Around the beginning of Dragon Ball's Cell arc, a mysterious young man appears before our heroes. That young man turned out to be none other than Trunks, who had journeyed back to the present from the future! I'm sure many of you out there were enthralled by this revelation, begging to know more about him and the secrets behind the future's time machines!
Seeing Trunks travel between past, present, and future at will left us all in awe of Bulma's incredible technology, but also wondering if travelling through time could really be so simple.
So how does time travel work for us in the real world—if at all? I sat down with cosmologist Professor Toshifumi Futamase of Kyoto Sangyo University and asked him just that. We took a deep dive into the mechanics of time machines and time travel as well as the conditions required to make them possible, all in service of understanding the original series that much more!
The complexity of time travel left me scratching my head, and I was struck by a new-found appreciation for the genius Bulma demonstrated by overcoming all the obstacles and creating a fully functional time machine! But let's get to all that in chronological order—for the time being, at least. Please join us on our journey through time!
Being interviewed: Professor Toshifumi Futamase
Professor of Astrophysics & Meteorology at Kyoto Sangyo University's Faculty of Science.
Specialist in General Relativity & Cosmology.
Engaged in theoretical and observational research (using a gravity lens) of dark matter and dark matter energy.
Read Jump Comics throughout Dragon Ball's serialization.
Technical illustrator. Makes technical illustrations and illustrations for instruction manuals.
Also a proficient writer of articles that utilize her own illustration skills for websites such as Daily Portal Z.
*Interview was conducted remotely.
——In Dragon Ball, Bulma made a time machine by herself in the future. Is creating a time machine in the real world theoretically possible?
Prof. Futamase: We don't know yet. However, in physics we are yet to prove that creating a time machine is not possible. For now, let's just assume that creating a time machine is possible, shall we?
——So time machines are still in the R&D stage!
Prof. Futamase: At this time, we've confirmed that speeding up and slowing down the flow of time is possible. We can't manipulate it to a great extent yet, but we're able to speed it up and slow it down by a tiny fraction, which involves both the speed of light and gravity.
——If you watch movies about time travel, they often say that the closer to the speed of light you get, the slower time moves... but this is the first I've heard of gravity being involved.
Prof. Futamase: We'll be here all day if I go into the fine details, so I'll try to keep it brief. In General Relativity, the stronger a gravitational field is, the more warped space-time becomes around it, and the slower time moves in that area. For example, gravity on the Sun is stronger than it is on Earth, so it's believed that 1 second on the Sun is actually longer than 1 second on Earth.
——Oh, so the stronger gravity is, the slower time moves!
Prof. Futamase: In the same way, gravity around a black hole is much greater than it is on Earth, so 1 second spent in the vicinity of a black hole is equivalent to 10~20 years on Earth. So in that way, the flow of time isn't constant—it varies based on your location or the planet you're on.
——I feel like our conversation is veering closer to time machines. You already said that we don't yet know if creating a time machine is possible or not, but is it feasible for humans to travel to and from the past and future?
Prof. Futamase: Travelling to the future is theoretically not that difficult. Remember what we just said about the effects of spending time in a place with stronger gravity. Ignoring the impracticalities for now, imagine that you travelled from Earth to a black hole. You then spend just 10 seconds near said black hole and return home. Now, when you return to Earth, far more than 10 seconds have passed, and from your perspective, you've travelled forward in time.
The problem is travelling backwards in time—that's the one we haven't figured out yet. However, there's nothing to prove we can't. It's theorized that if you take an extremely small object, say, a fundamental particle, it may be possible to send it back in time.
——So it's possible with a tiny object like a fundamental particle. Which I guess means that sending humans back is...
Prof. Futamase: It's definitely a long way off. It's thought that research will progress in stages from here with items like ping-pong balls and baseballs. So with where we are now, we can only say that we don't yet know if it's possible with humans. There are research papers that delve into the creation of time machines with the central theme being "How can we travel to the past?"
——So, we can hope that civilization on Earth continues to develop technologically to the point we can send someone to a black hole for a minute or two, then that person can come back and ask the people of Earth a couple hundred years in the future how to travel back in time. Is that sort of method at all viable?
Prof. Futamase: Yes, it is. But there may already be planets that are home to civilizations far more advanced than our own somewhere in the Milky Way. So it's also conceivable that we find one such planet and ask its inhabitants about travelling back in time.
——It's just hit me all over again how incredible Bulma is for having managed to create a time machine all by herself...!
——The time machine in Dragon Ball is a kind of egg-shaped craft with stilt-like legs attached, but what sort of shape do you imagine a time machine that humans could use would be?
Prof. Futamase: It could either be a craft that's capable of surpassing the speed of light, or a physical space that bends space-time and creates a 'shortcut' through it.
——A craft that's faster than light... But hang on, I thought light was the fastest thing in the universe?
Prof. Futamase: In physics today, yes, it's believed that nothing can travel faster than the speed of light. Light moves as quickly as it does because it has zero mass. If you accelerate an object with a non-zero mass, its mass increases exponentially as you get closer to the speed of light, essentially prohibiting it from ever reaching the speed of light. However, if the mass is zero, then you can circumvent that issue and reach the speed of light.
——So does that mean that in order to surpass the speed of light, at the very least you need reduce your own mass below zero?
Prof. Futamase: With our current understanding, that's not believed to be possible, but that may change since it hasn't yet been proved impossible.
——I see. The "physical space" option sounds a bit like the Room of Spirit & Time.
