Inflation, Gravitational Waves, and the Multiverse
The Big Bang is one of the most mysterious events we know of in cosmology. We are still not sure about what started it or what the full implications of the event are on our universe, but rest assured that many theories are vying for dominance over it and evidence continues to mount it as the favorite. But one particular fact of the Bang may help scientists understand it with better clarity, but it could come at a price: we may live in a multiverse. And while the many worlds interpretation and string theory offer their possible outcomes for this (Berman 31), it seems like inflation will be the winner.
In 1980 Alan Guth developed the idea he called inflation. Simply put, after just a few fractions (actually, 10-34) of a second after the Big Bang happened, the universe suddenly expanded at a greater rate than the speed of light (which is allowed for since it was space that was expanding faster than the speed of light and not objects in the space). This caused the universe to be distributed rather evenly in an isotropic manner. No matter how you look at the structure of the universe, it looks the same everywhere (Berman 31, Betz "The Race").
The Door Opens...
As it turns out, a natural consequence of the inflation theory is that it can happen more than once. But since inflation is a result of the Big Bang, the implication of multiple inflations means that more than one Big Bang could have happened. Yes, more than one universe is possible according to inflation. In fact, most theories of inflation call for this ongoing creation of universes, known as eternal inflation. It would help explain why certain constants in the Universe have their value, for that would be how this Universe turned out. It would be possible to have entirely different physics in other Universes because each would form with different parameters than ours. If it turns out that eternal inflation is wrong then we would have no idea as to the mystery of the constant values. And that bugs scientists. What bothers some more than others is how this talk of a multiverse seems to conveniently explain away some physics. If it can’t be tested then why is it science? (Kramer, Moskowitz, Berman 31)
But what are the mechanics that would govern this weird state of existence? Could universes inside multiverse interact with each other or are they isolated from one another for eternity? If evidence of past collisions were not only found but recognized for what they were then it would be a landmark moment in cosmology. But what would even constitute such evidence?
The CMB to the Rescue...?
Since our universe is isotropic and it looks the same everywhere on the grand scale, any imperfections would be a sign of an event that happened after inflation, such as a collision with another universe. The cosmic microwave background (CMB), the oldest light detectable from just 380,000 years after the Big Bang, would be a perfect place to find such blemishes because it is when the Universe became transparent (that is, that light was free to travel around) and thus any imperfections in the structure of the universe would be evident at the first light and would have expanded since (Meral 34-5).
Surprisingly, an alignment of hot and cold spots is known to exist in the CMB. Named the “axis of evil” by Kate Lond and Joao Magueijo of the Imperial College London in 2005, it is an apparent stretch of hot and cold spots that just should not be there if the Universe is isotropic. Quite the dilemma we got here. Scientists hoped that it was just the low resolution of the WMAP satellite but after Planck updated the CMB readings with 100 times the resolution, there was no room for doubt. But this is not the only surprising feature we find, for a cold spot also exists and half of the CMB has larger fluctuations than the other half. The cold spot may be a result of processing errors when taking out known microwave sources, such as our own Milky Way galaxy, for when different techniques are used to remove the extra microwaves the cold spot vanishes. The jury is still out on the cold spot for now (Aron “Axis, Meral 35, O’Niell “Planck”).
None of this of course should exist, for if inflation were correct then any fluctuations should be random and not in any pattern like what we observe. Inflation was like leveling the playing field and now we have found that the odds are stacked in ways that we cannot decipher. That is, unless you choose to not use a non-conventional theory like eternal inflation, which predicts such patterns as the remnants of past collisions with other Universes. Even more curious is the idea that the axis of evil could be the result of entanglement. Yes, as in quantum entanglement which states that two particles can influence each other’s state without physically interacting. But in our case, it would be entanglement of Universes according to Laura Mersini-Houton of the University of North Carolina at Chapel Hill. Let that sink in. What happens in our Universe can influence another without us ever knowing it (and they could influence us also in return, it works both ways) (Aron, Meral 35-6).
