Forum: Story Ideas

Far past do over has been done iirc, but has a far future do over been covered?

How would that qualify as a do over?

In my opinion, far past doesn't qualify either.

Do over as in a second chance at life. Can't say as I agree with either being a do over either, but it is the closest tag that fits.

Not really. Time travel implies transit with the original body intact. Not a death then brought back to life in the minds original body at an earlier time, or another one all together.
Time travel of the concious is implied in any do over, but so is the original death.

Thus if a person who is born in 1950 and moves in time in 1990 if they turn up prior to 1950 or later than 1990 it's time travel.

I agree.

The essence of a "Do-over" is the chance to relive a life, usually with all the memories and knowledge gained the first time, which can then be applied to enable the second chance to be much improved.

It isn't a "Do-over" unless it's already been done.

Given that time travel is at this point pure fantasy, anyone's interpretation of it is just as valid as the next persons is. As such, there is nothing there to agree or disagree about in the first place.

Backward time travel is pure fantasy at this point, but not forward. Time dilation can easily cause what amounts to 'forward' time travel (cf. the 'Twin Paradox').

Relativistic effects (your time dilation) the twin paradox is based upon, is still in the realm of science fiction. While those relativistic effects can be measured on the micro-scale, getting one or the other twin up to significant portions of C isn't happening anytime soon.
With application of fantasy/science fiction, it can make a good story now, but in no way one based upon current reality.

Well, there are other variables that could thrown into the mix. Particularly for Gen X and younger, assuming research in longevity/health-span turn up "significant" results.

Throw in the possible development of cryo-sleep and other more advanced sci-fi tech(such as a fusion powered craft that can reach significant fractions of the speed of light). And you could possibly have a Millenial alive in something like 2300AD die and get thrown back into their past self attending high school back in 2003.

Well, there are other variables that could thrown into the mix. Particularly for Gen X and younger, assuming research in longevity/health-span turn up "significant" results.

Throw in the possible development of cryo-sleep and other more advanced sci-fi tech(such as a fusion powered craft that can reach significant fractions of the speed of light). And you could possibly have a Millenial alive in something like 2300AD die and get thrown back into their past self attending high school back in 2003.

About anything is possible with copious use of artistic license. Your scenario seems to plug more of the logic holes though.

About anything is possible with copious use of artistic license. Your scenario seems to plug more of the logic holes though.

There is a treatment methodology in development that is aimed at cancer in general, but specifically targeting prostate cancer at this stage(I'm under the impression that it was an easier testing target for whatever reason). It's done great in mouse trails so far. (Doesn't mean it'll translate well to human trials, many drug candidates did well with mice, and nothing in humans)

But based on the specific approach being taken. There is no reason to expect it not to work, as they understand exactly how it works and why. Rather than just trying random things until something works. (They just don't know what else it might target in a human. They don't think it'll target anything else, but that's different from knowing.)

If the treatment works well in human trials, we could possibly have reliable cures for the most common forms of cancer in the next 5 to 10 years.

There are other treatments in the pipeline to help with the underlying causes of heart problems in the elderly, and generally clearing a lot of other accumulated inter/intra-cellular junk from the body which are now understood to be triggers for a whole slate of typically "age related" ailments.

Understanding of our "gut biome" is also increasingly at an amazingly quick rate, and I'm starting to suspect a number of medical issues that started emerging in ever increasing numbers after about 1950 are ultimately going to be linked back to the use of anti-biotics.

Which will be interesting to see how people like the Vaxers take that one. Yup, those anti-biotics may have saved you from death by pneumonia, but it also happened to kill off the symbiotic gut bacteria that were helping keep your brain chemistry stable and protecting you from manifesting symptoms of (for example only, not backed by any study that I recall) ADHD.

Getting back on the general topic though. I do think the first (modern) person to live to see 130 is alive today. I also strongly suspect that by the time I'd be 80, most 80 Year-olds will be in much the same physical condition they were in their 40's, if not better. (That doesn't mean I expect the first 130YO to be from my generation, it could be someone younger than mine, or older for that matter)

If we are not off this rock when 130 year life expectancy becomes norm, the resource wars that will be taking place will knock it back down, if not out.

