Fumfer Physics 41: Time-Reversed Black Holes and White Holes

In a late-night thought experiment, Scott Douglas Jacobsen recalls opening a quantum cosmology conference in Baku alongside Edward Witten and Leonard Susskind. He asks whether a “time-reversed” black hole could exist—like a pencil balanced on its tip for eons: lawful, but fantastically unlikely. Rick Rosner argues anomalies require a stabilizing mechanism: agency, control systems, and engineered conditions, much like quantum computers holding fragile superpositions or laboratories sustaining fusion. They extend the logic to speculative warp travel and to “white holes,” the general-relativistic time-reverse of eternal black holes, while noting the real physics ultimately hinges on horizons, entropy, and information preservation.

Scott Douglas Jacobsen: I am very tired. Imagine Baku, Azerbaijan: a quantum cosmology conference. I give the opening address. People like Edward Witten are there.

Leonard Susskind is there, too, along with other people. Susskind gives a talk on thermodynamics. Witten gives a talk on black hole thermodynamics—especially the information-theoretic aspects.

Near the end, the interesting part is the thermodynamics of what would be the time-reversal of a black hole. The intuitive picture is like a pencil balanced on its tip for eons: not forbidden by the underlying laws, but wildly improbable. Given enough time—enough random shuffling in a big enough universe—you could still have a regular thermodynamic universe running forward in time, but with a locale where you get an emergent “time-reversed” object. Is that even permissible, in those terms?

Rick Rosner: Things are only “anomalous” if there is no mechanism producing the anomaly. If you have a pencil balanced on its end for eons, it is because you have an agent or a control system balancing the frickin’ pencil. You can do all sorts of crazy things in physics if you apply conscious control and agency.

Quantum computers are basically that: extremely delicate superposed states that would normally decohere, maintained by engineered conditions—tight isolation, control, refrigeration, and error correction.

So if we needed to do something “time-reversed-looking,” and we needed to engineer it, we could try. You just need to provide the framework. Fusion is another example: fusion on Earth is an unlikely configuration of matter, but you can do it if you set up the conditions.

That is also the only hope for faster-than-light travel. I do not think it will ever be possible in practice, but for it to be possible (even as a speculative idea) you would need to engineer tremendous effects that warp spacetime—contracting space ahead and expanding it behind—so you get apparent superluminal travel without locally moving faster than light.

But you are asking what a time-reversed object in a regular universe would look like. One candidate people talk about in general relativity is a “white hole,” often described as the time-reversal counterpart of an eternal black hole: you cannot enter it from the outside; instead, matter, light, and (in principle) information can only come out.

Black holes are “black” because of the event horizon—light cannot escape once it is inside—not because “information is missing” in a simple, everyday sense. The information problem is more specific: black holes have temperature and entropy, can emit Hawking radiation, and that combination raises hard questions about how information is ultimately preserved in a quantum description.

“The universe is built from information” is a philosophical stance some people like. As physics, the safer claim is that black holes behave like thermodynamic systems, and the deep issue is how that thermodynamics meshes with quantum mechanics.

Scott Douglas Jacobsen is a blogger on Vocal with over 120 posts on the platform. He is the publisher of In-Sight Publishing (ISBN: 978–1–0692343) and the Editor-in-Chief of In-Sight: Interviews (ISSN: 2369–6885). He writes for The Good Men Project, International Policy Digest (ISSN: 2332–9416), The Humanist (Print: ISSN 0018–7399; Online: ISSN 2163–3576), Basic Income Earth Network (UK Registered Charity 1177066), A Further Inquiry, The Washington Outsider, The Rabble, and The Washington Outsider, and other media. He is a member in good standing of numerous media associations/organizations.