This question is somewhat inspired by the number of "time bubble" questions that have been popping up on the site recently. If a real "time bubble" with a large enough time distortion factor existed, entering or leaving the bubble would mean certain death, as parts of the body on the fast side of the bubble edge would die of blood loss while the heart was on the slow side, and when the heart enters the fast side, vessels on the slow side would burst due to overpressure. Of course, if other factors affect the survival of a person crossing a bubble barrier, please address those in your answer.

The question, then, is: What is the maximum time distortion factor that is survivable by a normal, healthy person for the time it would take for a person to fully cross the boundary at walking speed. Of course, legal limits in a world with such time bubbles would probably be far lower than this, to account for accidents or those with weaker hearts or other health problems, but the purpose of this question is to get a sense for the absolute maximum.

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    $\begingroup$ This is going to be a hard one to answer, as there are a lot of fundamental questions that need to be answered about how the time bubble boundary affects things. One such question is how a liquid behaves when there's a time bubble boundary in the middle of it, but that requires answering how electromagnetic forces are affected by the boundary. $\endgroup$
    – Rob Watts
    Commented Jul 20, 2018 at 17:30
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    $\begingroup$ More fundamentally, what happens as a single molecule passes through the boundary? Going from slow to fast, as the first few atoms pass through they now are trying to move twice as fast as they had been while the other atoms in the molecule are not yet moving that fast. Even going from 1x to 2x might be enough to cause a significant fraction of the molecules in your body to tear themselves apart. $\endgroup$
    – Rob Watts
    Commented Jul 20, 2018 at 17:44
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    $\begingroup$ In that case, I will only point out that...depending on the engineering constraints of this technology (assuming it's a technology)...one could possibly get humans to be able to cross a larger time distortion factor by having multiple concentric bubbles, each of which steps up the distortion factor by another increment. This would approximate a smoother gradient, and presumably decrease whatever difficulties a person would have in crossing it. Kind of like an on-ramp to a highway. $\endgroup$
    – Qami
    Commented Jul 20, 2018 at 17:51
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    $\begingroup$ @Qami, yes that would probably be what would happen. However, each time-field generator would probably have a cost, so the greater the possible distortion-effect, the less the total cost of a given bubble. Therefore, to maximize efficiencies each of the bubble-barriers would probably distort time as much as possible. Hence the question. $\endgroup$
    – Gryphon
    Commented Jul 20, 2018 at 17:59
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    $\begingroup$ I could imagine walking through a sequence of bubbles, each just a bit more dilated than the previous -- kind of like going up and down stairs. To continue the analogy, you might die if you dropped 100 feet all at once, but if you take those same stairs back down 5 inches at a time, it won't kill you. $\endgroup$
    – Xantix
    Commented Jul 20, 2018 at 23:49

2 Answers 2


Case A

Assumption #1: The transition from one perspective of time to another perspective of time is instantaneous. In other words, the walls of the bubble are infintely thin.

Assumption #2: Things happen more quickly inside the bubble than outside (time is "faster" by comparison).

In this case, as my body passes through the bubble, the chemical processes speed up. My metabolism shifts into high gear, but only for those portions of my body that have passed through the membrane. The flow of my blood does NOT speed up until my heart passes through, at which point it beats faster.

  • Cells are demanding nutrition and generating waste at a faster rate inside the bubble.

  • The muscles what have moved through the membrane want to contract/expand more quickly, but the nerve impulses from the brain aren't yet fast enough. This could lead to jerkiness or loss of control, like Parkinson's Disease, until the brain passes through.

  • Your blood pressure in the areas inside the bubble would be low. The greater the shift in time, the lower it would be because it's being pushed by the heart on the other side of the membrane. Remember, chemical reactions speed up, mechanical reactions speed up, but the heart is the mechanical reaction and it's not there yet. Thus, the blood decays faster, but it doesn't move faster. Once the heart moves across the boundary, there's a momentary (and probably painful) spike in blood pressure as it all equals out. At this point the blood in the part of the body outside the membrane is HIGH. I can easily imagine the later-parts of the body to experience broken blood vessels/capillaries (aka bruising) from the transition.

  • The bloodstream is loaded with yucky stuff that isn't passing to the liver and kidneys quickly enough.

  • As I pass through the membrane, septicemia sets in and cells begin to die for lack of oxygen, etc.

  • Most of the vital organs aren't compromised (for a moment, for example, the liver is processing at two different rates), but the heart and brain are. The brain doesn't have a physical manifestation (so to speak), so let's assume that it survives (though portions of it are "thinking faster" momentarily... for a sec you'd feel like a genius). But the heart... portions of the heart start beating at a different rate than the rest. Leading to cardiac arrest.

  • The pain would be... impressive... and you'd feel it fast. From disrupted nerves to dying cells, it would be the most painful experience in your life.

Case B

Assumption #1: The transition from one perspective of time to another perspective of time is instantaneous. In other words, the walls of the bubble are infintely thin.

Assumption #2: Things happen more slowly inside the bubble than outside (time is "slower" by comparison).

