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Let's assume for a moment that we live within a simulation. Let's now assume that roughly 400k city (with inhabitants) and a couple of neighboring settlements gets removed from the simulation and then forked multiple times into smaller simulations. The original simulation gets thoroughly adjusted to remove most of the notions of existence of the city (maps, memory, books, contracts, etc.)

In one of the new simulations things continue to work as before - whatever is necessary for functioning of the city continues to do so and the people living inside to move outside of the city (let's not get into details why). What I am curious about is at the level of physics: would it possible for the simulation owner (or maintainer) to adjust the properties of physics in some small, but measurable ways (e.g. make speed of light different). In other words, would it be possible for a traveler from the original simulation to the forked one to make observations and see discrepancies from what he expects to see? Since there are far fewer observers of the simulation, is it possible to make some changes? The expectations of having certain properties (e.g. some constants) get adjusted within the new simulation, so the remaining scientist see these as normal.

To clarify: the folks in simulation A have memory of law of physics A, the folks in simulation B have the memory of law of physics B. When a person from simulation A travels to simulation B (with the exception of the people that were transplanted initially), they retain the knowledge from their original simulation.

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  • $\begingroup$ It's not just time that's relative as some chap called Albert once remarked, time perception is equally variable. No one "notices" the speed of light, they measure it. The instruments used to measure it are equally subject to being altered in a simulation according to any standards you wish. $\endgroup$ May 31 at 5:13
  • $\begingroup$ @ARogueAnt. I guess I wasn't clear in my question: I don't want the simulation to be obviously a mismatch. Of course I could make every person green and say it's normal and the simulation works somehow. However, what I am trying to achieve is keep everything the same and have only slight changes that are still passable. For example changing the speed of light could potentially mean that light from some stars would not reach earth and the night sky would be different. That's a pretty obvious change. $\endgroup$
    – gruszczy
    May 31 at 15:00
  • $\begingroup$ That would only be very distant stars in galaxies far away. Halve the speed of light and the night sky will look just the same to the naked eye. You've not specified a tech level for the simulation's worlds. $\endgroup$ May 31 at 15:04
  • $\begingroup$ Technology level: From early 20th to early 21 century. $\endgroup$
    – gruszczy
    May 31 at 17:09
  • $\begingroup$ To add more: could pi or Planck's constant be different in a different simulation? I don't think pi could be, as this is just a value based on an abstract concept. But what about Planck's constant? And could it be just slightly adjusted? $\endgroup$
    – gruszczy
    May 31 at 17:54
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Not without killing the transplantee

Cells run on an insanely intricate and delicate biochemical balance. Mostly this runs on variations in the electromagnetic force. Gravity is too weak to have an effect (humans can survive in microgravity), nuclear forces are too strong to be disrupted. But tweaking the electromagnetic force, speed of light, or similar things will cause "problems". Changing c will adjust the width of electron-potential wells, changing the shape of molecules and causing proteins to misfold, at best. Changing other parameters will mess with what's biochemically-thermodynamically profitable in terms of energy release.

In other words, the cells of the sim-A resident will stop working when they visit sim-B.


(Oh, and messing with nuclear forces much can cause your victim to blow up as a fusion bomb, as if you'd compressed their atoms past stellar-core density. You may destroy the pseudo-Earth if you import someone whose physics are too different.)


Edit, based on OP's request:

The nuclear forces create stable atomic nuclei with a certain proton-neutron ratio. That doesn't affect much chemically as long as the nucleus is stable, but if you mess with those forces, then the title of "most stable isotope" moves around and the atoms undergo radioactive decay as they approach stability. Biology handles this like a building made of bricks which randomly explode, replicate, or turn to cheese/titanium/steam.

The electromagnetic force is covered above.

Changing c has other effects even is everything else is constant. Modern electronics are limited in speed mostly by how fast information can get from A to B - the data on one end of a wire is literally different from the data in the middle, let alone the other end. Think of it like trying to pick parcels off a moving train, only your train is now going half/twice as fast.

Adjusting gravity may cause: atmosphere loss/decompression, orbital changes (everyone dies), solar fusion stuttering (extinction event queued), tectonic shifts, and/or pancaking humans until their hearts can't supply blood "uphill".

Assuming that the simulators can and do adjust for all of this in the initial change, some minor changes to gravity or c are permissible/reasonable to not kill the traveller. Gravity will change atmospheric pressure, so tweaking c is a reasonable choice. But who measures c for fun more than once?

A reasonable limit would be to run the city and immediate surroundings in a micro-sim, and listen in to the "normal" sim for the surroundings (ex: starlight, atmospheric pressure). This lets you tinker more, since you don't have to worry about disrupting the Sun or accidental hyperbaric effects.

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  • $\begingroup$ Asimov's The Gods Themselves explores this, and how to do it relatively-safely. $\endgroup$
    – Anon
    Jun 2 at 3:16
  • $\begingroup$ Thanks a lot for the answer - this was actually what I was looking for. Can the natives of sim-B survive at all if something is changed? Or would their biology have to function differently in the new simulation? Thanks a lot for the answer BTW, this is what I was looking for. I don't want to nily-wily change things, because "simulation can be anything". I expected changes to physical rules would affect biology, so I am wondering if there is anything that could be changed and still have things function properly. Maybe I could adjust the gravity a little safely? $\endgroup$
    – gruszczy
    Jun 2 at 15:25
  • $\begingroup$ I'm afraid you're mostly limited to gravity if you don't want significant problems. Atomic (nuclear) stability is based on a balance between electrostatic repulsion and the nuclear forces. Changing that balance will make lighter/heavier isotopes of elements more stable, leading to a surge in radiation. (Although you could run a short script to clean up 99% of that.) As discussed, biology is highly sensitive to the electromagnetic force. Editing c will affect microelectronics (i.e. every CPU) at the least. And if sim-B includes orbital mechanics, survivable gravity is very constrained too. $\endgroup$
    – Anon
    Jun 3 at 3:19
  • $\begingroup$ Thanks a lot for all the information! $\endgroup$
    – gruszczy
    Jun 3 at 15:41
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Simulations can be anything

In our world we have a ton of simulations. Games, physic engines, weather predictions and many more are all working with simulations. The key point of a simulation is that it isn't the true thing at some level. Some are more blatant than others. The day-night cycle is simulated in many games, but it moves much quicker. The shadows are rendered with light maps or are pre-installed instead of ray tracing for example. The weather is based on the whims of a random seed generator. Even if you go the true way, like ray-tracing for shadows, you still simulate it.

