In the future, when an object emerges in a different time, that moment is referred to as a crowning. An impacted crowning is when said object materializes within another object, fusing with it. An aerial crowning occurs when it is a certain level above solid ground. I suppose we can also have aquatic crownings, for that matter...

This brings up a number of questions:

  1. Would materials simply fuse together, or would the forced merging of two materials set of some type of atomic explosion?

  2. Air itself is matter - Then why does the "fusing" effect not take place with a solid material and air?

  3. In order to mitigate the fusing phenomenon, all crowning events, by their nature, are preceded by what is known as "displacement." Meaning, that all existing matter is either vaporized, or simply "ceases to be" and is replaced by the emerging object. This either occurs by design (i.e. a pre-singularity is created in order to clear/swallow-up a certain area, so that it can be "made ready" for the object to have a clean entry, or it simply occurs via the laws of nature. Please explain the workings of either approach.

  4. As the problem of undesirable terrain/conditions is inevitable when doing any type of time traveling, does it not become a necessity to send a probe to do a quick check regarding conditions prior to sending the actual payload? What are some considerations of the "scouting" aspect of time-travel? i.e. you don't want to travel in time, only to discover that you end up in a pool of lava, or if you follow the John Titor model, you don't want to end up on an Earth which has so far deviated from the Earth that you know, and the atmosphere on it is completely different to the one you're used to.

  • $\begingroup$ Is the assumption that objects travelling in time do not travel through the intervening time? That time travel, in this case, is like teleportation, moving from point A on the time axis to point B without travelling through any of the intervening points? $\endgroup$ – jdunlop Aug 7 '17 at 6:16
  • 3
    $\begingroup$ The answer is probably "it'll do whatever you want it to do", then, because there's no way (in our universe) for an object to travel a distance along any dimensional axis without covering some of the intervening ground. So there's no basis (physical or theoretical) for "appearing in the same space as existing matter". $\endgroup$ – jdunlop Aug 7 '17 at 6:44
  • 2
    $\begingroup$ How about the question of why a time traveler doesn't appear in outerspace as soon as they time-jump? After all the Earth is traveling around the sun at 30km/s and the solar system is moving around the center of the milkyway at 230km/s and the latter is moving at 600km/s relative to distance galaxies and so on. $\endgroup$ – AngelPray Aug 7 '17 at 6:47
  • 1
    $\begingroup$ Years ago before I stopped bothering with time travel bs I did a switch thing, a time machine would teleport whatever is in the place back into the future from which it came. To answer your questions you have to know a bit about nuclear physics/chemistry and the answer would take a while. I feel your question is too broad that it is worth the effort. Also point 4 is completely based on how you decide stuff works and where they travel. I know that going back 10 years right now won't place me in lava e.g. $\endgroup$ – Raditz_35 Aug 7 '17 at 7:28
  • 1
    $\begingroup$ It would be simpler to time travel in a vacuum. For example, somewhere off the planet in space. When the traveller arrives in the past or future, they won't fuse with any matter. It is only an assumption that time travellers would materialize inside whatever occupies the place where & when they arrive. The presence of matter may prevent materialization. If materialization fusing is a problem, do it in a vacuum. $\endgroup$ – a4android Aug 7 '17 at 8:04

Save Points

The idea came from a4android's comment:

You create specific points in time and space which we prepare for time travel : perfect vacuum, and we save the exact coordinates (both in time and space) so that travellers can go there.

Time travel would then only be travel to these spots.

You would then have to manage the usage of such spots, several time travelers can't use them at the same time. I would imagine some kind of infrastructure that continuously welcomes time travelers, being able to take care of a certain amount of travels.

This is extremely restrictive but solves a lot of problems.

  • $\begingroup$ What is "perfect vacuum"? How does one construct those spots in the past? $\endgroup$ – Raditz_35 Aug 7 '17 at 10:40
  • 1
    $\begingroup$ How does one construct these spots in the past? : well you can't, you'd be limited to the moment you are able to construct them. As I said I am aware this is extremely restrictive. $\endgroup$ – everyone Aug 7 '17 at 11:44
  • $\begingroup$ What is perfect vacuum ? Well a certain area entirely empty of particles. I am aware that we are not currently capable of making "perfect vacuum", but my guess is that if the civilization is capable of making time machines they can make close to perfect vacuum. Otherwise make these spots in space. You would probably need some kind of suit to survive the travel anyway. $\endgroup$ – everyone Aug 7 '17 at 11:47
  • $\begingroup$ I think this would make for a very interesting premise if you put it like that, exploring the practical applications of these time machines. I imagine that the scheduling of arrivals alone could lead to some very interesting encounters $\endgroup$ – Raditz_35 Aug 7 '17 at 11:57
  • 1
    $\begingroup$ You could end up with a world where you could go visit your dead grand-parents, but only a certain amount of times. And when you get there you meet up with your yet unborn great-grand-son that arrived 5 minutes before you. Fun stuffs.You'd also have to arrive with a predefined return date, so that they can send you back at an available spot.However, the past people can't know when or where there will be an availabe spot. Traveling in the future would be complicated too. $\endgroup$ – everyone Aug 7 '17 at 12:20

Pure information scouting

Concerning point 4: the "scouting" aspect of time-travel.

You couldn't send any physical kind of probe back in time to "scout" the destination because it would encounter the exact same problems you would have if you went there yourself (possibly fusion or explosion or displacement, whatever you choose).

To check the terrain before jumping in time, you would need a way to send and receive pure information. In Alex Scarrow's "Time Riders", they use Tachyons to communicate through time: a hypothetical particle that always moves faster than light.

I'm guessing this is the kind of thing you're looking for, some kind of sonar through time. The problem with this idea is that I have no idea how you get the information back. You send your signal to scan a certain time, but I don't see how you could get them to suddenly map out a physical instance and then come back to the time from which they left.