In this case, as y body passes through the bubble, the chemical processes slow down. My metabolism slows, but only for those portions that have passed through the membrane. My blood does NOT slow down until the heart passes, at which point it beats slower.

  • Cells are demanding less energy and muscles are moving more slowly (like after a stroke).

  • Way too much nutrition is coming through the bloodstream leading to hyperoxia and oxygen toxicity, possibly leading to seizures.

  • Most of the organs aren't compromised, as before, but your brain "acts slowly" as it passes through, making you temporarily feel dumb as a stump.

  • Your heart still goes into cardiac arrest. The blood pressure inside the bubble is HIGH until the heart passes through, then you pass out from the sudden drop in pressure. Leading body parts are bruised from the high pressure.

  • You wouldn't feel the pain as you entered (at least not quickly), but you'd feel it on the other side. Oh, yeah...

Case C

In this case, we change Assumption #1 such that there's a transition period. The "membrane" or surface of the bubble isn't infinitely thin, but some thickness that allows for a gradual transition from Time #1 to Time #2. Obviously, the thicker the membrane the easier the transition. Which suggests that with a thick enough membrane, almost any time shift can be permitted. The thinner it is, the less time shift can be tolerated.

Yeah... but what does all that mean?

There are a lot of variables that we're ignoring. Are you passing through feet-first? Then moving into a faster time would likely cause your nose to bleed after your heart passed through. Head first? You'd likely die of brain oxygen starvation before the heart got there, etc. There are a LOT of variables.

Your worst case is the infinitely thin membrane such that the shock is greatest. So, how much time could you withstand?

  • If your goal was to completely pass through the membrane, I believe a shift of almost nothing would kill you from cardiac arrest. If it didn't, you've have permanent neurological problems like Parkinson's Disease from the nerve damage. And that's assuming you didn't die from an aneurysm caused by the shifts in blood pressure. From my EE college days, 3% or less is generally considered "statistically zero" because everything is generally happening inside the variance of noise. But I'd bet having half the heart beating at a change of 3% speed would still cause a cardiac arrest. Therefore, assuming the infinitely thin membrane, I'm suggesting it can't be done (or can't be done for any useful shift in time. Microseconds might be survivable).

On the other hand, if you had something like a temporal decompression chamber where the body as a whole could be slowly adjusted to the new time stream...

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    $\begingroup$ That "temporal decompression chamber" is actually decently popular in hard sci-fi that uses time bubbles like this. I remember reading one story (though I can't for the life of me remember the name any more) where passengers travelled to distant planets or across great distances by walking about a hundred feet down a tunnel. At the center of the tunnel, time was almost completely stopped, and the sides were both gradually ramping up the time dilation. At the end, the person (and their 'stopped' time bubble) could be extracted and moved. All they experienced was a brief flicker and some nausea. $\endgroup$
    – anon
    Commented Jul 20, 2018 at 21:15
  • $\begingroup$ @NicHartley that was a fabulously clever idea! At any given moment your perception of time never changes. Thus, the walk really would feel like a quick stroll through a hall. Dang... I wish I'd thought of it first. $\endgroup$
    – JBH
    Commented Jul 20, 2018 at 21:17

"Put your hand on a hot stove for a minute and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute." - Albert Einstein

I'd say Einstein sets the lower limit for answers here. Any time-distortion effects which only cause a 1:3600 time difference would be less disruptive than spending time with a hot stove and a pretty girl, and we know they already exist. I cannot find any research exploring the distortion caused by a hot girl and a pretty stove, despite there being some extraordinary examples of the latter.

Practically speaking, the limitation of this question is that there is no one accepted mathematical model for a commercial grade time bubble unit. Nobody can say what happens. For example, if you go from a slow region to a fast region, do we need energy? If we do, we might have issues with boiling over on one side or the other.

If your mathematical model includes a pressure gradient created by atoms moving one way or another, the survivability line might be surprisingly low. As it turns out barotrauma is something that causes the human body a great deal of trouble. If the particular pressure gradients you run into cause the lung pressure to be just 10% higher than the pressure outside, that's enough to cause rupture. This effect would not be mediated by multiple bubbles. If the effects of the bubbles increase the pressure from the opening of your mouth down to the lungs, you'll see barotrauma issues no matter what clever math happened in between. (related: the eardrum bursts if the pressure behind the eardrum, managed by the Eustachian tube, and the pressure in front of the eardrum differ by 0.75psi)

If your model involves changing masses (E=mc2...) to keep the pressures the same, then a lot of chemical reactions will occur faster on one side or the other, so you're going to have to tweak a whole lot of constants to keep the body functioning on one side or the other. The exact health-and-wellbeing costs to such a model will be associated with the exact equations you use.

The best solution is to simply not cross the boundary. Approach these bubbles like Terminator did their time-travel bubbles. Keep your hands and feet inside the vehicle until the ride has come to a full and complete stop. If you build the bubble around someone rather than having them pass through it, many of the problems go away.


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