Travel Definition and 994 Threads

I was thinking about time travel...this is what i came up with ----> lets say person A (age 20,year 2014) travel to the year 2024 and meets himself (A2, age 30).lets say a kills his future A (i.e A2) and travels back in time (which i know is not possible but then). Now A is back in 2014.After 10...

If i have a charge in a vacuum, and I oscillate it at some frequency in x direction, other charges along the x direction will be caused to oscillate in the x direction. So why was I always taught that the direction of oscillation is always perpendicular to the direction of travel for EM waves?

Homework Statement How much time does the object use to travel 12m down a plane. The object has a constant acceleration of 1m/s2 and the starting velocity is 5m/s. Homework Equations S=V(starting velocity)*t+1/2*a*t2 The Attempt at a Solution Here I struggle with changing the formula. I could...

Hi everyone, For one of my project in school, i need to calculate the travel time to the moon. To do that, I thought to use Kepler's third law which is : (2(pi) / P )2 * a3 = GM where : P : period of travel a : major semiaxes (not sure in english, but it is the half the longest radius of the...

Homework Statement You are 20 years old and embark on a mission to a star system that is 200 light-years away. Your ship leaves Earth in 2013 and travels at 0.999c. You do not spend much time at the destination, just head back to Earth. What year is it when you arrive back on Earth? How old...

I'm fresh out of school, and I don't know where to go. All I know is I don't want to stay where I am now (California). I don't know what I'm looking for--maybe I just want to learn more about myself. I've been playing the idea of visiting different cities/countries long enough to get a feel of...

Does light continue to travel through space after its source is removed?

If I travel at the speed of light and have a mirror can i see my reflection? Thanks Any ideas?

Homework Statement The two blocks in the figure are connected by a massless rope that passes over a pulley. The pulley is 16cm in diameter and has a mass of 1.3kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.50 N*m. If the blocks are released from rest, how long...

I'm currently taking a modern physics course, I came across this problem which really threw me off guard: Three spaceships A, B, and C are in motion as shown in the figure. The commander on ship B observes ship C approaching with a relative velocity of 0.83c. The commander also observes ship A...

Of course, I know that time travel is still a science fiction, but I have heard that General Relativity allows this to happen. [reminder of post removed by moderators, as it follows from a false premise]

When deriving different properties from the FRW-metric $$ds^2 = -dt^2 + a^2 (d\chi^2 + S_k^2(\chi) d\Omega^2)$$ -- considering the propagation of light such that ##ds^2 = 0## -- one always assumes ##d\Omega = 0##. But how do we know that ##d\Omega## always vanish for propagating light?

I was wondering what carries the current between two nodes of ranvier (under the myelin sheath) in a neuron. Books and sources say that the impulse jumps between nodes, but I have not found one that tells me how! Is it through the membrane, across microtubules, through the cytoplasm, or...

Consider the following case: First frame S, which is earth. Second frame S', which is rest relative to rocket. Rocket are moving in speed of v relative to earth. Problem: Due to time dilation, from frame of S, the clock in rocket is running slower. Likewise, due to time dilation, from...

Homework Statement We need to create a vehicle that will travel 6 feet, pick up a ballon, bring it back to the start, and then pop the balloon. For power we need to use mousetraps. We cannot modify the balloon, only the car. The Attempt at a Solution We have thought of using a string...

The Multiple universes hypothesis states that there are infinite number of universes, collectively known as the "multiverse". If a person is about to travel back in time, he will create his own parallel universe upon arrival in the past. So if he kills "his" grandfather, a paradox would not...

Can you explain please! thank you.

I am quite uncertain as to why the rear damper is inclined at a angle to the inside of the car. By doing so, does one ensure for rear wheel travel to be along a curved up/down path? i.e I am perplexed as most of the modern rear suspensions are multi-link and have their dampers inclined → This...

I'm going to be at university soon, so I'm not a student quite yet, but I don't think it's ever too early to start thinking about what I will do after university, so; I'm very interested in the way certain geologists work, as they go to strange and quite dangerous places in the world to complete...

Hey i wanted to know if this answer is already present.If yes then what is the shortest amount of distance a beam of light can travel?

Homework Statement Inscribe N chords of equal length within a circle of radius r. A body of mass m travels at constant speed v along the chords and is perfectly reflected in each collision with the circle (there is no momentum change tangent to the circle). Show that the radial momentum change...

Hello I have a question that's been bothering me for a while now and I figured I'd post it here to see if anyone could put my mind at ease. (Sorry if I accidentally posted this in the wrong place) Given that people can only withstand a certain amount of force on their bodies (about 5 Gs)...

After reading about everything I can find on the subject while researching for a story, I've come to the conclusion that wormholes (or "jump" drives or gates) are the only potential "class" of FTL mechanisms which are even remotely (not a problem for fiction) plausible while also not opening the...