This also disregards the fact that you need to send a physical being afterwards. I'd argue that you'd try to "land/arrive" back in time but in space (where there is as little matter as possible) with a space ship to come back to earth. The scouting would be to check that you are going to space.

  • $\begingroup$ I was thinking something along the lines of a drone/levitating-sphere which makes the initial journey and while the portal is still open, it sends back signals. $\endgroup$ – Ebony Maw Aug 7 '17 at 14:20
  • $\begingroup$ But as you said this stills causes a lot of problems : sending the actual drone/levitating sphere: even interaction with air could destroy it, and you'd have no guarantees it would arrive safely. A possible outcome : you send it back in time, it explodes killing several people and changing the entire future. The people that would have sent it would'nt receive any information, and the whole future would be different. This raises other problems: how does a change in the past affect the future? completely re-write it ? another universe? $\endgroup$ – everyone Aug 8 '17 at 7:18


Clearly, if you can time travel, then you can "un-time-travel," in the event of an impacted or aerial crowning.

If an event goes awry, you build in safe-guards to retroactively move the event to a better location.

Over time, software learns how to better self-correct for this, with AIs that make these corrections fast enough that even outside observers wouldn't be aware of the events.


Another technique would be to send a tiny probe through first. If a drone-like object or a camera lens on a movable "stick" goes throw and scans the area ahead of your crown event, then it can determine with high precision whether anything in the subject area would represent a negative outcome. Then the transition can be moved to a safer location before larger objects (people) go through.

  • $\begingroup$ I'm not quite sure I agree with the idea that "if you can time travel, then you can un-time-travel,"retroactively stopping a time travel from happening is extremely complex : you need to go back in time in a way that won't change the future and still be able to send the necessary information in the future for them to stop the time travel: You'd end up with a time paradox very fast. $\endgroup$ – everyone Aug 8 '17 at 7:10
  • 1
    $\begingroup$ If a time travel was retroactively "un-time traveled" with a time travel, then the "un-time travel" would not have a reason to have taken place because the first time travel would never have happened. So this depends on how time travel works and deals with paradoxes. $\endgroup$ – everyone Aug 8 '17 at 7:14


The solution is for the matter which travels forward in time to switch places with an equal volume of matter that travels backwards in time. This also sidesteps the problem of leaving a vacuum at the site where I was when I leave my time.

It would make it easier to probe the destination time: send a block of ice and see what you get in return. A block of lava? A block of brontosaurus meat? A block of clove-scented island air?

Traveling with a bubble of air around me will also give me a chance to remedy some errors - I might materialize in a very dark, very small cave, with a small bubble shaped oval of stone appearing at my origin time. I can go back, or make another jump to a time when that boulder is not there, walk a few paces, and try again.


This answer could easily be 100 pages long explaining everything, but I will just name some points you should consider. I will pretend that nuclei have an actual position in space because I think it is a good approximation in this context. I will also only discuss the first two points because I think they are plenty already. How people do time travel in your world is in my opinion whatever you believe is best.

Assume you teleport one solid onto another:

  1. Nuclei are very small compared to atoms. Very few nuclei will be teleported directly onto each other. Your main concern isn't some nuclear fusion / "atomic explosion" type of stuff.

  2. The actual problem is a chemical one. Usually, a material is in what one would call an equilibrium structure. Now you introduce a lot of new nuclei in different positions, resulting in something that no longer is at equilibrium. Let's not worry about conservation of energy/momentum because time travel and a magical machine that does stuff and focus instead on what happens next. Your "former material" desires to be in equilibrium, therefor a violent chemical reaction occurs - I do not even know what to compare this to. The material will almost certainly violently expand (because too many particles occupy too little space currently), it will radiate a lot (because we are dealing with a vibrationally excited state here) and all kinds of weird stuff. I'm even afraid to call anything specific, I suspect some beta radiation ( emitted electrons) for example - this is highly exotic. One definition of temperature involves the amount of molecules in a certain excited state. Since every "molecule" would be in an excited state, you would have (minus(?)) infinite Kelvin for a short while. Of course not an actual infinity because temperature doesn't make sense at one point anymore, but there you go. Does that make sense to you? It doesn't to me. I might be wrong about specifics here, but I think it is clear that nothing would survive this "crowning" time jump. Please be aware that the ultimate result of course would depend on what exactly is crowned.

If you now teleport on something less dense, the same will happen but to a lesser degree of course.

Also, just to be clear, if you were to teleport nuclei onto each other, all would be much, much worse. My above scenario wouldn't destroy earth or anything, just your time machine and lab.


You're kind of trying to solve a problem that you're introducing yourself here. The type of thing that I would imagine that you could find in any Sci-Fi technology (and Magic to a lesser extent).

The point is, take any technology which exists in Sci-Fi - teleporters, faster than light space ships, light-sabres, universal translators, replicators, androids, and if you analyse it close enough, you can find lots wrong with the concept, lots of points similar to the one you just made, and the only "real" answer is, "Yeah but that's why they don't exist in real life".

And the in-universe version of that answer : The inventors have encountered that problem and found a way around it. (So don't worry about it)

Now, I know that doesn't answer your question, so what I can offer is as follows: If you're considering a problem at that low a level you must also describe the process at that low a level.

You have a time machine that teleports the subject through time á la Back To The Future. How is the data sent back in time? As in what are the mechanics/details of the transport? Is it through a worm-hole type thing or a sort of hyperspace/4th dimension concept? Is there a transmitter/receiver & data transfer? Do they travel back as a tachyon wave and somehow rematerialise at the right point in time? Once you fleshed that out, what happens during re-entry, or "crowning", will be a lot clearer.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.