Observing the multiverse with cosmic wakes

Current theories of the origin of the Universe, including string theory, predict the existence of a multiverse with many bubble universes. These bubble universes may collide, and collisions with ours produce cosmic wakes that enter our Hubble volume, appear as unusually symmetric disks in the cosmic microwave background, and disturb large scale structure. There is preliminary evidence consistent with one or more of these disturbances on our sky. However, other sources can produce similar features in the cosmic microwave background, and so additional signals are needed to verify their extra-universal origin. Here we find, for the first time, the detailed three-dimensional shape, temperature, and polarization signals of the cosmic wake of a bubble collision consistent with current observations. The polarization pattern has distinct features that when correlated with the corresponding temperature pattern are a unique and striking signal of a bubble collision. These features represent a verifiable prediction of the multiverse paradigm and might be detected by current or future experiments. A detection of a bubble collision would confirm the existence of the multiverse, provide compelling evidence for the string theory landscape, and sharpen our picture of the Universe and its origins.

Figure 1

The difference between the actual angular profile of $\delta T/T$ as a function of ${\theta }_c$ and the Sachs-Wolfe truncated-dipole approximation. The dashed line shows the maximum extent of the disk in the Sachs-Wolfe approximation. Acoustic spreading extends the radius and alters the detailed shape of small disks.

Figure 2

Polarization for (a) ${\theta }_c\approx 10°$; (b) ${\theta }_c\approx 60°$, with $|\delta T/T|={10}^{-4}$ at center. The double peak in (b) is magnified in (c).

Figure 3

Density plot of $|Q(\theta )|$ as a function of ${\theta }_c$.

Figure 4

${\delta }_{\mathrm{cdm}}$ evolution. This wake has ${\theta }_c\approx 80°$ and $\delta T/T=-{10}^{-4}$ at CMB disk center.

Figure 5

The $3\sigma$ detectability threshold for (a) temperature $T$ for Planck (middle/red line), SPIDER (top/blue line), and CMBPol (bottom/green line) and (b) $E$-mode polarization for Planck (top/red line), SPIDER (middle/blue line), and CMBPol (bottom/green line).