Tomorrow – Notebook LM Podcast Review
On Oct 2, 2025, Tom and Janice, our two Notebook LM and AI persona, took a hard look at Tomorrow – A Practical Guide to Time Travel by Gary Paul Bryant. Listen the podcast above or read the transcript of their conversation below.
Janice:
We’ve all looked at an old photograph, maybe lost ourselves in a memory, and eventually that thought pops up. What if we could just go back? Yeah. Is zipping through time just, you know, the stuff of science fiction? Or is there maybe a genuine scientific opportunity hidden there?
Tom: It’s a really fascinating leap, isn’t it?
Janice: Today on the Deep Dive, that’s exactly what we’re getting into.
Tom: And our focus today It’s this bold new perspective from Gary Paul Bryant’s book Tomorrow, A Practical Guide to Time Travel. This deep dive is really all about trying to move time travel off that shelf with like dragons and magic portals.
Janice: Yeah, the fantasy section.
Tom: Exactly. And put it squarely onto the lab bench.
Janice: Absolutely. Our mission is to unpack Bryant’s core argument here, to really look hard at what it would take to turn time travel into, well, a step-by-step engineering challenge, not just a dream.
Tom: And what’s interesting about Bryant’s approach, like you said, is he’s not a physicist by training.
Janice: He calls himself an inquisitive human individual, which I love.
Tom: Yeah, me too. And significantly, he actually used artificial intelligence to help him sort through all the really complex theoretical physics involved.
Janice: which is a fascinating angle in itself.
Tom: Totally. Okay. And the whole book apparently started from this simple but really provocative question. If time travel is even remotely possible, why aren’t we doing more to figure it out?
Janice: A fair question.
Tom: And that question led him down a path to a model of the universe that It changes everything about how we think about time.
Janice: Okay, so let’s get right into that. What’s the foundational idea, the core concept?
Tom: The absolute central concept is what’s known as the block universe. Sometimes people call it eternalism.
Janice: Block universe, okay.
Tom: And this is the big aha moment for a lot of people because it flips our usual idea of time completely on its head. Instead of time being like a river, you know, always flowing forward.
Janice: Right, the standard metaphor.
Tom: Imagine it more like a vast, unchanging landscape, a solid block, and every single moment past, present, and future already exists within that block all at once.
Janice: Whoa. Okay, that is a radical shift. So our feeling, our perception of time moving forward, that’s just an illusion.
Tom: Pretty much. Bryant uses the metaphor of a cosmic vinyl record. Think of it like that. Each point in the groove of that record is an instant in time. your childhood home, some distant supernova, maybe your great grandkids being born way in the future.
Janice: It’s all already pressed onto the vinyl.
Tom: Exactly. And the record itself doesn’t change. All those songs, all those moments just are. They exist simultaneously. Your consciousness, your awareness right now is like the needle moving along that groove, experiencing those moments one after the other.
Janice: So if all times already exist, what does that do to the idea of time travel?
Tom: Well, it fundamentally changes it. If all times exist, then time travel isn’t about manipulating the past somehow or forcing a future that hasn’t happened yet. It’s more like learning how to navigate to another room in the house you already live in.
Janice: The rooms are all there, the past rooms, the future rooms.
Tom: They’re all there. We just don’t know how to open the doors or find the right coordinates yet.
Janice: And this block universe idea, it’s not something Bryant just invented, right? It has actual roots in modern physics.
Tom; Oh, absolutely. Deep roots. Think back to Einstein, his special relativity in 1905. That was revolutionary.
Janice: Right. It got rid of Newton’s absolute time.
Tom: Exactly. Showed time is elastic. Simultaneity is relative. Then, just a few years later, 1908, Hermann Minkowski, who was actually Einstein’s teacher. He took it a step further. He unified space and time into this single four-dimensional thing we call space-time. He had that famous quote.
Janice: The one about space and time fading into shadows.
Tom: That’s the one. Henceforth, space by itself and time by itself are doomed to fade away into mere shadows. Only some sort of unison of the two will maintain an independent reality. He saw them as fundamentally linked.
Janice: And Einstein himself seemed to lean into this later on. I remember reading that quote after his friend died.
Tom: Yes, the Besso quote. So poignant.
