Dr Katie Mack writes:

“From a tropical rainforest to the edge of time itself, James Webb begins a voyage back to the birth of the Universe” – so went the launch narration when astronomy’s latest superpowered space explorer, the James Webb Space Telescope (JWST), lifted off from French Guiana on Christmas Day. Like most launch announcements, it employed a bit of poetic license to add to the drama. But now that JWST is settled into its orbit and sending back its first calibration images, we might well ask: what will this instrument tell us about the past, and how does that even work?

Characterising a telescope as a time machine is both over- and under-stating its abilities. The telescope itself doesn’t travel through time, but what it does is much more profound than just giving us clues about the past (as, for instance, an archeological dig, or the discovery of an ancient relic would).

Telescopes peering out to distant reaches of the Universe can see our cosmic history, directly. JWST can voyage back to “the edge of time” not by actually going anywhere, but by sending us direct images of some of the earliest moments of the Universe – showing us what it would have looked like if we had actually been there, more than 13 billion years ago, watching the first galaxies form. It’s able to do this partly because of the technology, which includes extraordinarily sensitive sensors and a 6.5-meter primary mirror, and partly because of this one weird trick enabled by Einstein’s relativity. [Continue reading…]