Science In Action – "Stephen Hawking Gets It Right Again"

BBC World Service | Host: Roland Pease | Date: September 18, 2025

Episode Overview

This episode spotlights a landmark confirmation of Stephen Hawking’s key theory about black holes, made possible by an unprecedented observation of gravitational waves from a black hole merger. The show also covers the European Space Agency’s (ESA) adventurous new "Comet Interceptor" mission—designed to chase a yet-to-be-discovered comet—alongside a preview of the Vera Rubin Observatory’s solar system survey capabilities. Wrapping up, the episode addresses funding uncertainty for NASA’s Juno spacecraft at Jupiter and its continued scientific value.

Key Discussion Points & Insights

1. Hawking’s Black Hole Prediction Confirmed (01:50–09:26)

• Background:

  • Black holes are regions where gravity is so strong not even light escapes.
  • When two black holes merge, they create gravitational waves—ripples in spacetime detectable billions of light years away.

• Recent Event:

  • On January 14, 2025, a black hole merger produced the clearest gravitational wave signal yet, allowing scientists to test Hawking’s area theorem.

• Expert Guest:
  Alberto Vecchio (University of Birmingham), one of the hundreds credited on the discovery paper.

• Key Insights:

  • This event had a signal-to-noise ratio three times stronger than the famous original 2015 detection.
  • The two black holes, each ~30 times the mass of the Sun, spiraled together at up to 50% the speed of light before merging.

• Hawking’s Area Theorem:

  • Hawking predicted the total event horizon area after black hole mergers can never decrease—only stay the same or grow.
  • Using gravitational wave data, scientists calculated the event horizon areas before and after the merger, confirming the total did indeed increase.
  • Vecchio likened the pre-merger area to "the area of the United Kingdom" and post-merger to "the surface area of Sweden" ([09:09]).

• Notable Quote:

  “One of the remarkable discoveries made by Stephen Hawking is that black holes have an area that can never shrink in time, can only grow. And so this was a way of testing this prediction...”
  – Alberto Vecchio ([06:57])

• Memorable Explanation:

  “If you know the radius, you can work out the surface area of a football... Take a black hole, it’s exactly the same thing.”
  – Alberto Vecchio ([08:18])

2. ESA’s Comet Interceptor – Waiting for a Target (10:32–16:05)

• Mission Overview:

  • ESA plans to launch a spacecraft without a predetermined target, a first for the agency.
  • The Comet Interceptor will “wait” near the Earth-Sun L2 Lagrange point until a suitable, newly discovered comet approaches from the outer solar system.

• Expert Guest:
  Colin Snodgrass (University of Edinburgh, project scientist)

• Mission Goal:

  • Intercept a "pristine" long-period comet—its first visit since the solar system formed, fresh from the Oort Cloud.

• Mission Design:

  • Main spacecraft plus two smaller probes for high-risk, close flybys.
  • Will gather most data in a 24-hour window during close approach.

• Risks & Rewards:

  • Encounter may be at velocities up to 70 km/s; even small dust grains could destroy a probe.
  • These risks are justified by the potential to study untouched comet material up close.

• Notable Quote:

  “We're building the spacecraft and then looking for the comet.”
  – Colin Snodgrass ([10:58])

  “The peak of the activity is really, you know, a day of frantic data collection in a six-year mission.”
  – Colin Snodgrass ([15:45])

3. The Vera Rubin Observatory: A Game-Changer for Comet Discovery (16:05–22:02)

• Context:

  • Comet Interceptor’s success depends on early detection of incoming comets before they race past the Sun.
  • The Vera Rubin Observatory, just coming online, is key to this effort. It will conduct the “Legacy Survey of Space and Time” (LSST).

• Expert Guest:
  Meg Schwarm (Queen’s University Belfast, Rubin and Comet Interceptor teams)

• Capabilities:

  • Can image 45 full moons at once, surveying the night sky every three days.
  • Will enable detection of faint, distant comets months or years ahead of previous possible times.
  • Anticipated to identify thousands of new comets, with most solar system objects found in the first two years.

• Notable Quotes:

  “We're going to go sit and wait in space and hope somebody finds something for us to see. But it's really fortuitous timing ... [with] Rubin Observatory being built.”
  – Meg Schwarm ([16:51])

  “The solar system is going to completely change, at least in terms of what we know about it, over the next two years from Rubin Observatory.”
  – Meg Schwarm ([21:45])

• Memorable Moment:
  Schwarm explained the “dirty snowball” nature of comets and the challenge of detecting them before they become active ([18:05–19:53]).

4. NASA’s Juno: At the Crossroads (22:02–26:56)

• Mission Status:

  • Launched in 2016, Juno has exceeded its original goals, now operating on a mission extension.
  • Current funding for science operations ends in late September 2025.

• Expert Guest:
  Scott Bolton (Southwest Research Institute, Principal Investigator for Juno)

• Achievements:

  • Gathered data on Jupiter’s interior, atmosphere, and moons.
  • Provided the clearest evidence yet of a massive volcanic eruption on Jupiter’s moon Io.

• Future Prospects:

  • There’s a proposal for a further three-year extension (to 2028), currently under review.
  • Juno remains in good health despite harsh radiation, with resources and instrumentation functioning well.

• Financial Considerations:

  • Operating costs are in the “tens of millions” per year versus billions to build a new mission.
  • The value proposition is strong given the cost already invested.

• Notable Quotes:

  “You're leveraging an asset and you've already paid mostly for it. ... In this case, I think it probably is valuable, certainly the review of our proposal suggested that.”
  – Scott Bolton ([25:35])

  “To reproduce Juno would probably be billions and to run it each year is probably tens of millions.”
  – Scott Bolton ([26:30])

Notable Quotes & Moments (with Timestamps)

• “Black holes have also beautiful simplicity because regardless of the past history, what remains is an object that is just described by two numbers.”
  – Alberto Vecchio ([06:00])

• “You wait around for, I don't know how many years you might have to wait before you get something you want. You're then flying by, you hope that it survives the mission.”
  – Roland Pease ([15:27])

• “It's a 10 year survey, but we don't have to wait all the 10 years to find [the comets].”
  – Meg Schwarm ([21:05])

• “No, I'm waiting and, and hopeful that things will work out. We'll see.”
  – Scott Bolton, on Juno’s uncertain future ([26:56])

Segment Timestamps

| Segment | Start | End | |-------------------------------------------------------------|------------|------------| | Hawking’s Theory & Black Hole Merger | 01:50 | 09:26 | | ESA Comet Interceptor Mission w/ Colin Snodgrass | 10:32 | 16:05 | | Vera Rubin Observatory & Comet Hunting w/ Meg Schwarm | 16:05 | 22:02 | | NASA Juno Mission & Future Funding w/ Scott Bolton | 22:02 | 26:56 |

Summary Takeaway

This episode celebrates breakthroughs in gravitational wave astronomy, notably affirming Stephen Hawking’s area theorem, while also highlighting the bold, patient strategy of the Comet Interceptor and the observational might soon to be brought by the Vera Rubin Observatory. The story of Juno underscores how continued investment in long-lived missions can yield extraordinary scientific returns—as well as the sometimes precarious nature of space science funding.

The show’s tone balances scientific wonder with practical realities, offering a hopeful outlook on what the next years may reveal across the cosmos.