Janice: The distinction between past, present and future is only a stubbornly persistent illusion. It really makes you think.
Tom: It does. And this model, the block universe, it has a really neat way of dealing with paradoxes, like the famous grandfather paradox.
Janice: Ah, yes. Going back to stop your own birth. Classic sci-fi problem.
Tom: In the block universe model, it’s simply impossible. If you did travel back in time, whatever actions you took were always part of that fixed past.
Janice: So you weren’t changing history.
Tom: You were completing it. You were playing the part you were always meant to play in that moment on the cosmic record.
Janice: That fits with the Novikov self-consistency principle, doesn’t it?
Tom: Perfectly. It basically says any actions a time traveler takes had to be consistent with the history they find themselves in. It makes time travel potentially stable, not this chaotic mess of changing timelines.
Janice: So no accidental butterfly effects wiping out civilization because you stepped on a bug.
Tom: Not in this model. No. Right. Which is a big reason Bryant focuses on it for him. Time travel needs that fixed reality to even be considered an engineering problem.
Janice: Right. Because if you look at other theories like presentism.
Tom: in presentism only the now is real. There’s literally no past or future to visit.
Janice: And the multiverse. That’s the one where you create branching timelines.
Tom: Exactly. Every choice, or maybe every time jump, splits off a whole new universe. Fascinating, sure, but it makes targeted time travel incredibly difficult, maybe impossible. You’re not navigating, you’re just jumping realities.
Janice: So the block universe provides that stable map, a place to actually go.
Tom: Precisely. It makes it, at least theoretically, an engineering challenge you can aim for.
Janice: Okay, so if time is this fixed landscape, this block, the big question becomes, how do we actually move around in it? What are the tools Bryant suggests for navigating this thing?
Tom: Well, the book points out something fundamental first. You’re already a time traveler.
Janice: Ha! Okay, fair point. One second per second.
Tom: Exactly. The real challenge is manipulating that flow. making it faster for yourself relative to others, or theoretically even reversing it.
Janice: And we actually know how to speed it up for future travel, don’t we? At least in principle.
Tom: We do. Based on Einstein’s work again, special relativity gives us time dilation through speed.
Janice: Right, the faster you go.
Tom: The slower time passes for you compared to someone stationary. If you could travel near the speed of light, say, 99.999% time would slow dramatically for you. It’s the classic twin paradox.
Janice: And we see tiny versions of this already, like with astronauts.
Tom: Yep. Astronauts on the International Space Station age just a tiny fraction slower than us down here on Earth because of their speed. Now imagine scaling that way, way up.
Janice: It’s mind bending that just going really fast could literally send you years into your own future. But speed isn’t the only thing that warps time, is it? There’s gravity too.
Tom: Exactly right. General relativity brings in gravitational time dilation. Clocks actually tick slower the closer you are to a massive object.
Janice: Like a planet or a black hole.
Tom: Precisely. We have to account for this effect with GPS satellites, for instance. They’re further from Earth’s gravity, so the clocks run slightly faster. And we need to adjust for that constantly.
Janice: So if you could get really close to a black hole, safely, somehow.
Tom: time would pass much slower for you than for someone watching from far away. Maybe hours for you, years for them. The movie Interstellar showed this really effectively.
Janice: Okay, so speed and gravity are our known labors for future travel. But what about the real sci-fi stuff? The shortcuts? Maybe even travel to the past? What theoretical paths does Bryant explore?
Tom: He gets into some really fascinating, though highly theoretical constructs. First up, wormholes.
Janice: Ah, the Einstein Rosen Bridges.
Tom; That’s them. Proposed way back in 1935. Basically theoretical tunnels or shortcuts through space-time itself. For a long time they were just mathematical ideas.
Janice: But then people started asking if we could actually use them.
Tom: Right. Physicists like Kip Thorne, Nobel Prize winner, seriously explored if they could be made traversable. The thinking is if you could somehow stabilize a wormhole and maybe accelerate one end of it to near light speed.
Janice: You’d create a time difference between the two ends.
Tom: Potentially, yes. Which could allow travel between those two points in time, possibly even into the past.
Janice: Okay, wormholes. What else is in the theoretical toolkit?
Tom: Then you have concepts like closed time-like curves, or CTCs. Sounds ominous. They’re essentially paths through space-time that loop back on themselves. Theoretically, if you could follow one, you’d end up in your own past.
