4
$\begingroup$

Assuming we have the technology to travel to the past (about 2 years ago for example). If I replace someone who is in a coma about to die of cancer with a clone (in this hypothetical situation, for ethical purposes, the brain was not developed and would be "programmed" to shut down the moment the individual dies.).

And bring this individual from the past to the present (observation: no one from the past would know about the exchange, family members would suffer the loss). Is this hypothetical situation possible? There would be no paradoxes because the past would not actually be being changed. Only something from the past would be carried into the future (assuming there is technology this person would be cured and would be "dead" in the past, but alive in the present future) Would there be any implications that prevent this situation, apart from the technological means to go back to the past?

PS: Sorry for my English ;)

$\endgroup$
2
  • 3
    $\begingroup$ This reminds me of the movie Millennium, where people from the future replace the passengers of airplanes that will crash, because they need to boost the population in the future. $\endgroup$
    – towr
    Jun 30 at 14:28
  • 3
    $\begingroup$ This seems entirely dependent upon the rules of time travel within your world. Keep in mind that things already travel to the future at a rate of 1 second per second. $\endgroup$
    – sphennings
    Jun 30 at 15:45

6 Answers 6

11
$\begingroup$

It depends

If you're okay with your world being only loosely based in reality, then yeah, sure. No one would notice, provided that the clone's brain is actually alive and they are just in some sort of induced coma. For the purposes of entertainment, it is not immersion-breaking to say that nothing changed.

Strictly speaking, no. Going back in time at all would alter the future. See A Sound of Thunder by Ray Bradbury. Every object you move changes the timing of future events, cascading into a different timeline. How did you get into the building? Moving a body isn't easy, and you probably can't teleport into the room itself. You'll have to blend in. But someone will see you, even if they have no suspicions. That changes their immediate thought process, and therefore the course of their train of thought for the rest of the day, or longer.

$\endgroup$
4
  • $\begingroup$ Thanks for the reply Ethan. But assuming if I have the technology to travel to the past, I could teleport to the room itself. in this hypothetical scenario, who knows, maybe even manipulate time, so that it manages to "slow down time", in relation to the observers. Assuming it was a perfect abduction (like a perfect crime with no apparent trace), in theory there wouldn't be any impediment right? $\endgroup$ Jun 29 at 21:49
  • 2
    $\begingroup$ @NatashaBarrosDelben I'll extend further Ethan's answer to the extreme limit : Even if you don't change anything to the exact atom and the dummy is identical to the person retrieved, the fact that you were in the room for a minute with two bodies instead of one also adds temporarily mass, mass which changes gravity forces in the whole universe. Sure, it shouldn't change much regarding believability (noone thinks about that, and it's normal how insignificant this is :p), but future is altered, very strictly speaking. $\endgroup$
    – Tortliena
    Jun 29 at 22:23
  • 3
    $\begingroup$ Regarding your point about "Going back in time at all would alter the future", what if traveling backwards through time was already a part of the timeline? Then traveling back should not change anything, as it already happened. $\endgroup$ Jun 30 at 8:40
  • 2
    $\begingroup$ @DoctorJones I assumed that wasn't the type of time travel logic that was being used because otherwise there wouldn't even be a need to ask the question. $\endgroup$ Jun 30 at 13:34
7
$\begingroup$

Not possible

There are two big problems:

  1. You cannot return to our present from our past

    You can go backward to a point in our history, but when you travel forward again, you'll end up in an alternate version of the present. Crucially: this does not depend on whether you effect some meaningful change while in the past. Probably, that alternate version of the present will be mostly the same as your original present, but it will be distinct, and that almost inevitably means it will already include a version of you that didn't travel backward in time. (Or maybe your parents never had you, in which case your existence is just a different kind of paradox.)

  2. Transporting matter from the present to the past violates conservation principles

    The problem with "paradox" is that it's usually much narrower than physics cares about. When a human refers to paradoxes, they are almost always referring to macroscopic events about which humans care, e.g. becoming one's own grandparent. But physics cares about balancing all the books, not just the ones we read, and it insists that the books be balanced every step of the way. This is just one reason that physicists have a dim view of time travel: it's practically impossible to avoid violating conservation principles because you're inverting cause and effect. It's not enough to just conceal your swap from the night nurse: you have to conceal it from all physical systems, which is to say that your trip through time cannot have any consequences whatsoever, including: you cannot absorb even one ray of light or one sound wave while you're swapping the bodies.


How do I justify the first statement?

Stephen Hawking's chronological protection conjecture states that the universe won't abide a paradox, and so if someone manages to violate the arrow of time, something else will always intervene to prevent a paradox. I then reason that since "paradox" is not merely limited to the kinds of events that humans usually care about, the universe's solution will necessarily be so broad that it can guarantee no paradoxes occur even at the quantum level. Stephen Baxter's novel The Time Ships is an excellent illustration of the regime I have in mind.

