Learn how Hubble is measuring the expansion rate of the Universe in this new explainer from NASA's Goddard Space Flight Center.
Credit: NASA's Goddard Space Flight Center
Producer & Director: James Leigh
Editor: Lucy Lund
Director of Photography: James Ball
Additional Editing & Photography: Matthew Duncan
Executive Producers: James Leigh & Matthew Duncan
Production & Post: Origin Films
Video Credit:
Hubble Space Telescope Animation
Credit: M. Kornmesser (ESA/Hubble)
Dark Energy Expansion Graph
Credit: NASA's Goddard Space Flight Center
Dark Energy Expansion Animation
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Hubble Extreme Deep Field Fly Through
Credit: NASA, ESA, and F. Summers, L. Frattare, T. Davis, Z. Levay, and G. Bacon (Viz3D Team, STScI)
James Webb Space Telescope Animations
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Music Credit:
“Alpha and Omega” by Laurent Parisi [SACEM] via KTSA Publishing [SACEM] and Universal Production Music
“Cosmic Call” by Immersive Music (Via Shutterstock Music)
Credit: NASA's Goddard Space Flight Center
Producer & Director: James Leigh
Editor: Lucy Lund
Director of Photography: James Ball
Additional Editing & Photography: Matthew Duncan
Executive Producers: James Leigh & Matthew Duncan
Production & Post: Origin Films
Video Credit:
Hubble Space Telescope Animation
Credit: M. Kornmesser (ESA/Hubble)
Dark Energy Expansion Graph
Credit: NASA's Goddard Space Flight Center
Dark Energy Expansion Animation
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Hubble Extreme Deep Field Fly Through
Credit: NASA, ESA, and F. Summers, L. Frattare, T. Davis, Z. Levay, and G. Bacon (Viz3D Team, STScI)
James Webb Space Telescope Animations
Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Music Credit:
“Alpha and Omega” by Laurent Parisi [SACEM] via KTSA Publishing [SACEM] and Universal Production Music
“Cosmic Call” by Immersive Music (Via Shutterstock Music)
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TechTranscript
00:00When Hubble was launched, one of its main objectives was to measure the Hubble constant,
00:12the expansion rate of the universe.
00:27Beginning in the mid-2000s, around 2005, I started a project to use what are sort of
00:33the gold standard tools in astronomy for measuring distances, which is to use pulsating stars
00:40called Cepheid variables, and exploding stars called Type Ia supernovae, and of course the
00:45Hubble Space Telescope itself, and to try to make more precise measurements than had
00:49ever been made as a check on the universe.
00:53New observations from the early history of the universe, what's called the Cosmic Microwave
00:58Background, were beginning to make very precise predictions of how fast the universe ought
01:03to be expanding today, and so we wanted to follow up on that by making comparably precise
01:08measurements.
01:09First, it was the WMAP, Cosmic Microwave Background Satellite, that NASA flew in the early 2000s,
01:14and then that gave way to PLONK, the European Space Agency Satellite, that's even more precise.
01:20So by measuring the Cosmic Microwave Background, and then using a model that we call the Standard
01:26Model of Cosmology, to then extrapolate that to the present time, they determined ultimately
01:32that the universe ought to be expanding in funny units that we use, 67.4 plus or minus
01:38.5 kilometers per second per megaparsec, which roughly means the universe will double in
01:44about 10 billion years.
01:50Using the Hubble Space Telescope and some of these tools, the Cepheid Variables and
01:54the Type Ia Supernovae, we determined the local expansion rate to be about 73.0 plus
02:00or minus 1.0 kilometers per second per megaparsec, which is the most precise local or present
02:08measurement of the expansion rate.
02:10But it differs from the expected value, expected that is, by the state of the universe shortly
02:16after the Big Bang, coupled with our understanding of the universe, this cosmological model,
02:21and in fact those two now sit apart from each other by about five times their mutual error
02:26bar, which is a phenomenon we call now the Hubble Tension.
02:31To give you an analogy, it would be like if you had a small child and you measured their
02:35height when they were two years old, that would be like the Cosmic Microwave Background
02:40measurement, and then you used a model of how children grow to predict how tall they
02:45ought to end up at adulthood, and that would give you a height, and then you would actually
02:49measure when they grew up how tall they were.
02:52And so that's the comparison we're making, the present state of the measurement versus
02:56what is a very precise measurement in a younger universe, and then a model, like the growth
03:02curve of a child, to predict how tall they will be.
03:06Except unlike a child, we've seen many children grow, we have a very good understanding of
03:09that growth curve, but we've only ever seen one universe, and it's full of stuff whose
03:13nature we don't deeply understand, and so it's not crazy to think that we might be missing
03:19something in that understanding.
03:24In order to predict and really extrapolate the state of the universe from the beginning
03:28to the present day, we have to understand components of the universe, particularly two
03:33components whose nature is not well understood, but make up 96% of the universe, and that's
03:37dark matter and dark energy.
03:40Dark energy makes up about 70%, and dark matter probably makes up about 25 to 27%.
03:48And we don't really understand at a detailed level what these are exactly, we don't understand
03:52their microphysics.
03:54So in order to make these predictions, we assume that they are their most vanilla or
03:59plainest possible forms.
04:01We see this tension then, and so one possibility, not the only possibility, is that they are
04:06more complicated, that there's a more complex story, or some other aspect even that we've
04:11been missing about the universe.
04:16The Hubble Space Telescope has more or less been working on measuring the Hubble concept
04:20for its entire lifetime, about 30 years, so the original goal when it was launched was
04:25to measure it to 10% uncertainty, and I think that was successfully accomplished in the
04:29early 2000s.
04:31We're now on sort of what I would say is the second generation of measurements of the Hubble
04:35concept that are targeting closer to percent level precision, and I think Hubble, especially
04:41with its new instruments, has absolutely come through with the capabilities needed.
04:46Hubble really has delivered the quality and caliber of data that's necessary to make these
04:51measurements.