Janice: And these actually pop out of Einstein’s equations.
Tom: In certain specific, usually very extreme solutions, yes. Things like the Goodall universe or around rotating black holes or inside hypothetical structures like Tipler cylinders. It suggests the geometry of space-time might allow for this.
Janice: Wow. OK. And there’s one more, the warp drive idea.
Tom: The Alcubierre Drive. This is highly speculative, but it’s a concept for warping space around a ship, contracting space in front, expanding it behind.
Janice: So the ship itself doesn’t break the light speed limit locally.
Tom: Exactly. But the bubble of space-time it’s in could effectively travel faster than light relative to the outside universe. And faster-than-light travel inherently implies possibilities for time travel, or at least extreme time dilation.
Janice: But now? And this feels like a huge but, all these incredible theoretical ideas, wormholes, CTCs, warp drives, they seem to need something really weird to work, don’t they?
Tom: They absolutely do. That’s the major hurdle. Almost all of these concepts require something called exotic matter.
Janice: Exotic matter?
Tom: Yeah. Matter with properties unlike anything we normally encounter. Specifically, matter with negative energy density or negative pressure.
Janice: Negative energy? What does that even mean?
Tom: It’s hard to wrap your head around. Think of it as needing something that pushes space-time apart rather than pulling it together like normal gravity. You’d need it to prop open a wormhole, for example, or to create that Alcubierre warp bustle.
Janice: And does anything like that actually exist?
Tom: Well, on a tiny quantum scale, we see effects that produce regions of negative energy density. The Casimir effect is the prime example. It’s real physics.
Janice: Okay, so it’s not pure fantasy.
Tom: Not pure fantasy, but the amount we can observe is minuscule. Scaling that up to the level needed to stabilize a wormhole or power a warp drive. That’s the monumental challenge. It’s like needing to lift a mountain and having only the energy from, I don’t know, a single firefly.
Janice: Right. Which brings us squarely to the power problem. What kind of energy are we talking about to bend space-time like this? It sounds astronomical.
Tom: It is. We’re talking energy levels that are almost unimaginable by today’s standards. Think of the Kardashev scale.
Janice: The scale that measures civilizations by energy use. Type 1, 2, 3.
Tom: Exactly. Type 1 harnesses the power of whole planet. Type 2, a whole star. Type 3, a whole galaxy. Humanity. We’re not even close to Type 1 yet.
Janice: So our current energy sources, nuclear fission.
Tom: Not even in the same league. Fusion power, the starfire solution that powers the sun, that’s often seen as the next big leap, the holy grail of clean energy.
Janice: And the book uses an analogy here, right? Comparing fusion’s potential impact to something like Europe’s Invictus.
Tom: Yeah, the UK’s hypersonic space plane concept with that revolutionary Sabre engine. The idea is that fusion wouldn’t just be an incremental improvement. It could be a complete paradigm shift, potentially unlocking the kind of energy densities needed for manipulating space time. It represents that kind of giant leap.
Janice: But even fusion might not be enough. What else is considered?
Tom: Beyond fusion, you get into even more speculative territory. Antimatter.
Janice: The stuff from Star Trek.
Tom: Pretty much. It offers 100% mass-to-energy conversion if you annihilate it with regular matter. That’s the ultimate energy density, the crown jewel.
Janice: But incredibly hard to make and store.
Tom: Vanishingly difficult and unbelievably expensive right now. Then there’s zero-point energy, the theoretical energy inherent in the vacuum of space itself. Vast potential energy, but we have absolutely no idea how to tap into it practically.
Janice: So maybe we don’t generate it all ourselves.
Tom: That’s another thought. Adaptive strategies. Maybe finding ways to free ride on existing cosmic phenomena, like tapping into the rotational energy of a black hole, or maybe using hypothetical cosmic strings if they exist, letting nature do some of the heavy lifting.
Janice: OK, we have a theoretical map, the block universe. We have potential tools, wormholes, maybe warp drives. We have, well, astronomical energy requirements. Now let’s get practical. Before we dream of shaking hands with Caesar, who or what do we actually send? A person. Or a machine.
