Imagine having a telescope that could see almost 14 billion years back in time to when the universe was just forming. There is a project underway called CMB-S4 that plans to build two next-generation telescopes that will be able to do just that.
CMB-S4 is a global collaboration involving over 400 scientists from more than 100 institutions spanning 20 countries. Funding for the project is being provided by the National Science Foundation and the U.S. Department of Energy. The total cost is expected to be $800 million by the time the two telescopes become operational in the early 2030s. The National Science Foundation portion of the project is led by the University of Chicago, while the Department of Energy’s part is led by Lawrence Berkeley National Laboratory.
Why These Telescopes?
Both the science behind the project and its purpose are spectacular. The CMB-S4 telescopes are being designed to examine and map ancient light called cosmic microwave background radiation (the source of the telescopes’ name) that flooded the universe immediately after the Big Bang. The telescopes will also be searching for primordial gravitational waves and testing single-field slow-roll inflation, searching for new relics, determining neutrino masses, mapping the universe in momentum, investigating dark energy, testing general relativity on large scales, measuring the impact of baryon feedback in structure evolution and much more.
Before the Big Bang, the universe was so tiny that everything we can see today was squeezed into a space smaller than an atom. This is the smallest possible scale of the universe, called the Planck length.
During the early period after the Big Bang, the universe was filled with a fog of dense hot plasma consisting of subatomic particles. As the universe expanded, the plasma cooled enough for protons and electrons to combine into neutral atoms. Unlike hot plasma, these atoms did not scatter thermal radiation, and that allowed the universe to flow transparently and unimpeded. Today, that ancient transparency enables us to see what was happening in the early universe, back to about 370,000 years after the Big Bang.
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The Scientific Importance Of CMB-S4
I had the opportunity to discuss the CMB-S4 project with one of its originators, Dr. John Carlstrom, the Subramanyan Chandrasekhar Distinguished Service Professor in the Department of Astronomy and Astrophysics at the University of Chicago. Dr. Carlstrom is currently the director of the existing South Pole telescope. Although that telescope is technically less sophisticated than the planned CMB-S4 telescopes, it has provided the team with the experience and insights needed to design the massive scale of superconducting detectors for the new telescopes. The project team must also deal with scaling the detector readout systems and with the greatly increased volume of data that must be processed.
The National Science Foundation recently awarded $3.7 million to the University of Chicago as the first installment of a $21.4 million grant to create the final designs for the two next-generation telescopes. One of the telescopes will be located in Antarctica and the other in Chile. Antarctica was chosen because it is at the earth’s axis and allows a telescope to continuously focus on 3% of the sky for deep studies as the planet rotates. The Chile site will focus on broader areas and 60% of the sky.
Once developed, built and deployed, the CMB-S4 telescopes will each have 500,000 superconducting detectors to help in the search for telltale signs of the Big Bang and swirls of quantum fluctuations in very early space-time. If relics of primordial gravity waves exist, their interaction with the CMB will create very faint but detectable signatures that will confirm that the Big Bang and the subsequent inflation of the universe actually occurred.
The telescopes will also measure polarization in the CMB, which reveals both how the light waves are oriented and the patterns of gravitational waves created by inflation of the universe, if it occurred. Measuring CMB polarization requires highly sensitive and advanced sensors. These superconducting sensors are not like cameras that use photons of light. Superconducting sensors are more like antennas that measure the strength of light fields. The CMB light is very weak, which is why it requires 500,000 sensors to detect and map it.
Why Professor Carlstrom Is Excited About This Project
Dr. Carlstrom has been in this field for decades. He said the CMB-S4 project began in 2013. Even so, his enthusiasm is still obvious. He is still very much excited by the project and its potential to add a chapter of new knowledge about the universe.
“It’s totally amazing to be looking so far back in time to study and map the early universe,” he said. “It’s not that we are studying a time just before galaxies were formed or just before stars were formed. We will be studying a time when the first atoms were forming. And what’s even more amazing is that we can look for quantum fluctuation signatures in the CMB. This project will allow us to look at the physics of the most extreme scales that we simply cannot do with particle physics experiments on Earth.”