The axis of evil could therefore be a result of a state of another Universe and the cold spot a possible collision site with another Universe. Laura’s work also shows that this influence would be responsible for dark flow, or the apparent motion of galactic clusters. But the axis of evil could also result from asymmetrical inflation or from the net rotation of the Universe (Meral 35).
The best evidence for inflation and its implications of a multiverse would be a special result of Einstein’s relativity: gravitational waves, the merger of classical and quantum physics. They act similar to waves generated from a ripple in a pond but the analogy ends there. They move at the speed of light and can travel in the vacuum of space since the waves are deformations of space-time. They are generated by anything that has mass and moves but are so minute that they can only be detected if they come from huge cosmic events like black hole mergers or say the birth of the Universe. February 2016 finally saw confirmation of direct gravity wave measurements, but what we need are those generated by inflation. However, even those waves would be too weak to detect them at this point (Castelvecchi). So what good are they in helping us with proving that inflation occurred?
A team of scientists found evidence for their existence in the light polarization of the CMB. The project was known as the Background Imaging of Cosmic Extragalactic Polarization 2, or BICEP2. For over 3 years, John Kovac led the Harvard-Smithsonian Center for Astrophysics, the University of Minnesota, Stanford University, the California Institute of Technology, and JPL team gathered observations at the Amundsen-Scott South Pole Station as they looked at about 2% of the sky. They chose this cold and barren place with great care, for it offers great viewing conditions. It is 2,800 meters above sea level which means the atmosphere is thinner and thus less obstructive to light. Additionally, the air is dry, or lacking moisture, which helps prevent microwaves from getting absorbed. Finally, it is far removed from civilization and all the radiation it emits (Ritter, Castelvecchi, Moskowitz, Berman 33).
What BICEP2 Was Hunting For
According to inflation, quantum fluctuatuations of gravity fields in space began to grow as the Universe expanded, streaching them out. In fact, some would be stretched to the point where their wavelength would be larger than the size of the Universe at that time, so the gravity wave would stretch as far as it could go before inflation stopped it and caused the gravity wave to assume a form. With space now expanding at a “normal” rate, gravity waves would compress and stretch those initial fluctuation remnants, and once the CMB went through these gravity waves it too would be compressed and stretched. This caused the CMB light to be polarized, or have amplitudes fluctuate out of synchdues to pressure differentials trapping electrons in place and thus affecting their mean free path and thus light geoing through the medium (Krauss 62-3).
This caused regions of red (compressed, hotter) and regions of blue (stretched, cooler) to form in the CMB along with either swirls of light or rings/rays of light, due to density and temperature changes. E-modes appear to be vertical or horizontal because the polarization it creates is parallel of perpendicular to the actual wave vector, hence why they form ring or emanating patterns (aka curl free). The only conditions that form these are adiabatic density fluctuations, something not predicted with current models. But B-modes are, and they appear at a 45 degree angle from the wave vector (Carlstrom).
E-modes (blue) will look like either a ring or a series of lines towards the center of a circle while a B-mode (red) will look like a spiral swirl pattern in the CMB. If we see B-modes then it implies that gravity waves were a player at inflation and that both GUT and inflation are right and the doorway to string theory, the multiverse and supersymmetry will be also but if E-modes are seen then theories will need to be revised. The stakes are high, and as this follow-up demonstrates, we will struggle with finding out for sure (Krauss 65-6).
Not too long after the BICEP2 results were released some skepticism began to spread. Science has to be! If no one challenged work then who would know if we have made progress? In this case, the skepticism was in the BICEP2 team’s removal of a big contributor of B-mode readings: dust. Yes, dust, or minute particles that roam interstellar space. The dust can get polarized by the magnetic field of the Milky Way and thus read as B-modes. Dust from other galaxies can also contribute to the overall B-mode readings (Cowen, Timmer).