If we are not off this rock when 130 year life expectancy becomes norm, the resource wars that will be taking place will knock it back down, if not out.

Funny thing about 100+ year healthy life expectancy is a 5 year ROI likely morphs into a 20 year one. That kind of shift in corporate thinking in particular could trigger huge changes in other (beneficial) ways.

We already have a reliable cure for many forms of cancer. I was a 'test' patient for one of them a long time ago, long enough that so far as my doctor knows, I'm the second longest living survivor of testicular carcinoma in the world.

The one I'm talking about involves no surgery, no poisons, and no genetic engineering(well, any that requires "tailoring" to the individual--As they're targeting certain specific "receptors" that to date have only been found in cancerous cells). And could potentially wipe out most forms of cancer in the body in the course of 2 or 3 injections.

You might still need a periodic "booster" every decade or so if you start showing elevated levels of certain markers indicating the cancer is back as the underlying cause triggers it yet again, but that should be about as involved as the treatment gets.

It's a bit more than an engineering problem. I am a materials and mechanical engineer. I know for a fact the science isn't there yet to produce a drive that is capable of significant fractions of C in a time frame usable for anything. The specific science in question is fusion to my mind. There simply isn't a great enough understanding of it to pass that onto us lowly engineers.

Time travel appears to be impossible.

If it were possible, moving backward in time would be just as feasible as moving forward in time.

Michael does present one of the more logical arguments for forward time travel. If it were possible to move at significant fractions of C, relativistic effects would move the traveler foward in time relative to the observer on earth. That I would consider pseudo time travel. In Einstein's universe, it's the only time travel scenario allowed.

There is however some ongoing theoretical work on retrocausality. A good primer on the subject is the following;

Quo Vadis Quantum Mechanics? Developments Of Quantum Mechanics In The 21st Century: ISBN 978-3540221883

That touches on the quantum subject. Be warned though. Anyone claiming to fully understand quantum mechanics or physics is either self deluded or full of shit. There is some suggestion that time travel in the quantum-verse is possible 'both ways'.

I don't claim to understand it all, but at this moment in time, true time travel either way for a person is still fantasy.

Edited for typos

In Einstein's universe, it's the only time travel scenario allowed.

But, AFAIK, there are valid solutions to form a closed path in spacetime round rapidly rotating (large) masses. This implies time travel, and Larry Niven explored this concept in his short story Rotating Cylinders and the Possibility of Global Causality Violation titled after the Tippler paper, available in his collection Convergent Series

Tipler cylinder is hypothetical. Hawkins and a few others proved it was impossible to build a machine from that hypothesis in a finite region while still satisfying the weak energy condition. Get around that problem and you'll have a Nobel in the bag.

ETA: Current science says no to time travel for humans in a practical sense. Then again, the current science in 500CE said the earth was flat. We don't know what we don't know. Tomorrow is another day.

That is why you shouldn't believe anyone who takes a firm stance on whether time travel is or is not possible.

But based on what we DO currently understand, travel through time (one way) into the future is possible, or at least plausible. All you need to do is reach significant fractions of the speed of light for time dilation to occur, or to stick yourself into some kind of Cryogenic Sleep.

That said, A form of time travel into what we'd objectively call "the past" may be allowed, even for humans, thanks to some implications of Quantum Mechanics.

"All you'd need to do" is be able to transition between dimensions until you found an alternate dimension where they currently were experiencing the era/time frame you were looking for. But in that case, you're not traveling into your past, but rather traveling to somebody else's present day.

As it stands though, I don't think anybody even has a working theory of how you might go about transmitting either "data" or matter between dimensions in a controlled manner as of yet. So while it's "an exotic possibility" the mechanism for how you would do so is still unknown.

So let's pretend that time travel is possible.

Ignoring the fact that most governments would immediately want total control over both the method and those capable of it, what would actually happen?

If it were possible, then it wouldn't be confined to a single person, such things never are, added to which human nature means nobody would leave things alone, some would try to effect change for altruistic reasons, others for simple greed. But therein lies the problem. Changing things has a ripple effect, with numerous people all changing things without any concerted plan... Chaos.

Not to mention the number of things that would cease almost immediately.

Stock Market

Insurance

Bookmakers

Lotteries

Elections

Law suits

Just knowing the future with absolute certainty would be enough to render those things pointless, but knowing the future can be 'tweaked' to benefit the 'tweaker'...

What does it take in materials and energy?

I would imagine that the requirements would be very high. High enough that only the very wealthiest would be able to attempt it.

What if it is possible to travel into the past, but because of how it works, it's effectively a one-way trip?

Even one person attempting to change the past (assuming that's possible) would be chaos, because the attempt would be governed by mathematical chaos.

On the other had is it possible to change the past at all.

There are a number of theories out there on this.

Many think that the attempt would simply spawn a new alternate time-line/reality leaving the original intact and unchanged.

One compares time to a river. Throw a rock in and you create a splash and ripples, but the splash ends and the ripples fade leaving the river unchanged. It takes a massive splash to permanently alter the course of the river.

My own thought on this is that the past may be technically mutable but is not mutable on a practical level. Why, because I can't accept the isolation of the time traveler from the change. That would require the isolation of not just the time traveler's present self, but his pre-time-travel self from the changes.

That is you can't change the past, not because it is set in stone, but because even assuming time travel is possible anything you might do in the past is already built into the present you know.

As to your list of consequences, and your final comment: It's not possible to know the present with such absolute certainty.

What does it take in materials and energy?

No idea.

I would imagine that the requirements would be very high. High enough that only the very wealthiest would be able to attempt it.

I imagine you are right. Then again, it could be that the costs are $250 and being in the right place at the right time. No DeLorean required.

What if it is possible to travel into the past, but because of how it works, it's effectively a one-way trip?

It wouldn't be a one-way trip, you could repeat and got back even further.

Even one person attempting to change the past (assuming that's possible) would be chaos, because the attempt would be governed by mathematical chaos.

Or governed by simple common sense.

On the other had is it possible to change the past at all.

There are a number of theories out there on this.

Many think that the attempt would simply spawn a new alternate time-line/reality leaving the original intact and unchanged.

If you went back and once there did or said or acted other than exactly as you did the first time, you would to a greater or lesser degree, change the past.

As for spawning anything, it is claimed god took seven days, why woulds anyone believe buying a different flavour of gum would instantly create an entire new alternate time-line/reality, one filled with everything that has occurred over millions of years, identical in every way, except you now have strawberry gum, not lemon. Really?

One compares time to a river. Throw a rock in and you create a splash and ripples, but the splash ends and the ripples fade leaving the river unchanged. It takes a massive splash to permanently alter the course of the river.

Throw a rock that sinks to the bottom, slightly diverts the flow, over time the bank erodes, the river changes course, bursts it';s banks, floods a city, kills thousands. It's not the size of the splash that's important, it's the size of the rock. :)

My own thought on this is that the past may be technically mutable but is not mutable on a practical level. Why, because I can't accept the isolation of the time traveler from the change. That would require the isolation of not just the time traveler's present self, but his pre-time-travel self from the changes.

That is you can't change the past, not because it is set in stone, but because even assuming time travel is possible anything you might do in the past is already built into the present you know.

Bottom line. It's all utter rubbish, yup, agreed.

As to your list of consequences, and your final comment: It's not possible to know the present with such absolute certainty.

It appears you mis-read my comment.

What I said was (my bold)

Just knowing the future with absolute certainty would be enough to render those things pointless, but knowing the future can be 'tweaked' to benefit the 'tweaker'...

It wouldn't be a one-way trip, you could repeat and got back even further.

That would just be two separate one-way trips.

