points must have at some moment been much, much closer together. That is why astronomers think that there was a moment of inflation-extremely rapid expansion-that separated very close points. It is like smoothing a sheet's wrinkles by stretching it very quickly. Without the ultra-rapid expansion it is hard to explain the smoothness.

Lisa: In Chapter 4, you write: "Inflation took a patch of space much smaller than a proton and blew it up to the size of a baseball … the precursor of today's observable universe". How do you manage to keep your mind from completely boggling when you consider such vast scales?

Paul: Actually my mind is often boggled. A cup of coffee usually helps me forget about the immensity of space and focus on the mundane tasks at hand.

Lisa: What do you think could be the long-term impact of the discovery of the Higgs Boson?

Paul: The discovery of the Higgs boson provides the last piece to complete the puzzle that is the Standard Model of particle physics. It is a great triumph for science and justifies the building of the Large Hadron Collider. However, moving beyond the Standard Model would require the discovery of additional particles. We shall see if new particles are found in coming years that extend the Standard Model.

Lisa: One of the many subjects that I found fascinating was Linde's model of chaotic inflation and Vilenkin's model of eternal inflation, using the Heisenberg Uncertainty Principle. Could you explain this for prospective readers?

Paul: Linde showed that inflation can happen very easily, through a basic type of energy field that triggers rapid growth. Vilenkin further demonstrated that this could lead to the unlimited creation of 'bubble universes,'-each with different properties. Each universe would expand indefinitely, with its denizens unaware of the neighboring universes.

Lisa: Black holes hold a widespread fascination for the general public, to the extent that they've been central themes in several movies (The Black Hole, Event Horizon, Andromeda immediately spring to mind). Why do you think they capture our imagination so strongly? And could you explain why space and time become muddled within a black hole?

Paul: Black holes capture the imagination because they represent the extreme unknown, regions that are impossible to look within unless you actually travel inside. Space and time become muddled because they are part of the same fabric that is stretched to extreme limits.

Lisa: You discuss the research into whether our universe is a hologram, with all the information encoded on the surface. If our universe is just one of many multiverses, and some collide to create new universes (as Roger Penrose also discusses in his book 'Cycles of Time'), would that mean that the information from both universes would merge in the moment of collision?

Paul: Yes if there is a collision of universes, there would be a merger of information. The total information would be encoded on the surface of the combination.

Lisa: Your explanation of the primal quantum sea is fascinating. Could the topology of space be similar to a mobius strip? Or could our universe seem like a Flatland from another universe?

Paul: The topology of space is likely simple and unconnected, like an infinite box. However, it is possible that there could be twists, like a Mobius strip, or even doughnut-like connections that wrap around. It is also possible that space has unseen dimensions, in which case the three-dimensional universe would indeed be analogous to Flatland if seen from a higher dimension.

Lisa: What are your thoughts on OPERA's claim that in 2011 the research team measured neutrinos moving slightly faster than the speed of light?

Paul: OPERA's claim was later shown to be likely the result of experimental error. Later calculations indicated that neutrinos' speeds are consistent with light, not faster than it.

Lisa: What do you make of Stephen Hawking's monogram appearing in a portrait of the cosmos from 13 billion years ago? Could that be connected with the human mind's tendency to perceive patterns, or was it clearly identifiable to everyone who observed it?

Paul: The spotting of Stephen Hawking's monogram in the cosmic radiation background does indeed point to the mind's ability to find patterns. In that area, our brains are still able to beat computers, hence the 'CAPTCHA' codes we have to solve to enter some websites to prove we are smarter than machines in that task.

Lisa: In Chapter 11 you explain that there are no contemporary quasars, because "they represent an epoch in which galactic centers were far more turbulent". Do sightings of quasars help cosmologists to map out changing phases in the evolution of the universe?

Paul: Yes, quasars provide glimpses of a far more violent phase of the universe, early in its history, when galaxies were bubbling cauldrons of energy.

Lisa: Your books span a wide range of scientific and philosophical subjects. What initially attracted you to science? And which new discoveries do you hope to witness in your lifetime?


Paul: I started getting interested in science when I was a boy and enjoyed going to science museums, such as the Franklin Institute in Philadelphia. I was fascinated by all the push-button exhibits that made sparks fly and robots twirl.

In my lifetime, I hope science is put to good use to solve environmental problems such as global warming and make our planet healthy, peaceful and prosperous.

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