Prof. Futamase: In the real world, it's theorized that we could create a sort of tunnel to the past. There are currently people researching what type of energy would be necessary for that to be possible.
——On a related note, what type of fuel do you think would be required to power a time machine?
Prof. Futamase: Our understanding today is built on the assumption that you would have positive mass. However, research has already shown that matter with negative mass also exists. So you could cancel out your positive mass with this "negative matter" to reduce your overall mass to zero, then potentially even pass through solid walls moving at the speed of light.
——So the fuel would have "negative mass". That's a little hard to wrap your head around...
Prof. Futamase: It's actually not that far-fetched a concept—there are already numerous discussions being had about its existence. It's thought that around 70% of the universe is made up of negative matter, which permeates it in its entirety and is the driving force behind the universe expanding at a speed greater than the speed of light, which is something that astronomers and physicists acknowledge as fact.
If we learn how to manipulate negative matter, it'll surely have a huge impact on all our lives and may be exactly what we need to unlock the ability to travel to and from the past and future.
——But how do we get to that point?
Prof. Futamase: That's exactly what we're trying to get to the bottom of now. It's like how in the past, we weren't able to extract oil from the ground, but as our civilization advanced, we became able to do so, and were also able to burn that oil and harness its energy. So I don't think it's unrealistic to think we'll be able to take the same leaps with negative matter.
——Woah! Now you've got me excited for the future!
Now that we've all hopefully got at least a vague understanding of how time machines could work, I decided to ask about parallel worlds and time paradoxes. Time paradoxes occur when some kind of contradiction or loop is created due to your travels to and from the past and future, and in order to enable time travel, we'd have to find a way to resolve them.
Even within Dragon Ball, Trunks altered his universe's history slightly by going back to the past to discover the Androids' weakness. It's this process that gives rise to multiple futures, i.e., parallel worlds.
——Could you tell me a bit about the latest parallel-world research?
Prof. Futamase: The concept of parallel worlds originates from the study of quantum mechanics. It says that at this moment, there are infinite universes that exist, and each one of them contains one 'you'. So if there were, say, 10 universes, then you'd simultaneously exist in all of them.
Simply by cognizing, "I'm here", the universe around you manifests. This is what's known as the many-worlds interpretation.
——So you're saying that there are multiple universes and that the universe in which you assert, "I'm here!", becomes fixed as 'your universe'...?!
Prof. Futamase: We're living in a reality built on the multitude of universes that are constantly being spawned with every decision we make. Assuming you travelled to the past, you wouldn't be in the past of this universe, which is the result of the accumulation of decisions made by its inhabitants, but a completely different one—in other words, a parallel universe. That reasoning allows us to resolve the paradoxes that accompany time machines.
——So in Dragon Ball, the future where the Androids run rampant and the one where they're defeated are actually completely separate universes?
Prof. Futamase: That's right. If you successfully travelled to the past then attempted to return back to the point in time you started from, the universe you arrive to would not be your original one, but a parallel world where you had travelled to the past. You'd essentially be in a new universe with a different history.
——So just to clarify, even if you never step foot in a time machine, the decisions you make from moment-to-moment spawn new universes...?!
Prof. Futamase: Precisely.
——Listening to everything you've spoken about so far, I thought of something else I'd like to ask you about. After his battle with Frieza, Goku travels to Planet Yardrat, where he learns how to use Instant Transmission. I have a feeling that Instant Transmission works in a similar way to a time machine, but what do you think?
Prof. Futamase: It's exactly the same. If you interpret Instant Transmission as movement faster than the speed of light, then Planet Yardrat must've found a way to overcome the gravitational restraints.
——So Yardrat's civilization must be far more advanced than Earth's!
Prof. Futamase: There's a strong chance that they're successfully using negative matter. That's exactly the sort of planet that scientists like myself are hoping we'll be able to make contact with.
It's currently estimated that of the approximately 200,000,000,000 planets in the Milky Way, around half of them have water and an atmosphere similar to Earth's.
——There are that many...!
Prof. Futamase: However, it takes around three billion years for intelligent life to evolve. On Earth, for example, it took close to four billion years for human life to emerge. So if a given planet is younger than that, then we can't get our hopes up.
It's also worth noting that even the lowest estimates predict that there are one billion Earth-like planets in each galaxy. It seems inevitable that civilizations make advancements, and so it wouldn't be strange in the slightest for highly advanced ones to exist.
——It sure would be nice of beings from those advanced civilizations or from the future to pay us a visit.
Prof. Futamase: Even assuming there were one hundred million of such civilizations... if those one hundred million were spread across the galaxy, then the distance between each of them would be roughly 100~1000 light years. I suppose we can only conclude that a civilization capable of using Instant Transmission over that sort of distance hasn't yet emerged.
——So it's possible that they're making their way towards Earth at this very moment!
Prof. Futamase: Don't forget there's no guarantee that they're organic lifeforms like us. Instead, they could potentially exist as data-based lifeforms.
——So perhaps signals from aliens or beings from the future are all around us, it's just that we don't have the technology to detect them... It's hard not to get swept up in all the possibilities!
I asked Professor Futamase about time machines, parallel worlds, and time paradoxes, and our conversation just kept expanding from there.
Research into time machines is still ongoing, but so long as they're not proved impossible, there's still hope that one day we'll succeed in building one!
With research being conducted as we speak and the ever-present chance that we'll make contact with more advanced civilizations, who knows what surprises the future—and the past—hold!
This site includes machine-translated texts. Please be aware that you might find some unusual expressions that are difficult to understand.