A team of scientists has proposed a new test for inflation, the theory that the universe expanded dramatically in size in just a fraction of a second just after the Big Bang. Its goal is to give insight into a question that goes back many, many years: What was the universe like before the Big Bang?
Today, our middle-aged universe looks pretty calm. Although cosmic inflation is quite known for solving some important mysteries about the structure and evolution of the universe , other theories can also explain these mysteries. In some of these theories, the state of the universe preceding the Big Bang, the so-called primordial universe, contracted rather than expanded, and the Big Bang was therefore part of a large rebound.
While rapid accelerated growth in space-time would explain what we see, science needs more than just a good idea: it needs scientific evidence that removes the arguments against and confirms the assumptions.
The team of physicists at the Center for Astrophysics | Harvard & Smithsonian (CfA) and Harvard University went back to the early universe to offer a way for these inflation models to stand out from the multitude of ideas proposed.
“The current state of inflation is that it is such a flexible idea that it cannot be falsified experimentally,” says theoretical physicist Avi Loeb of the CfA. “No matter what value is measured for some observable attribute, there are always some inflation models that can explain it.”
We have been convinced for some time that our universe is expanding, its fabric slowly spreading under the influence of some kind of strange ‘dark’ energy.
If we hit the rewind button until the universe was barely 10-43 seconds old, we hit the limit of what our knowledge of physics can handle. Before that moment, what was there? The truth is that we do not know where to start.
Doing the calculations backwards, the universe would have had a radius of 10-10 meters at the time, which is quite small, but not small enough.
Microwave background
The light echo of the early universe is still visible as a cosmic microwave background. Interestingly, this background radiation looks surprisingly uniform today.
Thermodynamics makes this observation difficult to understand. This uniformity means that the radiation moved from one end of the universe to the other, balancing out fluctuations in temperature. However, the space was expanding too fast for the light to keep up with the day. For a balancing act to be remotely feasible, the radius of the newborn universe at that critical moment had to be smaller magnitudes.
This tiny cosmos would have skyrocketed through early childhood at exponential speed.
The story fits perfectly with what we observe, but so would other explanations: “In some alternative theories, the size of the universe contracts. Some do it very slowly, while others do it very fast,” says the Harvard physicist. Zhong-Zhi Xianyu.
Was there a time before the Big Bang? Was there some kind of reverse universe? All theories are welcome but there can only be one winner.
To help decide which ones stay and which ones go, the researchers proposed the use of observable attributes that we can link to discriminatory characteristics of inflation-based models.
The challenge is knowing how to interpret such observations as a sequence of events. What is needed is some kind of standardized cosmic timestamp to unravel relevant steps, some of which could potentially rule out inflation entirely.
“If we imagine all the information we’ve learned so far about what happened before the Big Bang, then the standard clock tells us how these chips should be played, says CfA’s Xingang Chen.
The team suggests a mechanism by which quantum fluctuations can hint at sequences of events that are reflected in the patterns of vast cosmic structures. “These signals will be very subtle to detect, ” says Chen. “Cosmic microwave background radiation is one of those places, and the distribution of galaxies is another. We have already started looking for these signals and there are already some interesting candidates, but we need more data.”
Other cosmologists have also suggested looking for clues to our universe’s hidden past in the eddies of light and matter in the sky.
Some point to possible “scars” left by black holes from an earlier universe on our cosmic microwave background. Others predict that we could find signs that the physics-breaking boundary we call the Big Bang never happened.
There are many interesting ideas that explain how our universe evolved. Now we only need more data to refine until we reach the final conclusion. The truth is that future galaxy studies, such as the US-leading LSST, the European Euclid, and the recently approved NASA project, SphereX, are expected to provide high-quality data that can be used to achieve this goal. .
Reference: This research has been accepted for publication by Physical Review Letters . The preprint of this paper is available in: arxiv.org/abs/1809.02603. A related previous work can be found in: arxiv.org/abs/1509.03930.
