Original Link : https://medium.com/the-cosmic-companion/the-universe-may-be-a-sphere-and-thats-a-problem-d9010056bb2a

The Planck spacecraft collected significant data about the Universe, including details of radiation left over from the first light in the Universe. Image credit: NASA/JPL-Caltech

Could the Universe be a sphere, rather than flat? A new examination of data from a defunct satellite poses a mystery that could result in a cosmological crisis.

For years, cosmologists have pondered the overall shape of the Universe, developing their ideas by merging data from a wide range of studies. Doing so produced the standard cosmological model, which suggests the Universe is flat. However, a new look at the cosmic background radiation — the echo of the first light of the Universe — shows everything around us may have a closed shape, like a sphere.

The Lambda-Cold Dark Matter (LCDM) model is, currently, our best understanding of the visible Cosmos. One of the fundamental conclusions of this model is that the Universe is flat. In such a Universe, two perfectly parallel light beams sent into space would continue on forever, never meeting. This idea is accepted by many researchers, since such a model answers several questions in cosmology.

When astronomers and cosmologists attempt to understand the Universe, one of the most important pieces of evidence to consider are maps of the cosmic microwave background (CMB), the echo of the first light of the Universe. Examining these maps reveal many of the characteristics of the Universe, including approximations of the amount of dark matter and energy in the Cosmos.

Having a Ball with Cosmology

However, a new examination of maps of the CMB collected by the now-defunct Planck spacecraft shows more than a 99 percent possibility that the Universe is closed, like a sphere. In this model, two parallel beams of light would, slowly, close in on each other, and wrap around the Universe until they eventually came back around to their original starting point.

“A closed Universe can provide a physical explanation for this effect, with the Planck cosmic microwave background spectra now preferring a positive curvature at more than the 99% confidence level,” researchers write in a journal article, published in Nature Astronomy, detailing their study.

This new finding in the Planck data shows the Universe is just four percent more curved than the LCDM predicts, but this is still enough of a curve to close the Universe, and lead to a wide range of problems for cosmologists.

The map of the cosmic microwave background (CMB) as seen by the Planck spacecraft. Various colors represent very slight differences in temperatures, which led to matter clumping together into stars, galaxies, and planets. Image credit: ESA and the Planck Collaboration

Throughout the history of science, experimental data has often led to the abandonment of traditional models, and the adoption of new theories.

“The retrograde motion of the planets was fundamental to the conception of the Copernican model. Kepler’s discovery that the orbit of Mars was elliptical (and not perfectly circular as in the Copernican system), paved the way to Newton’s law of universal gravitation… the progress in our understanding of the Universe is built over unexpected anomalies,” Eleonora Di Valentino writes for Nature Astronomy.

The Universe depicted as a sphere, saddle, and flat sheet
The Universe is thought to (likely) have one of three intrinsic shapes —a closed round sphere, a negative saddle shape, or a flat sheet — and most physics leans toward the flat Universe. Image credit: NASA

Run, Run, Run, Run Away…

As astronomers study the Universe, one of the characteristics of the Universe they attempt to understand is the rate at which the Universe is expanding. There are two main methods used to determine this figure — by studying the cosmic background radiation, and by examining a special variety of stellar explosions called Type 1a supernovae. The problem with this is that details of the nature of the Cosmos determined by these two methods are sometimes radically different from each other.

However, conclusions about the nature of the Universe from the CMB agrees with data obtained through studies of the Baryon Acoustic Oscillation (BAO), pressure waves from the early Universe. This suggests to some cosmologists that refinements may be needed in our understanding of Type 1a supernovae.

As the Universe expands, galaxies further from us fly away from us at a faster rate than galaxies closer to us. This is not because we occupy any special place in the Universe — observers on any world, in any galaxy anywhere — would experience an identical effect.

The Hubble constant measures how quickly objects are receding away, at a speed dependent on their distance from our home world. However, cosmologists have, so far, been unable to agree on a value for this constant, although most figures are around 73 kilometers per second per megaparsec, where a megaparsec is 3.26 million light years from Earth. Knowing the exact value of this constant would allow cosmologist to determine the history — as well as the ultimate fate — of the Universe.

Grains in the static of the CMB get larger in models of a closed Universe, and are smallest in an open model.
Electromagnetic radiation from the CMB — the oldest light in the Universe — is also warped by the shape of space, meaning that by examining maps of the radiation, it may be possible to determine the overall form of the Universe. Image credit: NASA/WMAP Science Team

Examination of the Planck data shows a greater degree of gravitational lensing (the amount light is bent by gravity) than would be expected by the standard cosmological model. A closed Universe would explain this lensing, and would also provide an explanation for why measurements of the Hubble constant return inconsistent results.

Current technology measuring the amount of dark matter pushing the Universe apart is still inadequate to determine the rate of expansion. New experiments and instruments, like the Dark Energy Spectroscopic Instrument (DESI) at Kitt Peak outside Tucson, will examine and map the effects of dark energy around the Universe, unlocking mysteries of the Cosmos.

New instruments to measure the cosmic microwave background will be needed to reliably determine the overall shape of the Universe, answering one of the most fundamental questions about the nature of the Cosmos in which we all live.