# Physicists Lisa Randall and Juan Maldacena Are Demystifying the Universe

Can you guess who these attractive people are in the picture above? A couple of guesses: former models? Nope. Titans of industry? Guess again.

If you guessed two of the most esteemed physicists of our time, who are on the cutting edge of understanding our universe, you would be correct.

Meet **Lisa Randall** and **Juan Maldacena**. Randall is the Frank B. Baird, Jr. Professor of Science on the physics faculty of Harvard University. There, she researches the elementary particles that comprise our universe, the fundamental forces to which they are subject, dimensions of space-time, the Standard Model, supersymmetry, and dark matter.

**Lisa Randall** was born in Queens, New York, attended the prestigious Stuyvesant High School, at age 18, she won first place in the 1980 Westinghouse Science Talent Search, and she received a Ph.D. from **Harvard University**. Randall is most well known for the Randall-Sundrum Theory, published in 1999 and co-written with Raman Sundrum of the University of Maryland.

The theory posits that our three-dimensional universe is floating within a surrounding ** megaverse** having four spatial dimensions. Each island universe might have different laws of physics, and each would be unable to sense the presence of the other with one notable exception - the weak tug of gravity.

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The force of gravity is orders of magnitude weaker than the three other forces of our universe — the strong force, the weak force, and the electromagnetic force.

String Theory considers that all matter and some of the carriers of force, such as photons, in our universe are comprised of tiny vibrating strings. These strings are securely anchored to our home "m-brane," however, the carrier of the force of gravity, *gravitons* aren't stuck, and they can mingle throughout the universes.

That brings us to **Juan Maldacena**. Maldacena is the Carl P. Feinberg Professor of Theoretical Physics at the Institute for Advanced Study's School of Natural Sciences. Born in Argentina, Maldacena received his Ph.D. at **Princeton University**.

Where these two preternaturally blessed people, Randall, and Maldacena, come together is in space-time.

That's where **Maldacena's holographic principle** holds sway.

In it, space-time bends and twists, producing the force of gravity, and it "maps" to a network of quantum particles that live on a gravity-free surface. The interior "universe" *projects* from the lower-dimensional boundary, just like the hologram on your credit card.

This hologram provides an example of the quantum theory of gravity.

The universe is described as an *anti-de Sitter (AdS) space* that is negatively curved, like a saddle. The farther you get from the center of the saddle, the more curves tend toward vertical, which gives AdS space its outer boundary — a surface where quantum particles interact to create the holographic universe inside.

Maldacena discovered what is called the *AdS/CFT correspondence* in 1997, and just in the last year, three physicists have made progress toward a hologram of de Sitter space.

**Xi Dong** of the University of California, Santa Barbara, described the new model as a piece of "a unified framework for quantum gravity in de Sitter [space]."

Dong, along with co-authors **Eva Silverstein** of Stanford University University and **Gonzalo Torroba** of the Bariloche Atomic Center in Argentina constructed a hologram of dS space by taking two AdS universes, cutting them, manipulating them, and gluing their boundaries together.

Dong and his co-authors made the AdS space finite by chopping off the space-time region at a large radius, and this created what is called a "Randall-Sundrum throat."

Space is still created by **a conformal field theory** that lives on its boundary, but that boundary is only a finite distance away.

By adding things from string theory, the saddle-shaped AdS spaces turned into bowl-shaped dS spaces, and the physicists then mathematically "glued" the two bowls together to form a sphere, with both hemispheres forming a single quantum system that is holographically dual to the spherical deSitter space. This construction is called **a "dS/dS correspondence."**

In the last few years, physicists have discovered that the AdS/CFT correspondence works to securely encode information in what is **a jittery quantum system**, and this quantum error correction might be how our space-time, and by extension, us, came to exist despite being created out of unreliable quantum particles.

Without **Maldacena's holographic principle**, which describes how our universe arose, and without **Randall's Randall-Sundrum theory**, which describes why the force of gravity is so much weaker in our universe, our understanding of that universe would be incomplete.

So, the next time you have a cup of coffee, eat a french fry or do anything in the space-time in which we live, you might say a thank you to Lisa Randall and Juan Maldacena. And yes, they really do look like models.