The first image revealed from NASA's James Webb Space Telescope on July 11 isn't just the deepest and sharpest infrared glimpse that humans have of the distant universe so far. It's also a peek at 4.6 billion years into the past.

"Whenever we look at a picture of something in the universe, we are looking back in time, because light travels at a finite speed," NASA Ames astrophysicist Dr. Thomas P. Greene, a co-investigator on the NIRCam and MIRI science instruments of the Webb Telescope, said in an interview. "Space is big, light is fast, but it's not infinitely fast."

Light from the moon is delayed about 2.5 seconds, Greene said. When you look up at the sun, you're seeing what the center of our solar system looked like nine minutes ago. But the galaxy cluster SMACS 0723, known as Webb's First Deep Field and whose images were revealed to the public by President Joe Biden, is almost incomprehensibly old.

"The images really span a lot of different astrophysical environments, all the way from right after the Big Bang," Greene said. "Those are the really distant ones," like SMACS 0723.

Webb isn't the first telescope to show us galaxies from right after the universe's creation. The NASA Hubble Space Telescope revealed stars that are as ancient as 13 billion years old. What makes Webb remarkable is how it's bringing these galactic formations into focus — and the speed at which it's doing so.

"It's got about five times the area of its mirror (compared to) Hubble, so that means it collects five times as much light," Greene said, making Webb's images far sharper.

And while Hubble can capture infrared light at about three times redder than the human eye can see, Greene said, Webb captures light that's 30 times redder, revealing cosmic cliffs, clusters of millions of glittering young stars and distant planets in sharper detail than ever before.

Webb also works faster, thanks to its location. While Hubble orbits the Earth, Webb will orbit the Sun, about a million miles away from our home planet.

"The images show in just a few hours about the same depth that Hubble went to in weeks of observations of the deep, distant universe," Greene said. "The expansion in the wavelength, or the color range, also allows us to see many more molecules in the atmospheres of planets. Where Hubble gave us a little peek about what was going on in the universe, this is going to give us a lot more information and fundamental understanding.

The images revealed so far are just a sliver of what Webb will deliver over the next couple decades and beyond.

"It's sort of like if you go to a winery, they'll give you a little bit to taste. Just a splash in your glass," Greene said. "That's what we're getting here. We're not getting the full bottle. This is really showing what's to come with Webb. We've got maybe up to 20 years or more of observations coming out of it."