Dr. Carlstrom said it will also be possible to measure the amount of dark matter, ordinary matter and other material in the early universe by looking for patterns of intensity in the CMB. He explained that the telescopes will measure light from the early universe, when it was only 0.00000000000000000000000000000000001 seconds old. At that time, the entire observable universe was smaller than an atom. It is believed this light will reveal gravitational wave patterns created by the inflation of the universe, a swift expansion that happened right after the Big Bang.
“We have a clear window on a time when the universe became deionized and the first atoms were formed,” Dr. Carlstrom said. “We will be looking for patterns in the CMB to determine light’s polarization and if primordial gravitational waves created ripples in space-time. By studying waves and patterns in the CMB, we can determine the density, composition and expansion of the early universe.”
Dr. Carlstrom said that the project team will also be looking at the effects of quantum fluctuations in the CMB. Quantum physics describes quantum fluctuations as tiny variations in the energy and density of quantum fields that randomly appear and disappear. When the universe underwent a rapid expansion a fraction of a second after the Big Bang, it is believed to have stretched quantum fluctuations into massive forms, causing them to become permanent and visible. Over billions of years, the transformed fluctuations became seeds that grew into the universe’s large-scale structures consisting of stars and galaxies.
When we were wrapping up our discussion, Dr. Carlstrom said, “I’m still excited even though it’s been 10 years since we started the project. Great things have happened in that time, but I thought we’d have it built by now, so I’m really eager to finish it. The challenge is to make 500,000 superconducting detectors measure light from the early universe and control them with telescopes that we know very well. It’s amazing that we even came up with this project. The fact is that we can do it. And, when we look back in time, we are learning about our own origins.”
The Bigger Picture
Dr. Calrlstrom reminded me of what Carl Sagan had said about the universe: “The cosmos is within us. We are made of star-stuff. We are a way for the universe to know itself.”
Sagan spoke the truth. We are children of the stars. We began almost 14 billion years ago, when all the matter in the universe, including everything that makes up our bodies and our minds, was seeded by tiny quantum fluctuations that grew into the vast universe we live in today. The ambitious CMB-S4 project will help us know the universe better.
1. The CMB-S4 next-generation telescopes don’t depend on photons like regular optical telescopes. Instead, the superconducting sensors detect electromagnetic fields generated by incoming photons. The sensors change resistance when they absorb fields from the CMB light. The sensor resistance tells us how much power the field contains, and the power tells us its polarization.
2. About 370,000 years after the Big Bang is the perfect time to collect data from the CMB. That period offers a clear window for observation. Before that time, the universe contained ionized plasma that obscured any measurement attempts.
3. Neutrinos are tiny particles with no electric charge and very little mass. They can travel through matter without interacting with it, making them very hard to detect. If we could detect and measure very low-energy neutrinos, we could measure when they decoupled from the universe. That would allow us to learn about conditions and events before the CMB was released. Unfortunately, we cannot measure neutrinos. About a trillion neutrinos pass through our bodies every second and keep going unimpeded through the earth and the rest of the galaxy.
4. Before the Big Bang, the entire observable universe could fit inside something smaller than an atom. Everything could be measured by Planck length, the smallest possible size in physics and an important measurement for quantum gravity, a theory that tries to combine quantum mechanics and general relativity.
5. Data management for this project will be challenging because the new CMB-S4 telescopes will produce 1,000 times more data than existing telescopes. The project has a team that is developing a data management plan specifically to address this.
6. Mass fabrication of the superconducting detectors will utilize 500 silicon wafers with 1,000 superconducting detectors each.
7. The major technology challenge for CMB-S4 is its scale. While previous generations of instruments have used tens of thousands of detectors, the CMB-S4 project will require half a million.
8. Dr. Carlstrom emphasized that there are a lot of very good scientists who have signed on to collaborate on this project. Over 400 scientists and their students and postdocs have helped improve the project and create a lot of momentum for it. This project could not be a success without them.