Warped Passages - Lisa Randall [213]
We’re gonna get to that place
Where we really want to go.
Bruce Springsteen
Ike XLII was ready to live large. He wanted to test the Alicxvr’s ultra-high settings of many megaparsecs, with which he could explore places beyond the Galaxy and the known universe and experience distant regions no one had ever seen before.
Ike was thrilled when the Alicxvr took him to distances 9, 12, and even 13 billion light-years away. But his excitement diminished when he tried to go farther and his signal strength fell precipitously. When he aimed for 15 billion light-years, his exploration aborted completely: he no longer received any information at all. Instead, he heard, “Message 5B73: The Horizon customer you are trying to reach is beyond your calling area. If you need assistance, please contact your local long-distance operator.”
Ike couldn’t believe his ears. It was the thirty-first century, yet his Horizon service still provided only limited coverage. When Ike tried to contact the operator, a recording said, “Please stay on the brane. Your call will be answered in the order in which it was received.” Ike suspected that the operator would never respond, and was wise enough not to wait.
The previous chapter explained why warping can emancipate an extra dimension and allow it to be infinite, yet unseen. But the infinite extra dimension is not the end of the physics story: things get even more bizarre. This chapter will explain how four-dimensional gravity (that is, with three dimension of space and one of time) can be truly a local phenomenon—gravity might look very different far away. We’ll see that not only could space appear to be four-dimensional when there are truly five dimensions, but we might be living in an isolated pocket with four-dimensional gravity inside a five-dimensional universe.
The model we’ll now consider demonstrates that, remarkable as it might seem, different regions of space can appear to have different numbers of dimensions. The physicist Andreas Karch and I found a model for spacetime in which this was the case in the course of investigating some perplexing features of localized gravity. The new and radical scenario we ended up with suggests that the reason we don’t see additional dimensions could be much more peculiar to our environment than anyone had ever believed. We could be living in a four-dimensional sinkhole in which three spatial dimensions is merely an accident of location!
Reflections
When I look back at the e-mail record from the time during which Raman and I had been collaborating, I find it a little mind-boggling how we completed our work in the midst of so many other distractions. When we began our research, I was in the process of moving from MIT to Princeton, where I was about to take a position as a professor, and I was also planning a six-month workshop in Santa Barbara for the following year. Raman, who had had several postdoctoral positions, was concerned about getting a faculty offer, so he was busy preparing talks and job applications. It was difficult to believe. He had done great work, yet I and others were trying to convince him that it would work out in the end and he shouldn’t abandon physics and search for another career. Raman was clearly meant to continue with physics and strongly deserved an excellent faculty position, yet he was having trouble finding a job.
The e-mails from the time illustrate the chaos: interesting physics issues alternate with requests for letters of recommendation, scheduling talks, arranging my Princeton housing, and some Santa Barbara conference organization. There were also a few e-mail exchanges with other physicists about our work. But not many. Although the RS2 paper was ultimately cited thousands of times and became well accepted, the work’s initial reception was mixed. It took a while before most physicists understood and believed us. A colleague tells me that at first people were waiting for someone else to find the loophole so they wouldn’t have to pay attention. Certainly at Princeton, the reaction to a talk Raman gave could