Travel Definition and 995 Threads

so they say we can't travel back n time because it would create a paradox. Theres a line of thought that's says it may be possible i we select the history that does not cause a paradox. However it seems to me that quantum physcics also says that all historys exsist until we collapse the wave...

In trying to understand electricity I thought of the following: If I set up a wire one light year long, stretching out into space ½ a light year out and ½ a light year back, and connected a series of light bulbs all the way around the wire, and then connected a battery (large enough to handle...

Does quantum entanglement allow information to travel faster than light? http://en.wikipedia.org/wiki/Faster-than-light if you scroll down to quantum mechanics.

As I have read, a clock in a spaceship approaching the speed of light will appear to slow down in time from the point of view of an outside stationary observer. Does the direction of travel of the spaceship relative to the observer have an effect? If it is traveling towards the observer it seems...

Are there any other particles besides tachyons that time travel backwards?

Hello, I'm a high school senior interested in studying physics in college. I was listening to a podcast by Neil deGrasse Tyson in which he stated that if one could travel faster than the speed of light, it might be possible to travel back in time. He didn't really expand on that so I was...

Hello! I'm redesigning my never-to-be-finish sci-fi novel, yet another futile to come up with scientifically based interstellar travel propulsion. My latest consideration is based on article[1] and possible extensions of those ideas. Anyway, I'm looking for an independent opinions on the...

Does no-cloning theorem contradict with the possibility of time travelling? If i send a photon back in time from t1 to t0, then between t0 an t1, I could have two identical photons, in other words, i can use the time machine to clone my photons. Have I missed out something?

If one of the problems with time travel is the paradox's it creates, if we take the multi-worlds theory into account where there are an infinite amount of universes and hence a infinite amount of possibilities why in one universe could there not be entropy be decreasing instead of increasing and...

I might get a bit of a reputation for space talk, here :P So, I'm familiar with the concept of Photon Sails, but I was wondering how effective these would be? To make sure we're on the same page, I'm talking about using a highly reflective surface to propel a spacecraft by hitting it with a...

Problem statement How fast must a neutron be traveling relative to a detector in order to have a measured kinetic energy that is equal to its rest energy? An "attempt" I know Ek = mc^2 - m0c^2 But if Ek = m0c^2, wouldn't the two terms cancel out from this equation? I am having trouble...

1. Homework Statement Find the time taken to reach half the maximum angular displacement in a PENDULUM. Given that the bob hanging at rest was given an initial velocity of 2ms, and the length of the string is 6m. 2. Homework Equations finding the angular velocity using sqrt.(g/l)...

Suppose a civilization had the technology to make wormholes. It would likely place them in orbit over its planets. Say one end orbiting Earth and the other end orbiting Mars. Now, it makes sense that gravity would travel through the wormhole, and the planets would alter each others' orbit. To...

Which types of engineers usually travel the most? Which types of engineers usually travel the least? I think I traveling over to a certain country for say 4-5 days and then go to a next assignment would suit me well.

for quite some time, there has been the thought that once a species has evolved far enough to really travel in space, they have lost their greed, etc., such that they are not dangerous. i am not sure that i buy this. i realize that i have only the observations of one species with which to...

it is often stated that time travel is not forbidden by any law of physics. but doesn’t the second law of thermodynamics forbid it because going back in time would involve a decrease in entropy?

Hi, Today I was sitting in the train and I wondered what the motivation for a time traveler would be if he wanted to go in the past. Say that I live in 2011 and I went back 210 million years ago to see the dinosaurs, that would be my motivation. But when I would travel back to there and...

Hello Friends, I need to find out who is currently THE TOP expert in the US in black hole, worm hole and time travel theories. When I last checked, it might have been Kip Thorne or Stephen Hawking, but perhaps there are others who are also prominent. I would love to hear your opinions...

Let's say we track a photon... starting from sun and reaching earth. When the photon moves through space (maybe because there is vacuum) it looses no/little energy. Now... when it enters atmosphere? When it goes through glass plate? or through ocean or through water vapour? Does it slow...

From my intuitive perspective on time dilation. The faster an observer is going relative to another, the slower in time the observer moves with respect to the to the other. However, I always pictured that this only works if the observer is moving away with respect to an observer at rest. Since...

This may be a bizarre idea, even idiotic idea but could you move sideways through time? I have heard that time may flow differently in various places. We experience a forward flow of time whereas some other planet in our universe could experience a reversed flow of time. However, if time is like...

Q: if you travel closer to c, will you see length(distance) contraction between andromeda and earth?

What is the shortest distance you (or anything) and travel? Is there a limit? And if so why?

Let’s say someone travels one year in the past to change their own lives coarse, maybe lotto numbers or something else. Doesn’t matter if time travel is possible or not, this is just a thought experiment.? The problem I see is that somehow you’ll have to duplicate the nuclei that make up your...