It was first noted by Raphael Flauger of New York University after he noticed that 1 of the 6 corrective measures that the BICEP2 used to ensure that they were looking at CMB was not done properly. Surely the scientists had taken their time and done their homework, so that did they miss? As it turns out, the Planck and BICEP2 teams were not working together on their studies of the CMB and the BICEP2 team used a PDF from a Planck conference that showed a dust map rather than just asking the Planck team for access to their full data. This was not a finalized report however and so BICEP2 was not correctly accounting for what was really there. Of course the PDF had been accessible to the public so Kovac and his group were fine using it, but it was not the full dust story they needed (Cowen).
The Planck team did finally release the full map in February of 2015 and it turns out what BICEP2 was a clear portion of the sky was filled with interfering polarized dust and even possible carbon monoxide that would give off a possible B-mode reading. So sadly it seems likely that BICEP2’s groundbreaking find is a fluke (Timmer, Betz "The Race").
But all is not lost. The Planck dust map shows much clearer portions of the sky to look at. And new efforts are underway to look for those B-modes. In January of 2015, the Spider Telescope went on a 16-day test flight. It flies on a balloon while looking at the CMB for signs of inflation. And BICEP 3 will start in late-2015 in a renewed (and more refined) hunt (Betz).
With these in mind, a future study can go find a better location and try again, possibly confirming inflation, explaining the axis of evil, and maybe even finding that we live in the multiverse. Of course, I wonder if any of those other Earths have proven the multiverse and are pondering about us…
Aron, Jacob. “Planck Shows Almost Perfect Cosmos – Plus Axis of Evil.” NewScientist.com. Reed Business Information Ltd, 21 Mar. 2013. Web. 8 Oct. 2014.
Berman, Bob. "Multiverses: Science or Science Fiction?" Astronomy Sept. 2015: 30-1, 33. Print.
Betz, Eric. "The Race to Cosmic Dawn Heats Up." Astronomy Mar. 2016: 22, 24. Print.
---. "The Race to Cosmic Dawn Heats Up." Astronomy May 2015: 13. Print.
Carlstrom, John. “The Cosmic Microwave Background and Its Polarization.” University of Chicago.
Castelvecchi, Davide. “Gravitation Waves: Here’s Everything You Need to Know.” HuffingtonPost.com. Huffington Post, 18 Mar. 2014. Web. 13 Oct. 2014.
Cowen, Rob. “Gravitational Wave Discovery Called Into Question.” HuffingtonPost.com. Huffington Post, 19 Mar. 2014. Web. 16 Oct. 2014.
Kramer, Miriam. “Our Universe Just May Exist in a Multiverse After All, Cosmic Inflation Discovery Suggests.” HuffingtonPost.com. Huffington Post, 19 Mar. 2014. Web. 12 Oct. 2014.
Krauss, Laurence M. “A Beacon From The Big Bang.” Scientific American Oct. 2014: 65-6. Print.
Meral, Zeeya. “Cosmic Collision.” Discover Oct. 2009: 34-6. Print. 13 May 2014.
Moskowitz, Clara. “Multiverse Debate Heats Up In Wake of Gravitational Waves Findings.” HuffingtonPost.com. Huffington Post, 31 Mar. 2014. Web. 13 Oct. 2014.
---. "Our Inflated Universe." Scientific American May 2014: 14. Print.
O’Niell, Ian. “Planck’s Mystery Spot Could be An Error.” Discoverynews.com. N.p., 4 Aug. 2014. Web. 10 Oct. 2014.
Ritter, Malcom. “ ‘Cosmic Inflation’ Discovery Lends Key Support of Expanding Early Universe.” HuffingtonPost.com. Huffington Post, 17 Mar. 2014. Web. 11 Oct. 2014.
Timmer, John. “Gravitational Wave Evidence Disappears Into Dust.” ArsTechnica.com. Conde Nast, 22 Sept. 2014. Web. 17 Oct. 2014.
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