wazzuuup

If travel to the past were possible, any person could become a millionaire. Pretend you had one dollar in your pocket. Then if you went back one second, you could take that same dollar and you'd have two. Then you go back another second in time and again you take that dollar. This is a never ending story.

Tachyons are hypothetical particles that are said to go faster than light. As in, they really travel the same distance as light and go faster. They could never go slower than the speed of light and if one were to appraoch you from a distant star, it would look like it is actually traveling away from you since the light that reaches you first is that showing it hit Earth.

In fact, the value for c has already been applied to many useful relationships. For instance, before Einstein, physicists always measured time in a sacred unit, called the second, different from the unit to measure space. No one suspected the powerful results of using the same unit for both, or of squaring or combining space and time separations when both were measured in meters. Time in meters is just the time it takes a light flash to go that number of meters. And thus the conversion factor between seconds and meters is the speed of light! Such has lead to the Einstein-Poincare discovery in 1905; showing that now two individuals can disagree on separations in space and time; but agree on thet spacetime interval. Furthermore, there is no law of physics (so far I know) that forbids superluminal travel, so the speed of light is perhaps not the limiting speed.The only complication is that nothing can cross the light barrier; thus classifying all objects into three main groups according to their speed limits. The first class is slow moving things of the everyday world around us (you, me, stars, etc). All scientists agree that this class exists. The second class is one where subatomic particles move only at the speed of light. These particles, like photons or neutrinos, have never been detected to have slowed down or speeded up. The speed of light is a constant due to the fact that time, distance, and mass are not the same for all observers. The third class is tha tof superluminal objects. called tachyons, that move faster than light. They are accomodated by RT and would never be able to travel slower than the speed of light. Currently, there is no evidence for their existence. But think about it. If a tachyon were appraoching you from a distance galaxy, it would actually look to you like it was with you and then moving away from you. This is because the light, which allows you to see the object, can only move at one speed. Thus the photons showing the object closest to you would have arrived at your eyes first, showing the gradual journey of the tachyon moving away from you. Thus it would, according to the observer, travel backwards in time. My point is that because of the universal property of light to always travel at a constant speed, and all our 'human and invented' notions such as time, distance and mass are directly affected, it is only natural to want to know why the lightspeed has such a massive impact. But if everything could just go faster or slower than the speed of light, our universe probably wouldn't be able to operate. If one object could first travel forwards in time, and then backwards, there would be no arrow of time anymore.

This is just a thought. Light is the fastest speed we know of, traveling at roughly 300,000 km/s. According to SR, anything that travels faster would in fact be traveling backwards in time. So if there would indeed be jinn particles (faster-than-light particles), we wouldn't be able to see them since we are traveling forwards in time, and not backwards, with them.

What's interesting about time dilation is that if you were traveling in a spaceship at say 90% the speed of light, not only would the people on Earth see your time to go slower than theirs, you would actually see their time to go slower than yours if you peered out of your window. It would seem like hours to your for someone on Earth to tie their laces. So it works both ways. This has nothing to do with any mechanical oddities; in fact both you and the Earthling is correct in the observations. HOwever, only if you land on Earth, would you, the traveler, be younger than the Earthlings since less time passed by for your relative to Earth. Time dilation goes combined with width contraction and mass increase as well. This means that Earthlings would not only measure your time to tick slower, they would think your spaceship got narrower, and increased in mass. Again, this works both ways.

I just turned 15

It reminds me of blowing up a balloon. If you mark two points on the intial balloon and then blow it up, these points will still be on the same spot, but spread out more. Yet the spots would have enlarged as well, wouldn't they? I'm not sure if that's a valid analogy to compare coordinates with, but here again you come across the dilemma on how to coordinate the two marks on the blown up balloon. I also wanted to share my idas on my response to the question "what is time?". 1). It is the duration (of the notion) of any changes in space. 2). It is not universal, but relative to its measurement of the change in space. 3). The only universal time is relative to the rate of expansion of the universe. 4). It is different than the one Einstein derived in the sense that : dt=dx+dy+dz, whereby x,y,z are 'local' variables, whereas Einstein's formula is whereby x,y,z are the three spatial dimensions 5). time is always positive 6). Travelling at the speed of light implies there is no light in front of you, so one can't experience anything and therefore have no notion of the change in space, which implies dt=0. Just to put this in context, if someone states his age is 21, it means she or he has changed in space for 21 years. The change in space is also for a large part influenced by matter, which therefore changes space and time in acordance with Einstein's curvature of spacetime. If there's space, there can be time if a change occurs. If there's space, it can be without time if no change occurs. If there's no space, there can't be any time for no change occurs.

I seriously doubt backwards time travel. Special relativity emphasizes on the 'space time'. So if time is discontinuous stated by quantum mechanics, we will never be able to get back to the same time and location of yesterday. Why not location? We rotate on Earth, while rotating around the Sun, moving around in our galaxy, in our expanding universe. So the place in which we went to the store yesterday, is thousands of kilomters away now and untracable since all the reference frames are moving at their own space time rate. I'm not saying that the space time in which we went to the store yesterday just disapeared, but has a different coordinate now. With location gone, and time being discontinuous, you can't just 'pull' the time back to go backwards. And since faster than speed of light travel is forbidden by e=mc^2, I guess nobody will ever be able to go backwards in their own proper time (or forwards in your own proper time and backwards in coordinate time).

How can photons be massless when at rest, since intuitively it seems like nothing can be massless if it is made up of something. How could gravity act upon massless things, I always thought that masses attract each other, so how can massless photons be attracted? Is it correct that when photons move at high speeds, the energy is the mass, so when they are at rest, there is no mass? I am so confused…

In this forum, we've been discussing mostly time. I think time couldn't exist without energy (negative energy, positive energy). This would mean that once there are any quantum fluctuations, sounds, or perhaps humans walking down a street, time would gain a function. This is probably the same as saying that time passes with movement, but movement gains energy when accelerated so it seems better to just directly relate it to energy. My main question is whether there could be any way to calculate the 'speed of the proper time' relative to (... nothing........)? (Could it be related to the energy, the speed of light or anything else?) I just don't find it 'correct' to actually compare it to a coordinate time, finding a relative speed. I am not trying to say that there is a universal time, only that there should be a universal method to calculate the speed of time (assuming such a concept of 'speed of time' has a truth in it). But I think I learnt at school that energy can never be lost, since it is just converted into a different type of energy (so time can never stop?). If temperatures however dropped to -273 degrees Celcius, I think I read there would be no energy, entropy, etc. Are both claims correct? But I don't understand whether the continually falling entropy from the second law of thermodynamics allows the total energy to stay the same, and whether gravity is a type of energy (if it is, this could fit in where the energy of the gravitational pull makes time time run slower according to GR). However, last year I got into ninth grade and my teacher mentioned 'gravitational energy', but then in books Einstein refers to it as a 'field', while Newton said it was a 'force'. So is it or is it not a type of energy?

Thanks Tormod (and Uncle Martin and FT!) for having helped me clear up my thoughts, especially the difference between time dilation and time travel had been troubling me.

I hope you guys understand what I was trying to put foward (I'm not that strong in communication).

I once read that time 'jumps', meaning it's discontinuous. It's difficult to imagine this, but it's just like a movie; when there are 24 or more images per second passing, we can't see these seperate pictures, so we get the impression that it flows. These seperate time units, time quanta, would be 0.5391 * 10^-43 seconds. The formula of the Planck time is: T = (GH / c^5)1/2 (H=h/2pi) I must admit I haven't particularly examined the wormhole or superstring theories for backwards time travel, but it seems illogical to me that you can reverse time which is made up of tiny units just following each other up. You can throw a rope, and pull it back because all the particles that make up the rope are connected. But time quanta isn't made up of anything, so the unit just ends after each Planck time. Pretend you go back 30 years in time using any backward time travel theory, it would have taken time for you to do this (because you can't time travel without travelling in space, and thus travelling in space takes time). Thus I would like to hypothesize (without much support I admit) that you would still be older than when you decided to go back in time. If you reverse your movements, your time still ticks forwards. Pretend I am wrong that reverse in time is impossible(which is very likely. I have never seen any proof that backwards time travel is impossible). If you really reversed the time, you would have to reverse your actions as well because the time quanta is stuck to the changes in space of that time interval. We ignore my thought that the time quanta from thirty years ago already 'stopped'. In this case, you would actually become younger, until you didn't exist anymore because you weren't born yet. This doesn't seem to make sense because your memory would have to shrink, etc. If you actually 'saw' the original copy of yourself, this would again bring up the well known paradoxes people have mentioned. But because the 'future you' wasn't there in the original version of the past, some people came up with the idea that there exists parellel universe. To me, this seems very far fetched. How would you happen to land in this parellel universe? While writing these paragraphs, I thought of something else. If we again assume it's true that time is discontinuous, this would mean that in the interval between two units of Planck times, there would be no time. Only in this case of 'no time', would you be able to travel forwards or backwards. It would take 'no time' to travel from a 'no time interval' somewhere in the year 2004 to a 'no time interval' somewhere in 1500, or somewhere 400 years after the big bang (if there was a big bang). 'No time intervals' can't stop existing because they never existed. But such an idea for travelling back in time has the problem that this would contradict my idea that you can't travel in time without travelling in space, because the 'no time intervals' can't allow any space travel (or any other change), or else you will land in the consecutive time unit again which is the time we only perceive. Thus again, it seems impossible to travel back in time.

To Freethinker, thank you for all your replies, you've helped me improve my communication and thoughts. But the more I read on these forums, the more confuzed I get. For example: on 07-08-2004, in the forum 'What will be the changes if we move from 3D to 4D', GAHD said, "Every experiment that has shown any dissonance in clock 'tics' can be disproven, or has had massive amounts of data doctored or just plain ignored (like the Hafele-Keating Experiment). NO ONE has been able to show time dilation occurs except with math (which then breaks down in real-world applications)." This seems to contradict everything. I do believe that time dilation has been applied to application. Muons are particles that are produced when cosmic-ray protons strike air molecules in the upper atmosphere of our planet. Normally (at rest), they persist for about two millionths of a second before decaying into energy and other, less massive plarticles; hence none of the muons should reach the ground. However, apparatus places at sea level and atop Mount Washington, New Hampshire, was ale to detect the fast-moving muons and to measure a significantly longer tifetime for them; relative to our fixed (Earth based) reference frame, their 'natural clocks' had apparently slowed down. In fact, while traveling at 99.4 percent of the velocity of light, muons endure for about sixteen microseconds, an eightfold increase in their usual lifetime. This time extension matches to within 1 percent that predicted by Einstein's theory of special relativity. (I got his information from a book "Relatively Speaking" by Eric Chaisson).

Do you IRC? What would IRC mean? I'm sorry, but not everyone's first language is English. When I copied and pasted that equation, it was a square root, but when I pasted it in the forum, it suddenly turned into a question mark.. the rest is self-explanatory. But anyways, back to the topic. I didn't want to go into any etymology or termonology of the word 'time travel'. My apologies. I was just wondering if you could reverse or accelerate in time without moving. Theories about wormholes, superstrings, time warps, Godel's Universe etc. all include space.This is why I thought of naming it 'space-time travel'. I agree that when one person/ object is in motion compared to another, they will have different "time dilation" components. But would this imply that every single moving object would time travel, despite the miniscule slow-down factor? And isn't everything moving?

* the ? stands for a square root in the above equation

But, if you were to move at 99.9 % the speed of light for five years towarsd Alpha Centauri, and then come back again (taking another five years), 70 years would have elapsed on Earth. This would be calculated suing the equation dt= 1 / ?(1-(v^2/c^2)) * dT dt would be the coordinate time (earth time) and the dT would be proper time (travelling 10 years) However, my argument is that you can't achieve any time dilation or other form of travelling in time where your time is different to the surrounding world's without travelling in space. THus, we should call time travel space-time travel.

If one were travelling with one 'Earth second' per 'Earth second' in time on the planet Earth while going from point A to B, it is not 'time travel', because the difference between your time of departure and arrival times in the surrounding world equals the duration of the journey ondergone by the object.

Hey everyone, One standard definition of time travel is that of David Lewis's: an object time travels if the difference between its departure and arrival times in the surrounding world does not equal the duration of the journey undergone by the object. I therefore believe that you can't travel in time without travelling in space. Wouldn't we therefore have to call it spacetime travel? Please argue anything, I'm a fourteen year old girl working on a project. If I am wrong, I would please like to know!

hehe thanks

I'm fourteen and I think I want to become an astronomer later. Astronaut was my first choice, but I'm short sighted.

Stephen Hawking explains it in his book The Universe in a Nutshell

I was wondering where I could find this time travel quiz? It seems really interesting!

Heya! For school, we're doing a personal project and I wanted to focuss on time travel. Would you have any (not too complicated) information? Do you think it's possible to come up with my an own impression for time travel? I was wondering which theory would be the most realistic. THANKS so much for your time!