I'm hoping someone can clear something up for me. I was recently asked if someone traveling close to the speed of light toward a star would see that star's light as gamma rays. I argued that they would not due to their perception of time slowing down, whereas someone else argued that...

Please can somebody explain to me how and why light travels through glass into our eyes, as it doesn't in opaque objects?

Hi everyone! I'm a pilot on a private jet, in conversation one of the crew mentioned that "You get younger when flying." Now I had to correct him saying that actually it's just that time slows down as you go faster. Unfortunately for the flight attendant, going faster also means that she puts...

Homework Statement A beam of red light entering a block of glass (n = 1.52) 10.00 miles thick will emerge 1.75 miles ahead of a blue pulse that entered at the same moment. (a) How long will it take the red light to traverse the glass? µs (b) How fast does the blue pulse travel? m/s...

I can't figure out why it should. Here's what I'm thinking: - Light is affected by the gravity, and gravity is the interaction between masses, so surely light must have mass in some form. - Light has no mass, but has energy depending on the frequency of the photon. By E = mc^2, photons...

I'd like to share some thoughts I have had on faster than light travel, and hear from you if it really can be that simple. In short, it can be said that if we believe to have proven the relativity of the speed of light, faster than light travel is, by definition, impossible. No formulas, no big...

I was wondering if such could be possible in the future, to travel from one spacetime to another (if other spacetimes exist)?

Hey y'all, I've been lurking for a little bit and just reading since I'm not as knowledgeable as many of y'all. I'm a university student preparing for web design/database administration but consider studying physics/cosmology my (only) hobby. My question is about the requirements for light...

greetings, why does the low frequency radiation or wave can not travel for longer distance? advanced thanks.

OK I'm still new to cosmology and this question is bugging me: if a photon is emitted toward me from a distant galaxy at a distance D, how do I calculate the time it takes to reach me? I assume the universe is expanding exponentially with a DeSitter scale factor a = exp(Ht), (H = Hubble...

greetings, how does light travel through the glass? advanced thanks

This is a conversational post, I am looking for others opinions on the diagram below related to time travel. If it is in the wrong room, please move it to the appropriate location. Thank you. I look forward to hearing your opinions...

I'm not a physics student but have always been interested. That said my knowledge is very slim. I've always wondered why traveling faster than light would lead to time travel, I've poured over websites and other forums but they tend to descend into physics that is beyond me. Here is an outline...

Ronald Mallett, PhD is a renowned physicists known for his proponents on the idea of time travel. Mallett uses his background in physics and mathematics to support his idea to build a time machine, using Einstein's Theory of Relativity as a basis. Do you think this is even possible? Right...

hi All, why is this? some matter has a refractive index of slightly less than one for light in the x ray region. This implies a phase velocity faster than c, right? could someone explain what is actually happening here? THANKS!

I was discussing with my E&M professor the idea of faster than light information exchange, which of course we found to be impossible, it didn't take much analysis of the simultaneity of events as seen by Einstein to realize that faster information travel than light would completely change the...

or the same speed than if it had a counter-clockwise spin?

Homework Statement Jack and Tim were standing in the main street. The distance between the boys was x metres. At the same moment the boys started to move. Jack was running at a m/s and Tim walked at b m/s. Homework Equations Find the time when the boys met if a) they moved towards each...

The paradox, is basically a theory about time travel. This thread requires the assumption of making time travel possible. Supposedly, you go back in time and kill your grandfather before he gets married. How did you end up there in the first place?

I want to confirm that the TEM wave is actually travel inside the dielectric between the two plates of the parallel plate transmission line. So even though surface current and surface charge appeared on the surface of the conductor plates as the consequence of the boundary conditions between the...

Good Afternoon, After watching a TV program "Into the Universe" "Time Travel " I have some doubts left. I know Time Dilation has been proven by experiments (Atomic clocks on jet plains) and we see it every day that GPS system needs time correction (Due to Time Dilation perdicted in SR)...

I've been doing a problem that requires me to find the time taken to travel a certain distance if I know the initial acceleration of a body at the starting position and its initial velocity (starts from rest). The acceleration is a function of position a=-GM/(Ro^2). So say a body is released...

Let's say you have a DC circuit with a capacitor and a resistor. How does electromagnetic energy flow within the system? Through the wires? In space between and around wires? N.B. Why/how would EM energy flow in the first place?

I'm pretty much a newbie to this quantum physics stuff, but the one thing that really blows my mind is the double slit experiment. I just don't make much sense. Anyways, I was wondering, could the interference pattern caused by firing a single particle through the double slits be the case of...

Hi every one. Im new on this forum,and my question is my reason for joining. iv seeked this question for a long time now,and it confuses me.The answer may be very simple to a peron that already knows the answer,me on the other hand... ! hasnt got a clue...

Do photons actually "travel"? since, at the speed of light, time does not exist and there is effectively no distance between any 2 objects in the universe, and since QM demonstrates that photons "take all possible paths" (ie, they are essentially everywhere between the time they are emitted and...