Tom: That is a really critical, practical fork in the road. And the book digs into this quite a bit. The argument for sending a person Well, it’s powerful, isn’t it?
Janice: It’s the romance of it all.
Tom: Exactly. The unmatched immersive sensory experience, feeling the grit under your feet in ancient Rome, smelling the air in 1910 Paris, actually speaking the language. Humans interpret, adapt, make intuitive leaps.
Janice: It’s what we see in all the stories. H.G. Wells, Outlander, you name it.
Tom: Right. But then there’s the cost and not just financial.
Janice: You mean the danger.
Tom: Immense danger. You need complex life support, serious radiation shielding, intense psychological prep and just blending in. Imagine trying to explain your smartphone or your Gore-Tex jacket in medieval England. It could be disastrous.
Janice: Yeah. Maybe leave the tech accessories at home. So the practicalities lean heavily towards the alternative.
Tom: They really do. The case for sending a probe first is compellingly practical. It’s vastly cheaper, infinitely safer. You can scale it up, send hundreds of them. No panic attacks, no need for air or food. Probes are purely focused on the mission. Gather data. And they can be incredibly sophisticated.
Janice: What kind of capabilities are we talking? Beyond just cameras?
Tom: Oh, yeah. Think nanoscale drones, maybe, almost invisible. Visual sentries sending back high-def 360-degree views. Chemical samplers analyzing air, water, even biological samples. Maybe even using quantum entanglement to send back data instantaneously, quantum messengers. Or even trying to take quantum snapshots of the past by reading subtle signatures in the quantum vacuum.
Janice: Quantum snapshots. Wow. OK. But is there maybe a middle ground? The book mentioned a third option.
Tom: Yes. The idea of remote presence. Kind of like a sci-fi video call through time.
Janice: So you project your consciousness.
Tom: Sort of. Via some kind of advanced neural link, you could potentially inhabit a probe or maybe even a sophisticated Android avatar at the destination. Your mind goes, but your body stays safe at home.
Janice
We kind of do that now in a way. Like drone pilots or VR gamers.
Tom: Exactly. Military UAV operators, people using advanced VR with haptic feedback suits. It’s tapping into that idea of extending your presence without physically being there.
Janice: So, weighing it all up. Probes, people, or remote presence. What’s Bryant’s likely first step?
Tom: The verdict seems pretty clear. Probes are way more likely to happen first. Cheaper, safer, scalable, they get you the crucial data. But humans crave presence. That pull to experience it ourselves is strong. So maybe it’s a two-stage process. Probes go first, they scout, they map, they assess the risks. Then, maybe much later, humans follow. The motto is kind of inquire first, person later.
Janice: Right. Inquire first. OK. Now, the really tricky part. Building this thing, whatever it is, probe or craft, how on earth do you test something designed to manipulate time itself without, you know, causing some kind of catastrophe or getting irretrievably lost?
Tom: Yeah, testing the untestable. It requires extreme caution, scientific rigor, step-by-step validation, tons of redundancy. Bryant lays out a pretty thorough testing protocol, which we can kind of boil down into key phrases.
Janice: What’s phase one before you build anything real?
Tom: Simulation. Exhaustive simulation. Using quantum computers, you’d run billions, maybe trillions of virtual tests simulating the energy fields, the stress on materials, how spacetime itself behaves, potential biological effects, everything. You try to break it virtually countless times before bending any real metal.
Janice: OK, makes sense. Simulate till you drop. Then if the simulations hold up.
Tom: Then you move to unmanned physical trials, but starting incredibly small and safe. Non-biological payloads, first just sensors, atomic clocks, data recorders.
Janice: the goal is?
Tom:: The initial goal might be to achieve a tiny, measurable, closed time-like loop. Send an object, maybe just a pulse of light or some particles, and have it arrive back a microsecond before it was sent. Detect that arrival before departure with ultra-precise instruments. That’s your proof of concept.
Janice: Wow, just a fraction of a second into the past?
Tom: Exactly. Then maybe time messaging. Sending simple data, a coded neutrino beam, perhaps just milliseconds into the past. Again, low risk, focused on confirming the physics and getting feedback, building confidence piece by tiny piece.
Janice: And only much, much later, after all that works flawlessly, do you even think about sending something living.