There is no reason why the physics would break down in a simulation if you change a few things. $ 0.7C $ wouldn't change a thing. Shadows are calculated with pre-rendered light maps? No one might know, nor would it have any effect. Changing gravity, or the efficiency of mitochondria, the bounciness of rubber or the strength of titanium. Hell, you can even add or remove whole molecules, allowing unobtanium but no gold.

We might be in a simulation already. If the light is rendered a different way, without moving through space, how can you know? They can simulate it it arrives when it should arrive. If you look through a microscope, how are you sure the bacteria aren't only now rendered as if they were always there? How can you know your body isn't just a set of simple parameters, getting only more complex when the inside is revealed though surgery or scanning techniques? Earth might truly be flat, there is nothing beyond the water for Truman, the sun is a painting in the sky, the food is just simulated to appear in the giant warehouse and delivered by digital projections to the shops, the gravity doesn't exist and the whole thing just accelerates through space, resetting it's speed every so often.

There is no reason we can know some things. The simulation can be convincing and lifelike without any of the correct ways to create it. You can change things as well, where many are difficult or impossible to notice, unless you're actively looking for it. A $ 0.5C $ is likely unnoticeable unless you start measuring, at which point the simulation could speed up the light in that single room.

The simulation can be anything you want and do what you want. You can potentially change everything while the result is the same. So to answer your question, everything can be changed. If you change it in a way they can barely notice, you can still change all of physics.

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    $\begingroup$ Aaah, Physic engines: For when you need to simulate medieval medicine. :-D $\endgroup$
    – Joe Bloggs
    May 31 at 16:36
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The Short answer is Yes

You have specifically stated that the changes will be measurable and the example you gave was "change the speed of light".

So all that would need to happen is you fork a person with the knowledge and capability of resuming the speed of light ($ C $) and he realises that it's now $ 0.75C $ and then the person has just realised something is not right.

This may or may not lead to them going "does this mean I'm in a simulation" but changing something that fundamental will raise some serious problems anyway.

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  • $\begingroup$ I would be more interested what could be safely changed from the simulation perspective. In the original simulation constants must have been chosen for a reason - would it be possible for the requirements to be different in a reduced simulation? $\endgroup$
    – gruszczy
    May 31 at 4:52
  • $\begingroup$ It seemed to cover the question, so I upvoted. Based on the comment of @gruszczy I added my own answer. $\endgroup$
    – Trioxidane
    May 31 at 7:05
  • $\begingroup$ @Trioxidane I think I am looking for something else, but perhaps I am not clear enough. For example, everything being equal and just changing the speed of light from C to 0.75C wouldn't that mean that the sky at night could be potentially different? Are there perhaps some stars that would reach earth with 1C, but not 0.75C? $\endgroup$
    – gruszczy
    May 31 at 14:57
  • $\begingroup$ @gruszczy they can be different, but this is a simulation. You can decide that stars reach it nonetheless, the colour doesn't change and the like. You're master of the simulation. The simulation has to follow a set of rules, but you can change them or add in exceptions. Mind you, these can also be accidentally found. $\endgroup$
    – Trioxidane
    May 31 at 15:06
  • $\begingroup$ @gruszczy if you only change the value of $ C $ (assuming our current value is the Universal Constant) you're correct, the night sky would look radically different with stars not there, and others "still" there that have already disappeared. Trioxdane is correct though, you can just handwave that the sky stays the same for reasons $\endgroup$
    – Joshua
    May 31 at 21:27
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If your people are in a simulation, what they observe and what they remember is also dictated by the simulation.

If the simulation makes them remember that the speed of light is pink elephant only on Thursday but pumpkin latte every other day, so it will be. And if there is no line of the simulation that make them wonder about how incongruent that is, they will carry on like nothing has happened.

Same applies for validity of physical laws. If the simulation dictates that the right hand rule applies only in continental Europe while in UK the left hand rule has to be followed, for them it will be perfectly normal.

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  • $\begingroup$ I add a clarification. Post city transfer the travelers retain their memories. $\endgroup$
    – gruszczy
    May 31 at 4:43
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Well the issue, in the absence of magic for exmaple existing in these simulations, minor adjustments to what you described would have profound effects on living organism and ecologies.

Life evolves to very specific constraints as we've noticed by the earths example.

If you are suggesting a simulation, you could just slow time :P You're also saying a simulation so sure you could adjust ambient temperature speed of light gravity etc, and your simulated people would die.

So, if the outcome is you're ok with the people dying, sure.

Otherwise, no. unless by EXTREMELY INFINITESMALLY SMALL amounts.

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  • $\begingroup$ I think you are grasping what I am looking for: a simulation can be anything, and yet the main simulation behaves in a certain way and we suspect reasons for that (e.g. speed of transfer of information, biological processes). What can I change that would not affect the life as it is, but still be measurable and "weird"? $\endgroup$
    – gruszczy
    May 31 at 17:11

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