How far could we actually go into the future using relativity?

I’ve just read in my book* that Russian cosmonaut Sergai Avdeyev holds the record for traveling into the future, after orbiting for 748 days and being hurled 0.02 seconds into the future.
Given, say, 20 years, a heap of cash and political will, how far could we send someone into the future, and what’s the best way to do it, if we were running missions specifically to break that record?
*“Physics of the Impossible” by Michio Kaku

Approaching the event horizon of black hole and then accelerating to a significant fraction of the speed of light to escape would get you close to the heat death end state of the universe with a very minimal passage of time from your frame of reference.

Significant barriers to implementing this plan and it would require new physics to do so as chemical rockets are not fast enough but the only practical technology to accelerate with a large object that we know of today.

While you will never be able to reach light speed it may be helpful to realize that photons and other particles that are traveling at that speed do not experience time at all. Even the photons from the cosmic background radiation that reach earth, which from our perspective will have been traveling for billions of years would view their emission and absorption as a single event from their frame of reference.

There are no black holes we can reach within 20 years, nor can we count on new physics being discovered in that time frame. The only realistic option is to go as fast as possible. A one-way trip would get the most effect, but you may have trouble getting volunteers to give up their life to travel a few seconds into the future.

I wonder if anything reasonable could be done on the surface of the earth, avoiding all those pesky problems of space travel. Like a giant hyperloop circling the equator. How fast could we reasonably go without leaving the earth?

The problem with a hyperloop solution is all the energy you would be wasting maintaining a loop in opposition of the natural tendency to travel in a straight line. You’d be better off expending that energy accelerating towards a deep gravity well and then using the well to slingshot you back to your origin. Maybe a loop between Jupiter and Saturn if you want to stay within the Sol system. Or between Jupiter and Sol if you have adequate shielding.

The reality is that right now from what we know we will always be limited to pretty slow travel, so all of this becomes academic.

There is a huge problem with blue shifting of light when approaching the speed of light which would cause problems with our human bodies and gamma radiation even if we could make engines go that fast.

Get close enough to the speed of light and that nice space heater will appear to be emitting x-rays as you approach it.

I think it needs to be mentioned that relativistic time slowing isn’t “time travel” in the normal sense. You can’t get to a future that hasn’t happened yet for everyone else.

It does get weird when your future is someone else’s past though.

There is a fun little gem around free-will that seems to bother a lot of people trying to grasp the Einsteinian view. But yes in relativistic contexts your world-line already exists and the curious thing is that we experience time in a temporal way.

That pesky arrow of time and the propper clock ruin all the fun.

I"ve heard before that someone in the event horizon of a black hole could see the heat death of the universe, but what % of the speed of light do you need to attain to pull that off?

Also can you offer more info about your photon comment? I’ve never heard that before. Do they experience their entire existence all at once?

From what we know right now if you are in the event horizon it is too late.

This subject becomes complicated but from your own personal clock you may never reach the singularity in some forms of a black hole. Some types of black holes would spaghetti you before you get to that point.

If we could see an object falling radially into a non-charged non-spinning black hole to an outside observer they would just stop at the event horizon. The problem being that any light would be redshifted so you couldn’t see them anyway but they would just stop for a time than is greater than the heat death.

The person falling wouldn’t notice this BTW.

The trick without fallinging is to get close to the event horizon of a super massive black hole but to not cross it. If you can reach escape velocity you will feel like you travel far into the future.

While this is still unsettled the main line of thought is that when you cross the event horizon radially out becomes the inaccessible dimension that is currently backwards in time. That flip in the in-accessible degree of freedom may allow you to access the past or the future but accessing it would hasten your decent to the singularity and there is a chance that the radiation would burn you up anyway.

It is a complex and fun mindbender but do realize this is all just guesses without any experimental proof and most of these thought experiments involve non-charged non-rotating black holes that would never exist due to properties like the conversation of angular momentum. Most are fully a result of the famous physics spherical cow.

The cheapest and probably safest way to have practical forward time travel is to just move to a higher altitude.

Each foot buys you ~90 billionths of a second over 79 year life span IIRC. That may not sound like a lot but compared to the fuel bill and the radiation issues with fast travel it ends up being a pretty sweet deal.

Well, yes, but the question is about what we can do now, not what we could do theoretically. We’ve already got measurable time shift, my question is, what’s the most we could do now?

I don’t think this is true. Even in movie time travel the people left behind still age while you are away. We are just dealing with different time speeds.

I think that’s pretty much the definition of ‘future’, whichever way you get there.

But the OP said something about “sending” someone into the future.
If time dilation is sending someone then you’re being sent into the future right now.

Or, if you were born before 1985, we could say 1985 sent you to 2018.

In Science Fiction, where FTL travel is pretty much a given, they usually ignore relativity altogether. It irritates me to read that our hero, who has been whizzed off planet via a convenient wormhole, can return to Earth and still find the same people they left behind.

Suppose they used a centrifuge, the type that’s used for training astronauts for G-force. You know the thing I mean. How long would someone have to sit at, for example, 2G to beat the record?

If you don’t take advantage of the curvature of spacetime by moving up or down in a gravitational well, then the only thing the only thing that really matters is the speed you’re traveling at.

The Ames 20G centrifuge has a radius of 29 ft, which means that even at 2G, you’re only traveling around 30 mph. (The velocity of an object is circular motion is equal to √(a*r), where a is the acceleration experienced and r is the radius of the circle.) Someone who hopped on a Cessna for a similar amount of time would experience greater time-dilation effects.

The biggest shift achievable in 20 years? I’d be immensely surprised if it approached even 1 second. At the moment, the best we could hope for is sending somebody into orbit for long periods of time.

Dump enough money into it and maybe (just maybe) we can add some real delta-v and deeper space jogs if we have more than 20 years and extend this a bit. But not to the extent of hours or days. I’m talking a few seconds rather, which would be incredible on its own.

Significant time dilation effects require inordinate amounts of time or extreme velocities or gravity wells. Right now, we have to spend large amounts of time (with a tiny bit of gravity/velocity) to see a dilation effect. Getting to even 0.01c (1% of the speed of light) is a pipe dream with current or foreseeable tech.

It’s kind of like the difference between a million and a billion. They both sound big but achievable. But a million seconds is a few days. A billion seconds is a few decades.

Well, if time travel is travel, then you have to pass through all of the points between origin and destination - you can do this at 1 second per second, like we are doing currently, or at some greater rate (which would be time travel in a more common sense).

Fictional depictions of time travel often depict it as more like time-teleportation, where you get from origin to destination by jumping there directly, but (correct me if I am wrong) I don’t think the theoretical ‘real’ methods of time travel are purported to work in that way.

The closer one gets to the speed of light, the more time “slows down” locally in relation to everything else that is not moving at that speed. So, if you had propulsion technology good enough to reach, say 90% of the speed of light, for each day on board, two and a quarter days pass for an observer on earth with the respect to the ship in which you are traveling.

The rest is math. If you traveled for twenty years, you return home 45 years later on earth or, from your perspective, 25 years into what you would consider the “future” on earth. As Einstein would say, it’s all “relative”.

I’ve never explicitly bought an “around the world” plane ticket but multi-legged travels have taken me around the globe twice, both times counter-clockwise. Perhaps with better planning I’d have made one of these trips clockwise for balance, but I didn’t.

I don’t travel much anymore and it’s unlikely I’ll be able to unwind this imbalance once, let alone twice. So I am now permanently stuck two days in the future! :eek: (or is it two days in the past?) I don’t know if I have this to blame for any on-going psychiatric issues — but at least I get to celebrate my birthday twice a year! :slight_smile: