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If we reflected lasers back to earth from mars could we receive information before the information is sent? If the information travelled at the speed of light to mars and back to earth would it effectively be time travel for information?

The most basic purpose of life, any life on any planet, is to reproduce. I can see generational starships spreading a race through an area of our galaxy, or even probes that deliver embryonic life to other star systems, but what is the purpose of your Von Neumann probes ? They can't gather and return information to the sender, as that would take twice as long as the journey to get here. So why would any advanced civilization undertake such a project that may return information outdated by millennia, or not return any at all. For any civilization to advance to a level of interstellar travel, they would need to use concepts like effort/benefit analysis, otherwise they would have made stupid decisions, and not advanced to such a level. And sorry, but sending probes that don't return information, or return it 10 000 years out of date, seems like a stupid undertaking to me. The second part of your post reminds me of the time travel problem ... "Time travel is impossible because no one, from a future where they have time travel, has ever been seen." For all you know, your UAPs might be from the future, instead of from other star systems; how would you differentiate between the two ? And why do you consider one choice more likely than the other ?

Radio works at the speed of light. Lasers are also already used for some communication. No time travel involved. Edit: my comment above was posted before the message above was seen. What do you mean by "binary light frequency"? And, it's still not clear why you think/thought information would be received before it is sent.

What is it in your scenario is it that makes you believe information might be 'time traveling'? Is it because you use lasers? Or because of the speed of light? Because it is 'round trip' travel? Because there is something about Mars that is special?

You're taking that a bit too far. Aliens who are just like us, would require those things, but life, any kind of life, has some basic universal needs. It would need an energy/food source and to reproduce; that is all. Further, any life that emerged through an evolutionary process, would tend to optimize conditions to satisfy those needs. Their motivations, and decision making, would be based accordingly, and I don't expect that to change, even for a civilization that has been around for billions of years. But you are right. There is a slim possibility it could be ET aliens. Or time travelers, ghosts, fairies and leprechauns. But when that trivial possibility is many orders of magnitude less likely than a 'hubcap thrown in the air', it's probably OK to discount it. As to the technological obstacles to alien visitation, the Fermi Paradox/Drake Equation would have us inundated with alien civilizations, most of which should be much older than our relatively young one. Yet none have made definitive contact. You would think at least one would have, even if others are just playing hide-and-seek with us. Do you think maybe that means technological obstacles to interstellar travel are not easily dismissed ? Or maybe they're too busy with concerns about energy/food sources and reproduction, to send Von Neumann probes to other star systems to gather information which they may never recover.

Again, I do not assert UAP are aliens, they are unidentified, aliens is just one remote possibility, time travelers have been suggested as a possible explanation but I have my doubts about time travel as I am sure most people do. They could be visitors from another plane of existence, or as Jacques Vallée has suggested, quite seriously, that the UFO phenomena is connected with things like fairies, gnomes, and other supposed supernatural creatures from lore. The most obvious thing here is that UAP are just misidentification of known or unknown natural objects but the best data we have doesn't support that premise in many cases... it is these outliers that concern me. And no, "It could have been a picture of a hubcap someone threw", is not a viable explanation. As for alien motivations... you make a good point if you are talking about a civilization that is only a few thousand years since it lived in caves. A civilization that has existed for millions of years might have more long-term goals and data can be transmitted at the speed of light. Trying to guess the motivations of aliens is not a winning gambit.

Thank you! Nobodies making an ass of you and me today. This is why I think Cohen's preface to logic should be required reading. Sick of the magical thinking types of logic and everyone thinking they are Vulcan. I don't even know what is supposed to be meant by "pure logic". To me it's like saying you need a pure hammer or a pure screwdriver. "State of pure logic" is a pet peeve too, sounds like saying you're a complete tool. Well obviously, if you can put a name to it, then it can't be noumena can it? How do you define duration with no objects moving around to measure time with? Why is this an assumption? I thought the beginning was 14-15billion years ago? Lets say I could actually time travel and I start going back, my plan is to travel infinitely back, so I never stop time travelling backwards. It's never time to start travelling infinitely forwards again because from my perspective I've not yet reached infinite.

A list of my fav time travel shows and the premise of the shows time traveling. Outlander - Straight up magic, no technology, and the protagonists alternate between trying to change history and trying to lie low. Timeless- Straight up technology with the intent to change or repair the past time line. Travelers- Technology with the intent of changing the past through major acts of intervention Terra Nova- Technology with the intent of escaping the present by moving to the extreme past. Primeval- Natural occurrences used to time travel and trying to prevent changes to the past and present. Feel free to list your own favs in the poll and I'd like to discuss the differences in the premises of he shows and how well they do in consistency even if the premise is fatally flawed. I'll start out with my fav time travel show which is Travelers, the show is reasonably internally consistent, the main premise is that no material objects can be sent through time only information. Nothing can be sent through time without a T.E.L.L. Time Elevation Longitude and Latitude of the person it is sent to. The main reason I liked the show was... I hate to ruin the show for anyone but while the time travel is portrayed as almost omnipotent technology ultimately they fail to make a difference in the future. The idea they fail is what ultimately makes the show so powerful. Anyone else want to step up and explain their fav time travel show feel free to do so!

Travelers dude! Travelers is the show to watch! Time travel is the bomb!

Time travel is not logically possible if we assume Einstein's theory of relativity is more or less the true explanation of the universe. Einstein's theory of relativity implies a block universe, which is to say that the future already exists, and the past still exists. Ultimately, the universe is a 4d structure that doesn't change. And as far as we know, this entire structure doesn't age in another temporal dimension, and it doesn't exist inside of another spacial dimension either - it simply just exists. Now for an example of the illogical idea of time travel. Imagine that it is the 3rd of January at 11:00pm. You are alone in your house. A week later you have the opportunity to travel back in time (somehow). You decide to visit yourself on the 3rd of January at 11:00pm. Structurally speaking, what happened here, how did this static 4d structure (the universe) change? How can a nonmechanical structure just change itself from being A to being B? Moreover how is it logical that the universe has only you in your house and also has two of you in your house? From what I understand, the universe is made up of events that have their set x,y,z,t locations in spacetime. None of these events move, and none of them appear or disappear. Everything just is the way it is. In general, nothing physical actually changes or moves (I put "physical" because you could argue that a nonphysical consciousness moves through the human parts of this structure, but that's a whole other discussion). How is time travel logically possible?

Mostly I really hate time travel in any show. I generally can excuse one or two bits of magic in something (e.g. faster than light travel is pretty much required to make most Science Fiction work), but the implications of time travel are just too much for me. Having said that, I recently watched Eureka. Pretty much all of the science in that show was just silly. But that then made it easier to accept the time travel episodes. It was all really just fantasy. And the interesting bit of the time travel was that they kept the "timeline changes" in the show. That is, around half way through the run they altered their present by something they changed in the past ... never reverted it. So some characters went on in the show knowing about the "other timeline" and others only knew one. It was like the show was rebooted, with some characters knowing about the reboot.

If there were precambrian rabbits, that would be part of our history and we would not know that time travelers had transported rabbits to the precambrian. My point is that how would we know what is natural and what is the result of intentional time changes? I agree, I am not trying to justify time travel, I am trying to do a thought experiment to see if we could be aware of time changes. Obviously but that doesn't negate the thought experiment. I am not suggesting time travel wars are real I am saying that if they were there would be no way we could know. The idea of a time war taking place in the cambrian ignores the actual idea of war. We would not nuke DC to hurt the Russians, any actions by time warriors would take place in ways that maximized injury to the enemy while limiting any damage to the "home team". An episode of ST Enterprise comes to mind. They were in the middle of a Temporal War, without the help of the actual time warriors I can't see how anyone would be aware of changes in the timeline made in the past since they could not be aware of those changes due to the past changing the present. In the episode Aliens had helped NAZI Germany to win WW2, no one who wasn't outside the timeline had a clue any changes had been made. If someone went back in time to stop Hitler and succeeded how could we know? Our present would not exist and so no one would have any memory of the original timeline... we, as individuals, would probably not exist at all. In all fairness here there does need to be a major assumption here in addition to time travel being possible. The time travelers would have to carry their time machine with them and be immune to the time changes due to this "machine" I just remembered the TV show "Timeless" They had this premise, they could change time and avoid those changes themselves. So my assertion is that we could not detect any changes in the timeline and we would be blissfully unaware of any "time war" no matter how world shattering the time changes were.

SEPERATING SPACE FROM GRAVITY TO TRAVEL FASTER THEN LIGHT AND TRAVEL IN TIME!!! I hypothesize that space is a set size and is not expanding. The notion that it is expanding is a misunderstanding of the effect of gravity on space, time, and light. When we speak about gravity and the bending of light on the plain it is said to curve with the gravitational waves. When we are measuring photons in our calculation of the size of the universe, we leave this part out but it is a fundamental issue in determining distance that is not easily calculated. In the drawing above you can that time, light, and objects or matter move relative to each other along the stretched path of space. If you remove gravity as in the first picture all elements including space is set at 1 light year. In the second and third gravity is introduced and stretches space, which in turn causes time, light, a matter to move along the stretched path. The more gravity the more space is stretched which means the light waves and time is stretched making it seem like the universe has a radius of 15 bil light years across, (according to nasa.gov). What if gravity passed through us or the object that we are flying in, how big would the universe be? With out the affect of gravity on us, we would travel is a straight line allowing us to calculate that actual size of the universe. The illustration below shows what that would look like. Furthermore, by reducing fully reducing the affect of gravity on us it would allow for us to travel faster then the speed of light, travel outside the concept of time which gives us the chance to time travel, and lastly it could explain quantum entanglement. With quantum entanglement we see electrons disappearing and reappearing between atomic layers or moving from the top of the atom to the bottom without evidence of being seen. If the electron is moving free of gravity it can be moving on a linear path but out of our normal view of light and time. So, the electron never leaves the atom or disappear and reappear they just move out of our gravitational affected view of space. The best way to study this is in the ocean with currents. As you scale this up and make it a 3D model it would look like a fish remaining still in the ocean as the current raises, falls and moves left and right. From the fish’s perspective and anything else affected by the current there is no movement. But the ground floor of the ocean or something in the sky above sees the fish as moving. If we swapped the water for space, the fish is moving through time. Also, the amount of energy needed to travel 1000 feet is dramatically greater than in a pool with no current. Imagine riding in a boat on the ocean going over large waves vs a flat calm ocean to travel from New York to England. At the end of the trip the boat that traveled over the high waves and choppy water would have an odometer that reads 4500 miles wile the boat on the calm water would read 3400 miles. From the air and to the boat on the flat water would have the same reading and that would be moving without the effects of gravity and the boat that clocks 4500 miles. In this example we only have tides to go over and small rocking, if we were able to wrap the ocean on all sides of us and still have waves to not just sail over but also around and over/under the distance would not just be significantly greater then the 3400 miles from NY to UK while on a plane or flat body of water, it would be exponentially longer. This means that gravity must be the fourth dimension as it is the only thing that affects height, width, and depth. If we lived in a 3D world traveling a straight path would be easier Conclusion: The Universe is not expanding, the amount of gravity is increasing casing the light waves and matter to move across a stretched plain Gravity is the 4 dimension and things in a 3D world (world without gravity) can move in a straight line in space. If a ship was able to move without the forces of gravity the fabric of space would be flat, smaller, and the ship would be able to travel faster then light and outside of time. All other objects would still be affected by gravity an act accordingly. Reach out if you think you could help with the math. Brandon O. bloldham32@yahoo.com 10/05/2022

When we make a measurement of a physical phenomena, we can only do so by taking advantage of an attribute inherent in the phenomena itself. For instance, we use a rod to measure length. The rod has markings that allow us to measure lengths that are within its boundaries. We use a voltmeter to measure electrical potential differences between two points. The voltmeter uses attributes inherent in electricity and magnetism to make its measurements. This leads us to measurements of time as provided by a clock. All clocks use oscillations of known intervals to measure time. This can be demonstrated in the fact that a sun-dial uses the oscillations as provided by the rotation cycle of the Earth, grandfather clocks use pendulums, and light clocks bounce light between two reflective surfaces. There are many more mechanisms that clocks use to measure time, such as oscillations as provided by crystals, but the point is that they are all based on mechanisms that oscillate. Oscillation in itself is motion and, more specifically, it is motion that repeats with a specified frequency. It is because time can only be measured with motion that motion must be inherent in time. The same statements are true for motion through any other spatial dimension. We can use oscillation to measure our speed along the x axis the same way a speedometer uses the oscillations of the vehicle's wheels to measure the speed of the vehicle. But, if the vehicle always had a constant velocity along the x axis, then we could also measure physical processes in the vehicle in relation to the vehicle's x position. However, we have the freedom to change our speed and direction along the x axis, making this pseudo-temporal dimension unordered. The physical nature of time seems to be one where motion is the only attribute inherent in the phenomena and it is restricted to moving forward along the temporal dimension. If time is motion no different than motion in other spatial dimensions, then how can we expect to time travel to a past that only exists as a memory or to a future that will exist as a memory? We would have moved away from this point in time and would have not made it to a point in the future. If time travel was possible, then I would have to currently exist at all points in time from birth to death. This is because if I could time travel, then it would not be possible for me to take the mass-energy of the entire universe with me and arrange it the way it was back then or will be in the future. Plus, this behaviour is not true for any other spatial dimension. I may have existed at location zero on the x axis, but I am no longer at that position. I have moved on and when I go to visit location zero on the x axis, I find that it is not that same as before. There is always something different such as new cars in the parking lot. Furthermore, If all things exist currently at all points in time, then wouldn't the past and future attract gravitationally? Time may not flow linearly but surely we only exist at a given point in time and not simultaneously at all points. From this view I suggest that time travel to a memory of the past or to a memory that will exist in the future is impossible. However, traveling to a point in time that is parallel to ours may reveal a new view of our universe. These temporally displaced universes would move through time at the same rate as we do, except they are ahead or behind us along the temporal dimension. We could fast forward or rewind time in all instances and show that each universe would have its own unique history, etc... But I have not taken GR into account, so I am looking for people to disprove this view or support it and perhaps we all can learn something to the nature of time.

Time travel is theoretically possible under specific conditions, but the kind of arbitrary time travel you describe is not. Here’s a link from the other time travel thread describing what can and can’t happen with time travel https://www.preposterousuniverse.com/blog/2009/05/14/rules-for-time-travelers/ I don’t see where I ridiculed you or suggested that there was deception. I critiqued your conjecture, and you’ve been here long enough to know to expect that. Getting feedback should allow you to improve your question.

Lots of silly crap is asserted on various platforms online but one of the weirdest is the idea that there is currently a war being fought across time. Of course various bits of "evidence" is asserted but... Let us for a moment participate in a thought experiment. Let's say we want to know if a time war is being fought, how would/could we know? If a time traveler went back in time and changed something, no matter his motivation, could we know? Or, in my estimation most likely, would the time changes be completely undetectable by us, the equivalent of non combatants? If someone went back in time and changed history, imho, we would never know, no matter how violent or destructive the acts of the time traveler were in the past those acts would be part of our history and be seen by us as simply how history unfolded. Even if time was changed a 1000 times in one day we would simply see those changes as our history... completely undetectable as anything but the way things were and are. IMHO. A time war is not just nonsensical from what we know about time travel if it was actually happening it would be something we could never know of... your thoughts?

As I see it, time travel and time inversion are two different things. The former involves "time mixing", i.e., the traveler's body maintains its time while being transferred into a different time of its environment. Of course, the time travel into the future is very much possible - e.g., the SR twins.

I am not proposing that time travel is possible. Interesting concepts but I see them as being in no way any more or less rational that any other time travel concepts and no more or less arbitrary than any others I have read about. Ok then, I still say my thought experiment is valid and that my assertion is valid as well. Boiled down to its most basic. The only person who can know the timeline has changed is the time traveler. Everyone else is carried along in the time stream and the original time stream ceases to exist. Of course this is fictional, the very premise is fictional, but fictional premises can be used to figure out logical outcomes in even fictional scenarios. the idea of course opens up a huge can of worms but they are fictional worms and only have meaning in the context of the fictional thought experiment.

I don’t think this is a true statement. How does it imply a block universe, where “the future” already exists? What future? IIRC the possibility of time travel is limited, it’s not arbitrary. You can only go back to a time after you built a time travel device. edit: #8 https://www.preposterousuniverse.com/blog/2009/05/14/rules-for-time-travelers/

Please bare in mind, whatever follows is not based on facts and it is all just some idea I thought of while reading some experiment. I am no scientist or have any degree in general science. Only computer science. Anyway here goes. So today I was busy reading this article that explained how you could simulate time travel by using a string and 3 people to simulate the pull effect of matter and how it will influence observers attached to that string. (you can google for the article "Step by Step Instructions for How to Build a Time Machine in Your Office in 30 Seconds"). Now, this made me think... If you could create a bubble of entangled particles around yourself. The opposite side of the entangled particles will be bound to some physical object on earth that has been there for however long back you wish to travel (so it must at least exists in the time you wish to travel back to). Once inside of this bubble, you need to be able to freeze the particles you are inside of to negative Kelvin... (yes, I know basically 0 Kelvin is theoretically impossible). But this would cause the particles you are contained inside of to tick negatively compared to their entangled particle and should make you move back in time... This is probably a totaly crazy idea and probably has a pluthora of problems. But I thought putting it in the public space MIGHT help someone out there build on this idea and it might become something (or nothing).

Your scenario “If a time traveler went back in time and changed something, no matter his motivation, could we know?” requires that time travel be possible. They are based on what physics has to say. But there is no scientific basis for this, because it’s not based on science. You can propose whatever you want, but like most fiction, if you delve too deep Into detail you will find problems. How does a memory get erased? How do things broken in one timeline get repaired if they don’t get broken in the new one? But you can propose a different answer and have the same justification that that would be how it goes. An experiment, even a thought experiment, has to have a consistent outcome.

I didn't say it was a complete theory. This thread is about my claim that time travel is not possible with GR. It tells me that you agree with me that time machines are possible, at least theoretically. But I am not only saying that it is unknown whether or not they are possible, I am flat out saying that they are impossible. I gave my reasons in the OP. It makes no sense to even talk about them in GR (except to say that they make no sense). Take a 1 dimensional particle that lasts for 5 seconds for example. Assume there is no force applied to it so that its worldline looks like a long straight 2 dimensional line on a spacetime diagram. In GR, this line doesn't have a past, present or future; it just simply exists. Past, present and future are human constructs. They are concepts in the mind. Since everything is made up of these eternal particles, so is the universe. What if advanced aliens built a time everyday for the past 10,000 years, and they have them, oh I don't know, under some mountains? It allows a lot of opportunity to do illogical things like change the past.

The world is completely connected. Everything fits. The planets cycle the sun the sun revolves around the center of the galaxy, the galaxy spins in relation to the great attractor. Every molecule, every atom has a history and a present state and a likely future condition. No part of the whole can be removed from its current state and inserted in a different time, because the past has already happened in total and the future has not yet happened. The whole universe fits together seamlessly. No way to exist in another time without taking the whole universe with you. If you take the whole universe with you you are effectively where you began. No time travel is possible.

You miss my point entirely, if someone was at war with someone else their goal would be to change time to their benefit not plant rabbits in the Cambrian. While not impossible, planting rabbits in the cambrian might just be the ultimate weapon... but killing a key figure in history would, at first blush at least, seem to be the easiest way to change history. No need to lug around high tech objects with you. Simply knowing the where and when of the target would allow you to pretty much eliminate them at your leisure. Any thought experiment will not be useful if nonsensical parameters are injected into the scenario for no reason other than to disrespect the person trying to honestly understand what we can and cannot know... yes this ties into my famous obsession with certain mysteries. i am trying to understand what can and cannot be known under any or all circumstances. Since time travel is as technically possible as warp drive but also just as surely impossible in reality and this fact has never been used to ridicule anyone who comes up with a thought experiment about what the effects of a real warp drive would be on society. I may not have hit the nail on the head with my thought experiment but my effort was honest and in no way deceptive or meant to ridicule anyone. I would have expected help to make my question better not ridicule to make me look bad.

I watched some of Eureka when it first came out but I lost interest as it progressed. I honestly don't remember a time travel component in the show but I didn't watch very many episodes. I might give it another go!