Max Tegmark died on his way to high school, almost 20 years before he wrote Our Mathematical Universe. Or he thinks he may have … in another universe. (More)

Our Mathematical Universe, Part I: How Big and How Old?

This week Morning Feature considers Max Tegmark’s book Our Mathematical Universe: My Quest for the Ultimate Nature of Reality. Today we begin with how scientists estimate the size and age of our universe. Tomorrow we’ll explore his theories on multiple universes and whether our reality is simply a mathematical structure. Saturday we’ll conclude with his proposals for a sustainable civilization, and the scientific debate about his ideas.

Max Tegmark is a professor of physics at the Massachusetts Institute of Technology, where his research focuses on astronomy and cosmology. He was born in Sweden and earned bachelor’s degrees in economics and physics in Stockholm. He then earned his Ph.D in physics at the University of California, Berkeley. He worked as a research associate at the Max-Planck-Institut für Physik in Munich, and was a Hubble Fellow and member of the Institute for Advanced Study at Princeton. He has taught at MIT since 2004, has authored over 200 technical papers, appeared on several science documentaries, and received numerous academic and research awards. He has also confirmed a prediction in Douglas Adams’ The Hitchhiker’s Guide to the Galaxy, by proving that he is less intelligent than a mouse.

Dead or alive?

Max Tegmark died in 1985, in Sweden. He was riding his bicycle to school one day and emerged from an underpass without checking for traffic. A truck slammed into him at 40 miles per hour, killing him. Or he thinks that may have happened … in another universe.

In this universe, his brain decoded electrical signals from sound waves picked up by his ears, put that together with other information about the area, and alerted him to look to his right. He looked and skidded to a stop … just as the truck roared past.

The difference in those two outcomes turns on chemical activity in the brain – whether young Max felt the sudden impulse to look to his right and stop – and that signaling involves quantum-level activity. And as we’ll see tomorrow, Dr. Tegmark argues that every possible quantum event happens in some universes.

If that’s true, then he’s not “lucky to be alive,” because he died in at least some (perhaps most!) of those other universes. Instead, he’s “lucky to be in a universe where he has survived (so far).” And so are you.

“Umm, that doesn’t make sense”

Dr. Tegmark argues that evolution predicts much of modern science shouldn’t “make sense.” Our brains evolved to understand what we could detect with our physical senses: sight, sound, smell, taste, and touch. A toddler can “make sense” of the visual stimuli received from a ball in flight and predict the ball’s path well enough to catch or (more often, at first) avoid it. Most other animals have that same mental capacity, because predicting the paths of moving objects was essential to catching food, and to not becoming food. Simply, animals without that capacity starved or were eaten.

But modern physics reaches beyond our physical senses to objects that are too tiny or too far away to see with the naked eye, or to hear, smell, taste, or touch. An intuitive understanding of objects and events we couldn’t possibly detect offered no survival advantage, so our brains didn’t evolve to “make sense” of the kinds of objects and events that appear in modern physics.

That evolutionary limitation is important, Dr. Tegmark emphasizes, because the “makes sense” test is simply not reliable when we think about general relativity, quantum mechanics, or other modern theories. The GPS app on your cell phone relies on equations of general relativity and quantum mechanics. Your phone gets signals from satellites, performs calculations, and displays where you are. And your GPS app works, so we know those equations somehow correlate to ‘reality’ … even if the science doesn’t “make sense” to you, or to the scientists themselves.

“How big is space?

Dr. Tegmark often gives talks about astronomy to young children, and at one talk a five-year-old boy asked that question. The first part of his book describes the search for that answer, one that still eludes us. Millennia ago, ‘the universe’ consisted of what you could see from where you were, what you could remember from other places you had been, and what you believed of stories others told about the places they had been that you hadn’t.

The ancient Greeks were among the first to speculate that the earth was a sphere, and in the third century BCE Eratosthenes combined measurements with mathematics to calculate that the earth was about 25,000 miles in circumference. The actual measure is 24,902 miles at the equator, so he was remarkably close.

Dr. Tegmark describes how early astronomers also used measurements and mathematics to estimate the sizes of and distances to the Sun and Moon. Their early estimates weren’t as close, sometimes because their measurements weren’t precise enough, and sometimes because they didn’t believe the results they’d calculated.

In each case, the sizes and distances were larger than they imagined possible, and Dr. Tegmark notes that has happened repeatedly since. Edwin Hubble calculated that the Andromeda galaxy was a million light-years away, but with more precise data we now know it’s three times that distance.

So how big is space? Physicists don’t know. The most distant object we’ve seen, gamma ray burst GRB 090423, is about 30 billion light-years away, although it was only 13 billion light-years away when it emitted the gamma rays that were detected in 2009. The universe has been expanding ever since the Big Bang, and the stretching of space has carried GRB 090423 along with it. Space may extend out infinitely, but we can’t see infinitely far, because …

How old is the universe?

… nothing can move through space faster than light, and our observable universe doesn’t seem to be infinitely old. We can see that it’s expanding, and based on that scientists can calculate back to when it would have been impossibly tiny. They can also measure the temperature of Cosmic Microwave Background Radiation, the echoes of the Big Bang, and calculate back to when the universe would have been impossibly hot. Based on those and other methods, they estimate the Big Bang happened 13.798±0.037 billion years ago.

And based on our understanding of how stars are created – clumps of mass-energy condensing into hydrogen atoms and then being clumped by gravity until they were dense and hot enough to begin the nuclear reaction that emits starlight – GRB 090423 may be among the earliest objects we’ll ever see. That star exploded about 500,000 years after the Big Bang, so it may have been among the very first stars to form in our universe.

All of that is mainstream astrophysics, and Dr. Tegmark helped develop one of the computer programs astronomers use to pick out the Cosmic Microwave Background from other signals. He also helped develop software to map that data. The rise of what he calls “precision cosmology” has ruled out theories that seemed promising only a few decades ago. As he notes, astronomers used to debate whether the universe was 5 billion or 20 billion years old. Now they debate whether it’s 13.76 or 13.83 billion years old. There’s still a margin of error, but it shrinks each time new and better data are found.

Tomorrow we’ll explore how these mainstream theories seem to imply some truly bizarre predictions about reality … such as whether young Max Tegmark was killed by that truck – in some universes – almost 20 years ago.

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Happy Thursday!