The scenario as done in fiction/movies generally involves a large apparatus that sends a subject back in time, but the machine itself does not travel through time (other than the normal way). In this scenario the time traveler only has one, maybe two ways back to their original present. One, take the long way around :), and maybe, a per-arranged time/place for remote retrieval.

The scenario as done in fiction/movies

Are you suggesting that proves anything?

Impossible, even for a time traveler.

And you know this because..?

Well, there are theories of alternate realities/timelines where even without time travel, the timeline is constantly forking such that at every decision point, every possible choice is made.

Already covered that.

That would only be possible in a "Quantum Leap" type scenario where you are sending your "consciousness"/mind back into a younger version of yourself do-over style rather than a physical time travel scenario.

Again, you know that for certain because?

My point was that theories seem to be floated without the slightest consideration for the practicalities of the effect they would have, presumably because such consideration with make the theorist look silly. I really can't accept that anyone can claim a theory is correct and every other theory is therefore wrong, because they are all just theories, no tests, experiments, just theories, or if you prefer, "wild ass guesses". I have no more idea than anyone else if any of the theories are in the least bit possible. I do know that shining common sense and practicality upon them tends to destroy their credibility.

Impossible, even for a time traveler.

And you know this because..?

Because nothing, and I do mean nothing can be known with absolute certainty.

Because nothing, and I do mean nothing can be known with absolute certainty.

So, you are not certain of your name, date of birth, that 1+1=2, death, taxes... A great many things are absolutely certain.

So, you are not certain of your name, date of birth, that 1+1=2, death, taxes... A great many things are absolutely certain.

Certainty and absolute certainty are two different things. It's been many years since I've seen by birth certificate. Maybe I've been misspelling my name for years.

As for DOB, your birth certificate was created by humans and all humans are imperfect. It's not impossible that the date on it is actually wrong. Human memory is faulty. Assuming for the sake of argument that your BC is correct as to date/time of birth, when was the last time you actually looked at yours?

I have no memory of my birth. Almost no humans are capable of remembering their birth. So effectively, we weren't there to witness it, so we in point of fact can not be absolutely certain about when it happened.

1+1=2 is more axiomatic than factual. It is taken on faith, not something that is known as provable. Certainty doesn't really apply to it.

https://www.vocabulary.com/dictionary/axiom

While everything that lives dies (axiom, not provable), the date/time/place/manner of any individual organism's death can not be known with 100% certainty.

Again, with taxes, At that level of abstraction, you are dealing with axiomatic things that can not be proven and matters of faith, not certain knowledge.

If you get into specifics of how much tax you pay, particularly if you include all taxes (sales taxes in particular), certainty is lost rather quickly.

Ok, so you've established that you're not absolutely certain that you were born.

Not sure how that advances anything, but that seldom stops threads wandering in obtuse directions.

It is however a subject awash with Scientific Hypotheticals Ideas Theories

Ok, so you've established that you're not absolutely certain that you were born.

I am reasonably certain that the uncertainty in the fact of my birth is small, but no, I can not be certain that the uncertainty is zero.

If you get down to it, we can not be certain of even our existence. I take my existence as axiomatic. It is a matter of faith, not knowledge, to which certainty does not and can not apply.

As for DOB, your birth certificate was created by humans and all humans are imperfect. It's not impossible that the date on it is actually wrong. Human memory is faulty. Assuming for the sake of argument that your BC is correct as to date/time of birth, when was the last time you actually looked at yours?

There actually was a case that got some limited national attention(CBS News) involving a guy DNA testing at a genealogy site and ultimately finding out he was born on December 8th, 1941 rather than December 7th, 1941. He also discovered the name was using actually belonged to somebody else, who had been living (and died) under his actual birth name. Switched at birth makes for complicated situations, particularly when you discover it 77 years later.

There actually was a case that got some limited national attention(CBS News) involving a guy DNA testing at a genealogy site and ultimately finding out he was born on December 8th, 1941 rather than December 7th, 1941. He also discovered the name was using actually belonged to somebody else, who had been living (and died) under his actual birth name. Switched at birth makes for complicated situations, particularly when you discover it 77 years later.

