Warped Passages - Lisa Randall [223]
On top of that, even if you were to try to cram more energy into that tiny region, you wouldn’t succeed. Once you’ve put that much energy inside the Planck scale length, you can’t add any more without the region expanding. That is, the black hole would grow if you added energy. So rather than making a nice tiny probe to study that distance, you would blow the region up into something bigger and never get to study it while it’s small. It would be like trying to study delicate artifacts in a museum with a fine laser beam that instead burns them up. Even in physics thought experiments, you simply never see a region that is very much tinier than the Planck scale length. The rules of physics that we know break down before you get there. Somewhere in the vicinity of the Planck scale, conventional notions of spacetime almost certainly do not apply.
Facts so bizarre cry out for a deeper explanation. One of the most important lessons of the perplexing discoveries of the last decade is likely to be that space and time have more fundamental descriptions. Ed Witten succinctly summarized the problem when he said that “space and time may be doomed.” Many leading string theorists agree: Nathan Seiberg asserted, “I am almost certain that space and time are illusions” whereas David Gross imagines that, “Very likely, space and perhaps even time have constituents; space and time could turn out to be emergent properties of a very different-looking theory.”* Unfortunately, no one yet has any idea what the nature of this more fundamental description of spacetime will turn out to be. But a deeper understanding of the fundamental nature of space and time clearly remains one of the biggest and most intriguing challenges for physicists in the coming years.
25
(In)Conclusion
It’s the end of the world as we know it (and I feel fine).
REM
Icarus Rushmore XLII used his time machine to visit the past and warn Icarus III of the disaster that awaited him should he continue driving his Porsche. Ike III was so astounded by his visitor from the future that he heeded Ike XLII’s warning. He traded in his Porsche for a Fiat and subsequently led a full, contented, and slower-paced life.
Athena was ecstatic to be reunited with her brother, and Dieter was happy to see his friend, though both of them were confused since it seemed as if Ike had never left. Athena and Dieter realized that the time travel that Ike reported to them was pure fiction. Even in dreams, the Cat never looped through time, the Rabbit never reached a stop with extra time dimensions, and the quantum detective refused to contemplate such odd behavior of time. But Athena and Dieter preferred happy endings. So they suspended disbelief and accepted Ike’s fantastic story all the same.
Despite the impressive physics developments of the last few years, we don’t yet know how to harness the force of gravity or teleport objects across space, and it’s probably too soon to invest in property in extra dimensions.40 And because we don’t know how to connect universes in which you could loop through time to the one in which we live, no one can create a time machine, and most likely no one will do so any time soon (or in the past).
But even if ideas like these remain in the realm of science fiction, we live in a wonderful and mysterious universe. Our goal is to learn how its pieces fit together and how they’ve evolved into their current state. What are the connections that we haven’t yet figured out? What are the answers to questions like those I asked in the previous chapter?
Even if we have yet to understand the ultimate origin of matter at the deepest level, I hope I’ve convinced you that we do understand many aspects of its fundamental nature on the distance