Reasonable people can disagree about how fictional time travel ought to work. This is the model I prefer when it comes to the realistic end of the spectrum. On the other end, where anything goes, the answer is trivially "yes": as long as you are super-sneaky when you're replacing bodies in the hospital, you can avoid a paradox. But you don't need to ask for our permission to play that way.

$\endgroup$
3
  • 2
    $\begingroup$ This is, strictly speaking, the correct answer. Even though the proposed use case for this time travel method (swapping bodies when nobody's looking) causes no obvious paradox, it 1) causes hidden paradoxes at the subatomic level and 2) could be used to cause much more obvious paradoxes like the grandfather paradox. Even if your particular plan were airtight, as long as the time travel method allows for paradoxes, it's inconsistent. Still, this story idea is dang close to paradox-free. If you like the concept, nobody but insufferable pedants will complain that you weren't rigorous enough. $\endgroup$ Jun 29 at 23:00
  • 2
    $\begingroup$ -1 This answer could be improved by explicitly outlining it's assumptions, before drawing conclusions from those assumptions. "You can go backward to a point in our history, but when you travel forward again, you'll end up in an alternate version of the present." is one worldbuilding choice (the assumption) (after all, as far as we know time travel is not possible), so answering the question by saying 'your assumption is not the same as my assumption, so what you're suggesting is not possible' is just... pointless. $\endgroup$ Jun 30 at 7:10
  • $\begingroup$ Regarding point 1, "You cannot return to our present from our past. We can get around this problem if the trip to the past was already part of the timeline. This trope has been used many times, and is widely accepted. $\endgroup$ Jun 30 at 8:47
3
$\begingroup$

Copy yes, original no

You'll need to drop "clone replacement" part in the past. Cloning would need to happen in present/future.

If we can somehow get an accurate snapshot of a moment in the past, it can potentially be recreated in future. But what's gone is gone - a person who died in the past would be dead for good, and what we would recreate is a clone of that person.

$\endgroup$
1
  • $\begingroup$ Thanks for the reply Alexander. Yes, I would take a clone from the future to the past and trade. and would bring the person just before dying from the past into the future. That is, she wouldn't even have really died, she would just have traveled to the future (as with astronauts, but on a much higher level), is there any theory that forces this individual to die in the future? Assuming that the future does not exist, and through our present we shape the future. $\endgroup$ Jun 29 at 21:55
2
$\begingroup$

Too few years may have passed

There was once a B-movie (unfortunately I don't remember the title) with a similar scenario. Agents from the future evacuated victims from disasters (e.g. plane crashes) before they died and exchanged them for cloned bodies they brought with them. Nothing changed for the grieving relatives in the present/past.

However, there it was about several centuries. With only two years journey into the future the problem would be that still the very most relatives would be there. They would be surprised if their mourned deceased relatives were suddenly there again. The exchange would be uncovered in such a way.

If that is not the story, I would recommend increasing the time gap significantly.

$\endgroup$
1
  • 2
    $\begingroup$ The movie Freejack has a similar plot: people from the future nab people from the past in the moment before their death. It's based on the novel "Immortality Inc" by Robert Sheckley, which I think has been adapted into movies or TV a couple of times. $\endgroup$
    – Tom
    Jun 29 at 22:57
0
$\begingroup$

may be

if you take time travel like in avengers endgame, then no.... in the avengers endgame. they time travel but that doesn't change the original events, although they make some changes in past events. yet they make it back to their original timeline. although they attempt to nullify effects by putting time displaced things back to their original timeline.

but in all other forms of time travel, where cause and effect are deeply linked. then not.

Also i suggest to use time inversion theory like in Tenet, this would be fun.. ๐Ÿ˜๐Ÿ˜๐Ÿ˜๐Ÿ˜

$\endgroup$
0
$\begingroup$

From a purely scientific perspective, consider what might happen if you put the person's body in stasis for that period. They would progress into the future at one second per second and arrive in the future with only a mild violation of entropy.

Next, you said "replacing the patient with a clone." This is, in fact, the plot line of Millenium by John Varley, except it's a far-future thing. I recommend reading that for an overview of the time travel considerations. Obviously, you're now talking about moving something back in time, which is scientifically impossible, but let's ignore that.

You'd have to make sure that all of the dental work was repeated, that scars were cut and fast-healed. Any squishy bits that were removed during the person's life, like appendixes and gall bladders, would have to also go. Depending on how much scrutiny the corpse would have to undergo, you'd also want to synthesize the ravages of disease: scarring of lungs and degradation of intestinal flora.

In Millenium, they got around this by only taking people from vehicles that vanished, or from air crashes where the bodies were too badly burned for little things like amputations to be noticed. I presume they didn't pull air crash victims from later years, when they could be identified by DNA.

But, yes, if you pull a body out of a spacetime and replace it with an identical body, you don't get any continuity issues. The only question is "how identical?"

$\endgroup$

Not the answer you're looking for? Browse other questions tagged .