Yes, such situations are relatively rare, but the fact that they happen creates an uncertainty that is very small, but still greater than zero in everyone's DOB.

So, you are not certain of your name, date of birth, that 1+1=2, death, taxes... A great many things are absolutely certain.

I hear that in some circles 1 + 1 = 10

I hear that in some circles 1 + 1 = 10

Are you certain they are circles? They could be Hectogons.

I hear that in some circles 1 + 1 = 10

There's only 10 types of people in the world - those that understand binary and those that don't.

There's only 10 types of people in the world - those that understand binary and those that don't.

Sometimes.

Because nothing, and I do mean nothing can be known with absolute certainty.

Put down the box, and step away from the cat.

Put down the box, and step away from the cat.

Cat, what cat? This box is empty. :)

The scenario as done in fiction/movies

Are you suggesting that proves anything?

Nope.

That would only be possible in a "Quantum Leap" type scenario where you are sending your "consciousness"/mind back into a younger version of yourself do-over style rather than a physical time travel scenario.

Again, you know that for certain because?

Nothing can be known for certain.

That said, this is very simple logic. If you go back in time in body as your adult self, you are not/can not be in a position to make different choices for your younger self.

Perhaps by interacting with your younger self, that version of you might make different choices, but this is not predictable.

Your adult in body self doing something in the past through time travel is not a change to what your younger self did in your first pass through that time period.

If you go back in time in body as your adult self

But if you don't, if by going back you regress to your age at the time...

Just knowing the future with absolute certainty would be

Impossible, even for a time traveler.

As for spawning anything, it is claimed god took seven days

Well, there are theories of alternate realities/timelines where even without time travel, the timeline is constantly forking such that at every decision point, every possible choice is made.

If you went back and once there did or said or acted other than exactly as you did the first time, you would to a greater or lesser degree, change the past.

That would only be possible in a "Quantum Leap" type scenario where you are sending your "consciousness"/mind back into a younger version of yourself do-over style rather than a physical time travel scenario.

I tend to lean in that direction assuming time travel was possible, and if the time line didn't branch, then I'm not sure what would be the result. If the person who changed the past were to return to the future, they would see the differences. However, everyone living in the future time would have grown up with whatever resulted, they would have adapted to that whatever and to them it would be normal. Of course there are people who believe a timeline would heal itself, so to actually change a timeline, someone may have to change it several times to achieve a permanent change.

One thing I am curious about is, if timelines where to divide, would there be a limit on the number of timelines in existence; if so, what would happen if that limit were to be exceeded? Would two existing timelines merge or would one just end?

On the "energy conservation" standpoint, I'm going to assume either the energy required would be commensurate with the energy needed for "Creating" that alternate realm. (making it not very feasible, unless you go the infinite possibilities option, in which case energy requirements may be quite low) Or the realm was already existing, and they simply accessed it.

But going back to the "infinite possibilities" and assuming you do not actually travel backwards in time, but rather travel laterally between possible realms/dimensions, it is possible you could have any of the following (simplified) scenarios happen:

1) You start at Point A, travel to B and make changes, and return to A, nothing changed in your own timeline.

2) You start at Point A, teavel to B and make changes, and attempt to return to A, but instead end up at point C where "your changes" appear to have been made, but actually involved a different version of you.

2.A) Your changes may have prevented a "C" version of you from existing, but as you're not from C, that's "not a problem."

2.B) There is a "C" version of you, but they've since departed on an adventure of their own, presumably never to return, and you can simply assume their life oblivious to the fact you're not actually back in "A"

2.C) There is a "C" version of you, and they're still there.
2.D) The version of you that made the changes might not have left.

However, everyone living in the future time would have grown up with whatever resulted

Which would also include the time traveler.

That is one of the things about the theory of time travel. Prior to departing the traveler grew up with one history. If the traveler goes back and changes something that will affect the future, then if he retains his former memories when he returns things would be different than before he left. If things aren't different then changes in the past can't affect the future or the traveler's memories change.

