Say, a person has a time conundrum. He thinks that some one has altered time and pushed the whole humanity back in time by several years, so he wants to conduct a simplest possible scientific experiment (he is rational, but not a scientist) to determine whether he is really living in the past.

Update : I'm not sure how could I be more clear with my question, I put it simple and crisp. If this was fact based question, I would have put in Physic. So I don't have anything more to make this question clearer, I request people who closed this question to reconsider. There are some great answers, I will update after reviewing the answers.


closed as unclear what you're asking by Wrzlprmft, T3 H40, evilscary, James, Ghanima Apr 22 '16 at 13:47

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 9
    $\begingroup$ We live in the present. $\endgroup$ – bowlturner Apr 20 '16 at 2:32
  • 1
    $\begingroup$ Call the Doctor? Is there any physical proof there used to exist a different future, such as a newspaper? Otherwise, based on our current technology, no. $\endgroup$ – Marion Apr 20 '16 at 2:45
  • $\begingroup$ For the second part, see this (which is similar). $\endgroup$ – PyRulez Apr 20 '16 at 4:59
  • 2
    $\begingroup$ What do you mean whole humanity? Only people? People and infrastructure? Farms and farm animals too? What about natural resources? Whole Earth? Whole solar system? $\endgroup$ – Euphoric Apr 20 '16 at 5:56
  • 1
    $\begingroup$ By "pushed the whole humanity back in time", do you just mean technological progress has been set back (so for example in the new timeline the industrial revolution doesn't happen until the 20th century), or do you mean what Euphoric and Thucydides are suggesting, that the world's population, cities, perhaps the whole planet, have actually been physically sent back in time to an earlier time period without them knowing about it? $\endgroup$ – Hypnosifl Apr 20 '16 at 23:21

The only way this can work is if the person sent back in time either has an amazing memory, or a photographic record of the position of the night sky.

The positions of the stars and the orbits of the planets work as a sort of long term celestial clock, and if you were to wake up one night and look out at the night sky and realize that the Moon, Jupiter or Venus were not in the "correct" positions, then you would realize that you are "out of time".

This is easiest to do if there is some sort of major astronomical event, such as a planetary conjunction (i.e. several planets appear close together in the night sky), a lunar or solar eclipse, or more rare, a comet.

OF course just because "you" know that the planetary conjunction you are looking at took place in year "x", "y" number of years before or after your arrival, sin't going to prove much. An astronomer can reasonably predict when certain astronomical events like eclipses and conjunctions take place and where in the night sky they are visible, so saying you are from 5 years in the future isn't going to cut it. IF you have an accurate picture of the night sky with a time stamp on your cell phone or camera, then you can make a stronger case, but since things can be Photoshopped, you will have a hard time proving your bona fides.

  • $\begingroup$ Pretty sure they used this method in an episode of Duck Tales where the nephews trick Uncle Scrooge into thinking it's Saturday instead of Friday so they can get their allowance a day early, causing world wide havoc. $\endgroup$ – Dark Hippo Apr 20 '16 at 11:11

You question is basically

How can I science that something scientifically impossible event has occurred?

You cannot. You cannot alter time, not within the framework of current science.

So you can't go looking for something, if you don't know what you are looking for. Given that science predicts that it is impossible, there is nothing to look for.

Further, as an observer within your history, how could you possible know? All your experiences will be from this "altered" timeline (otherwise, how did you come into existent in this timeline?).

Basically, without additional science, you cannot. Since this is your world, you can make whatever science you want.

  • $\begingroup$ Time travel into the 'future' is very much science fact. Whenever you move relative to someone elses frame of reference you are time travelling. Time travel into the past is admittedly harder, im not sure I would go as far to say it is impossible. Plausible methods exist (e.g. worm holes). $\endgroup$ – F_SO_K Apr 20 '16 at 20:51
  • $\begingroup$ Some solutions of Einstein's theory of general relativity would theoretically allow for travel into the past, like traversable wormholes or the Alcubierre drive, though it's suspected that when Einstein's theory is supplanted by a theory of "quantum gravity" this will turn out to be impossible. At least one physicist has speculated you'd end up in an altered past, see here. $\endgroup$ – Hypnosifl Apr 20 '16 at 23:26
  • $\begingroup$ @Hypnosifl You are merely confirming my answer. Each of your "solutions" requires more science. Wormholes requires topological changes to spacetime, for it to be traversable, you need strange matter. Alcubierre Drive requires strange matter plus energy equivilent to an entire galaxy, plus I know not of a solution to the Alcubierre Drive that allows for travel back in time. Quantum Gravity by definition is more science. I'm not saying that it is impossible, I am saying that current science says its impossible (the best part about science is that its wrong). $\endgroup$ – Aron Apr 21 '16 at 0:49
  • $\begingroup$ @Stu I'm not saying there are no Plausible methods, I'm saying that we can't say for certain how those methods work, given that they aren't science fact. $\endgroup$ – Aron Apr 21 '16 at 0:50
  • $\begingroup$ My point about quantum gravity was that it might not be possible in a future theory of q-grav, but if by "current science" you mean our current best theory of gravity, that would be general relativity, and backwards time travel certainly is theoretically possible in that theory. General relativity itself has no constraint limiting all energy to positive energy, it deals equally easily with positive or negative (and if you want to look at other 'current science', the Casimir effect in quantum electrodynamics does involve negative energy). And certainly it doesn't forbid enormous energies. $\endgroup$ – Hypnosifl Apr 21 '16 at 2:37

It depends on how far out time has been altered. The simplest way (assuming no access to the true present's star maps) would be to check universal expansion. If super novas are less red shifted then the universe has had less time to expand, meaning it's younger. As a bonus it would just be a single number to remember.


It might depend on how local (i.e. the frame of reference) the effect of your time travelling is. If the whole earth has been sent back in time relative to the solar system, the other planets in our solar system would probably be the best bet, they all move relative to one another in a predictable way and they are mainly highly visible (no specialist kit required). If the whole solar system has been sent back in time (relative to the Milky Way) you might be struggling, he could spot a super nova or other documented event in our galaxy, but he's probably going to need to be into his science to do that. That said super nova can be visible with the naked eye so as long as he knows where to look he could work it out.


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