Tom: That’s the third major phase, biological testing. And again, you start small, microbes first, then maybe plants, then simple animals. All the while, meticulously monitoring everything, cellular health, DNA integrity, effects on aging, circadian rhythms, the works. Way, way down the line. If you ever get there, it would probably involve very short jumps initially. Maybe the subject is sedated, possibly under cryogenic suspension to minimize biological shock. followed by incredibly thorough physiological and psychological checkups. It’s a very long, very cautious ladder, not a single leap.
Tom: (continues) OK, so let’s say we’ve somehow built it, tested it. Now we need to navigate. And you mentioned earlier, it’s not just about picking a date, right? The Earth itself is moving a lot.
Janice: This is absolutely critical and something most sci-fi just hand waves away.
Tom: Yeah.
Janice: Your present location in space is never the same as your past location in space.
Tom: Because the Earth is spinning.
Janice: And orbiting the sun.
Tom: And the sun is orbiting the center of the galaxy. And the galaxy itself is hurtling through the cosmos. If you just jump to, say, London, 1888, without accounting for all that movement, you wouldn’t materialize in Victorian England. You’d materialize in the cold vacuum of space where Earth used to be.
Janice: Oh, right. That’s inconvenient. It’s like trying to hit a specific snowflake in a blizzard while riding a merry-go-round on a moving train.
Tom: That’s a great analogy. So you don’t just need a date. You need incredibly precise 4D coordinates. Longitude, latitude, altitude, AND, a temporal offset, a calibrated coordinate within the entire space-time structure.
Janice: So we’d need some kind of chrono-GPS, a space-time navigation system. What would that even look like?
Tom: Bryant speculates about some amazing tools. Imagine a chronoatlas, a 4D mapping program that overlays astronomical charts, planetary positions across millennia, and historical sociopolitical data.
Janice: So you could avoid like arriving in the middle of the Black Death or a major battle.
Tom: Exactly. Maybe it includes a temporal hazard index rating locations and times for potential risks like paradox hotspots or dangerous energy fluctuations. You might even need virtual causal safe zones programmed in to prevent accidental interference with major historical events.
Janice: And navigation wouldn’t just be about plotting a course, but also understanding the destination.
Tom: Absolutely. Cultural and philosophical navigation. Just like early explorers had to learn local customs and languages, a time traveler would need tools to understand the cultural coordinates, the beliefs, symbols, social rules of the era.
Janice: Like VR training modules.
Tom: Yeah. Era simulation modules for immersive training. and maybe sophisticated AI translators, semantic compression translators that don’t just translate words, but help tailor your entire behavior and speech patterns to fit in.
Janice: But hang on. If we’re in the block universe, where everything is fixed, why do we still need to navigate so carefully if the past is set isn’t our arrival already part of it?
Tom: That’s a really sharp question. It touches on the nature of consciousness versus the nature of reality. Even if the entire space-time block is static and unchanging, our experience, our consciousness, moves through it linearly.
Janice: Ah, so the navigation is for us, for our journey through the block.
Tom: Exactly. We still perceive ourselves as making a journey from point A to point B in spacetime, even if both points already exist simultaneously in the block. So we need the tools to plot and execute that perceived journey accurately and safely within the fixed structure.
Janice: OK, we’ve talked about how the block universe neatly sidesteps things like the grandfather paradox and the butterfly effect. You can’t change the past because your actions were always part of it. But even if you can’t change history, surely time travel opens up a massive can of ethical worms, right?
Tom: Oh, absolutely. Even with self-consistency, the ethical dilemmas are profound. Take observer effects and personal identity. What happens if you meet your younger self?
Janice: Yeah, it’s always a weird one in the movies.
Tom: Are you one person in two places or two distinct entities? Does seeing your past self change your memories, your sense of who you are? Philosophers like Locke and Parfit have wrestled with personal identity for centuries. Time travel just throws gasoline on that fire.
Janice: And then there’s the huge question, who gets to control this?
Tom: ethical governance. It’s maybe the biggest issue. If time travel is possible, who holds the keys? Governments for national security. Imagine preventing attacks or staging chrono assassinations.
Janice: Or corporations insider trading from the future.
Tom: Economic manipulation on an unimaginable scale. Or maybe religious groups seeking to verify or alter historical dogma. The potential for misuse is terrifying. Brian suggests we desperately need something like a global chrono code, maybe a United Nations of Time or a Temporal Stability Council to even begin managing it.
Janice: And we haven’t even touched on the energy cost. Again, the entropy dilemma.
Tom: Right. Is it ethically justifiable to pour potentially planet-scale resources into building a time machine, maybe just for scientific curiosity? Or worse, tourism, when we have urgent problems like climate change, poverty, disease, right here, right now.
Janice: Taking a Cretaceous vacation while the present burns. Yeah, that’s a tough one.
Tom: And finally, what about legacy and memory? If the past can be revisited, observed, maybe even subtly influenced within the bounds of consistency? What happens to historical truth? Do we need temporal archives protected from interference?
Janice: It really does become a time mirror, as the book puts it, reflecting our own values, fears, ambitions.
Tom: Exactly. Will we use it wisely to learn and perhaps even guide our future? Or will it just become another tool for conflict and escape?
Janice: That is a heavy thought to end on. So okay, looking ahead, while the physicists and engineers are wrestling with exotic matter and Kardashev’s scale power, is there anything practical Bryant suggests we could do now? Something that maybe scratches that time travel itch in the meantime?
Tom: He does offer a really interesting interim solution. Something he calls a kind of way-back machine for life itself.
Janice: Okay. What does that entail?
Tom: It’s about creating a total sensory archive of our current world. Imagine combining technologies we already have or are developing rapidly.
Janice: Like what?
Tom: Take Google Street View’s visual mapping, combine that with Meta’s work on immersive VR, then add layers of advanced environmental sensor data recording everything, sense, ambient sounds, wind speed, temperature, humidity, even the local electromagnetic fields, all precisely time-stamped and geolocated.
Janice: So capturing the complete sensory experience of a place at a specific moment.
Tom: Exactly. And the key is, the pieces of this technology largely exist now. We have 360 cameras, VR headsets, sophisticated environmental sensors, massive data storage. It’s about integrating them and scaling it up.
Janice: What would be the point? Just a super detailed archive.
Tom: It would be far more than that. It would create a hyper-accurate, fully immersive record, allowing future generations, or even ourselves later, to virtually revisit that exact moment. Not just see pictures, but to walk through it, listen to it, feel the simulated air, maybe even smell the recorded scents.
Janice: A sensory buffet of the past.
Tom; That’s a great way to put it. It could genuinely satisfy some of that deep human urge to experience the past, making it feel immediate and real in a way static photos or videos can’t. And it buys time. Crucial time for the scientists to maybe crack the code of actual temporal mechanics.
Janice: It feels like a natural next step, doesn’t it? From oral stories to writing to photos, film, VR, now total sensory recording.
Tom: It’s arguably the next stage in how humanity makes the past tangible.
Janice: And so that wraps up our deep dive into Gary Paul Bryant’s Tomorrow, a practical guide to time travel. We went from thinking of time as a river to seeing it as this fixed landscape, the block universe.
Tom: We look at the wild theoretical tools, wormholes, CTCs and the mind boggling power needed.
Janice: Debated sending a person versus a probe, grappled with the nightmare of 4D navigation.
Tom: And confronted those profound ethical questions that arise if this ever becomes reality.
Janice: What really stands out from Brian’s work, I think, is that insistence. This isn’t just fantasy. It’s being framed as a potential long term scientific and engineering opportunity.
Tom: The pieces are being discussed. The fundamental questions are being asked. A roadmap, however daunting and speculative, is starting to take shape.
Janice: It really taps into that core human drive, doesn’t it? The drive to explore, to push boundaries. We crossed oceans. We flew to the moon.
Tom: The seemingly impossible sometimes just shows up late to the party, but it gets there eventually.
Janice: And maybe, just maybe, the biggest revelation from trying to build a time machine won’t be about the nature of time itself.
Tom: But more about the nature of us, our ingenuity, our curiosity, our hopes, our fears. It’s a mirror, like we said.
Janice: Absolutely. A powerful mirror indeed. So until our next deep dive, keep that curiosity alive. Keep asking those big, maybe even obscure questions.
Tom: And perhaps, listen carefully if that cosmic record needle ever seems to skip. You never know where it might drop next.
Janice: See you somewhere in the groove.