Well, unless you go for the multiverse option, in which case you might have managed to return to your original timeline.

Which isn't the timeline you altered, so "of course" you wouldn't notice any changes. Doesn't mean a timeline failed to change, it just means you failed to change your timeline.

I do take a firm stance on it in regards to current known science and technology. Someone needs to produce a time machine to prove that wrong.

The key there is - current known

Agreed.

Also, most significant scientific breakthroughs are by people who do not accept the limitations placed on knowledge by those who say it can't be done due to the current knowledge levels.

Agreed. To a point.

There are two very different types of 'breakthrough' or 'discovery'.

Those things that exist already and are subsequently 'discovered'. Radar, for example. It wasn't invented, it already existed, used by bats etc for a very long time before Radar was 'discovered'.

To my knowledge nobody has 'invented' anything at all in space/time, rather they have simply begun to understand a little of how things happen, rarely why. The rest are just theories, increasingly built upon previous theories, very few are even remotely provable, to the point that much science 'theory' is more accurately science fiction.

Those things that exist already and are subsequently 'discovered'. Radar, for example. It wasn't invented, it already existed, used by bats etc for a very long time before Radar was 'discovered'.

Bats use sonar, not radar. Not the same thing at all.

Which I thought of just after hitting 'post', but then passed on an edit because I'd just been reading this as part of some research

Those things that exist already and are subsequently 'discovered'. Radar, for example. It wasn't invented, it already existed, used by bats etc for a very long time before Radar was 'discovered'.

Although RADAR's discovery is an amusing accident all the same. IIRC it involved some researchers near the US Naval Observatory near Washington D.C. who were testing a pair of radio transceivers passing messages between each other across the Potomac River when a ship passed in between them...

Although RADAR's discovery is an amusing accident all the same. IIRC it involved some researchers near the US Naval Observatory near Washington D.C. who were testing a pair of radio transceivers passing messages between each other across the Potomac River when a ship passed in between them...

First came Heinrich Hertz's 1887 experiments.

http://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture6/hertz/Hertz_exp.html

Hertz discovered that a conducting metal reflected radio waves.

Then there was Christian Hülsmeyer who patented the Telemobiloscope in 1903. This was the first application that could detect ships. However the ability to measure the distance wasn't there so some dispute calling it the first radar.

Leading up to WW2 work on a variety of Cavity Magnetrons (microwave producers) went on around the world. Leaders in that were the Brits, Germans, Americans, Japanese, and Russians in that order. The British version was instrumental in this when combined with the US monostatic application and timer.

The term radio detection and ranging (RADAR) was coined by the US in 1940. By this time, what is known as RADAR was active worldwide in several countries. The race to practical RADAR was won by the US, but it was not the first to its discovery.

It was the addition of a timing circuit that allowed the discernment of range. This was simply timing the initial pulse to return then dividing by 2 in a monostatic radar that won the race as first demonstrated aboard the USS New York early 1939.

The incident you refer to happened in 1922. By that time what is now known as RADAR had long since been discovered. At its root, it was Hertz. Without his work, the rest of it may never have happened.

Those things that exist already and are subsequently 'discovered'.

Just like my friend who went to the West Coast and "discovered" San Francisco.

ETA: Current science says no to time travel for humans in a practical sense. Then again, the current science in 500CE said the earth was flat. We don't know what we don't know. Tomorrow is another day.

False, the Ancient Greeks and Romans alike knew the earth was round and were actually quite close in their predictions as to the Earth's Circumference.

European scholars of the 15th Century also understood this. Columbus wasn't getting support for his expedition because most didn't believe his assertion of a much smaller global circumference, and knew there was no way to provision a ship to travel non-stop from Western Europe to China. Columbus was lucky enough to encounter a landmass before his supplies ran out.

True: Many of the days scientific minds were imprisoned, tortured, or outright killed for saying otherwise. The 15th century wasn't even commented on. 500CE (dark ages) is 1,000 years prior to the 15th century, so your're stating a false equivalency and practicing misdirection by even mentioning it.

It wasn't until much later in the middle ages and renaissance eras that it became the predominant belief, and even then it was argued.

The subject has been argued for the last 150 years by historians of all stripes. One thing both sides normally agree upon was that in the dark ages, the majority belief was for flat earth with few notable exceptions. Simply stating "False" is both exceptionally ill-considered at best, and down right rude at worse.

Columbus was lucky enough to encounter a landmass before his supplies ran out.

Actually, there is evidence that the Columbus might well have known that there was another land mass between Europe and Asia.

There is solid evidence that the Vikings reached North America as much as 2 centuries earlier than the Columbus Expedition.

I've also seen/read reports that there were earlier maps showing the Atlantic Coastline of South America built on reports from European Ships that got blown out into the deep Atlantic by storms, got close enough to see the coast but never landed, and managed to get back.

He likely spun a tail about a short cut to Asia and the silk road because he thought it would sell better to the then powers of Europe than tails of an unknown mystery continent.

Backward time travel is pure fantasy at this point,

Fantasy it may be, but one of the fun parts of a good time travel story is the mechanism used to accomplish the trip, whether it be a DeLorean (Back to the Future) or simply trying to replicate the surroundings that would have been there in the target year (Time and Again; target year 1882). The best part of the good stories is what I hope are realistic scenarios of everyday life in past times.

The 'Predictive Programming' theorists on Youtube think that Back to the Future II was one of the ways used by occultists to pre-announce the destruction of the Twin Towers. If real, someone was really having fun with the time paradox idea.

Therefore I believe past is unchangeable in regards to the same timeline, at least as long we fancy quick return to the later date.

I have a somewhat different take on this. We effectively can't change the past, not because the past is unchangeable in any physical sense, but because anything any putative time traveler does in the past is already built into the history we know. The time traveler can't separate his younger self from learning what ever history he creates.

I'm not interested in writing them, but there are two time-travel plots I'd be interested in reading.

1. Timed traveler goes back to stop some event only to discover that his own efforts to prevent the event actually caused it in the first place.

2. MC invent's/builds/uses time machine because he found either an early 19th century photo of himself or an even older painting of himself.

1. Timed traveler goes back to stop some event only to discover that his own efforts to prevent the event actually caused it in the first place.

2. MC invent's/builds/uses time machine because he found either an early 19th century photo of himself or an even older painting of himself.

Yes, both of those are paradoxical scenarios allowed to happen. Actually the only thing the time traveler can't do, is to remove reason for his visit.

So, if traveler goes into past to prevent a thing X, he can cause that very thing, or accidentally cast whatever other changes, but traveler can't prevent the thing X from happening, or else there was no motive for traveling in the past. If he did prevent X, then his future self wouldn't know it happened and wouldn't travel into past to prevent it. Therefore, it couldn't be prevented, what is a contradiction.

We both are saying almost the same, just from different viewpoints. Time traveler can't change their own history, or they memories has to change as well. Traveler may possibly change things, but only if they have no idea about those. What isn't particularly productive or sexy.

If he did prevent X, then his future self wouldn't know it happened and wouldn't travel into past to prevent it. Therefore, it couldn't be prevented, what is a contradiction.

Your missing the extent of the paradox in my described plot. The only reason x happened in the first place is because the time traveler tried to prevent x from happening. If he hadn't gone back in time to stop x, x would not have happened.

He created his own motive for time travel before he even thought of time travel.

Mind Blown.

No, I didn't miss the extent of the paradox.

In both scenarios you proposed it is classic time-loop, circular causality that exists because it exists. There's no reason for that not to be allowed, even if it is, well, paradox. Almost every time travel story contains one, just because it's fun.

Larry Niven, All the myriad ways

Back to the original topic, the closest story I can think of for this is David Gerrold's The Man Who Folded Himself

Niven's take on TT which can affect the past, is that if such TT is possible in a universe, then consequences of changes made will ensure that TT is not discovered in that universe (such as in Rotating Cylinders... mentioned above)