An immortal woman who is about to go back in time is mailed a book from an unknown address. Inside the book reveals explicit instructions on how not to die while in the past leading up to the present day. The book is written by her future self and mailed to herself by her future self who is now...

Forgive my ignorance, but If time exists , why is it impossible to travel through it ? From what I know, it is impossible to travel into the past, and also time dilation doesn't really make one travel into the future cause that would mean satellites would've been long gone since things can't...

Homework Statement Over a distance of 3 cm an electron accelerates uniformly from a speed of 9 x 103 m/s to a speed of 6 x 106 m/s. How long does it take the electron to cross this distance? Homework Equations d = 1/2(v0 + v)t The Attempt at a Solution Find t: d = 3 cm /10...

[b]1. the distance between the sun and Saturn is approx. 8.9x10^8 mi. The speed of light is approx. 1.9x10^5 miles per second. How long does it take light to travel from the sun to Saturn? Answer in units of seconds. Homework Equations [b]3. The Attempt at a Solution I have...

I have been doing a lot of regarding about relativistic physics since my earlier posts and I think I now understand the mechanism of the so called cosmic speed limit. This is how I visualize it. I know that the ball on a sheet analogy is not perfect but for this I think it will suffice...

While I enjoy space opera (Star Trek, Star Wars, etc) my favorite fictional genre is the rarer hard science fiction, stories that involve science and engineering which doesn’t yet exist, but, unlike soft SF and fantasy, don’t can be rigorously explained as possible by present-day science, making...

Today I was sitting at my desk where I volunteer and it was kind of slow so I started messing with my desk lamp. I wondered how fast light travels from the bulb to the desk surface, but I didn't know. What I want to know is about how fast does the light travel to hit the desk when the light...

In the context of travel near "c" how is mass defined? Hello all, Brand new member here. I am trying to fully understand the different kinds of masses, i.e. rest mass, relativistic mass and inertial mass as well as any other kinds of relevant kinds of masses I am forgetting about, in the...

There is no edge of the Universe. Alright, I kinda realize this, I'm not a layman. However, nobody addresses what would happen if you traveled far enough. There's only a limited amount of matter out there and going off the theory that the volume of our Universe is finite, there's 'an edge'...

Suppose you were to board a ship on Earth departing for a star system 1,000 light years away. You accelerate at 1g for the first 500ly, then decelerate at 1g for the second 500ly. Observer on Earth will claim 1,001.936 have passed during your voyage, whereas you will have experienced 13.452...

This has been bugging me. Several respected propulsion scientists at the 2008 Joint Propulsion Conference claimed that interstellar travel within a human lifetime was impossible. The KE of a rocket traveling at a significant fraction of c would be enormous via KE=0.5 * m * v^2 and that...

So, I've been learning about quantum mechanics as of late. If I understand correctly, there would be a large amount of energy required to "turn back the clock" on all particles throughout Earth (assume that I don't change the position of satellites or the stars) in order to go back in time...

How long would it take for an asteroid to travel to our "sun-system"? I have been informed about the rules of the forum, that the administrators strongly encourage members to make an effort on their own first to sought out answers, but that one mustn't do that. I'm very tired of Wikipedia, and...

Hi, I don't know if I am in the right sub forum or if this topic has been discussed but I'll ask anyway. so I don't think travel into the future beyond what hasn't happened yet is possible and believe it or not, it sounds more possible to me to travel into the past since the past already...

I was just thinking about how cool it could be to time travel, but I don't know if it's technically possible. The only Physics class I took was a first semester calculus based physics class so I don't know if they ever talk about time travel in other physics classes. I don't know if this is a...

People seem to be getting confused with the concepts involved in some of the faster than light travel methods that have been theoretically proposed. No, it is not possible to travel faster than the speed of light through the normal, physical universe in our current understanding of physics...

The proper mean lifetime of ##\pi## mesons(pion) is ##2.6x10^{-8}s##. Suppose a beam of such particles has a speed of .9c. a) What would their mean life be as measured in the lab? b) How far would they travel(on average)before they decay? c)What would your answer be to part (b) if you...

Your choice of least "facepalm-able" space travel mechanism If I may use the "facepalm" meter of Sci-Fi hardness. Examples The film Gravity, in which only the astronauts in your audience would complain loudly about technical details such as how quickly Sandra took off her space suit, has an...

Homework Statement If you can hit a golf ball 180m on Earth, how far can you hit it on the Moon?The Attempt at a Solution Since this question deals with range; sx = [vxi^2 sinΘ]/g My problem is that I do not have the velocity at which the golf ball is being hit. As for the launch angle, I...

http://arxiv.org/pdf/1312.7128v1.pdf

Hi, Can someone please help me understand these two situations? 1. When an airplane is flying from point A to point B, is Earth stationary from the point of view of the plane? While I am not sure, I think the answer to this question is yes, because a plane flies within the atmosphere of...

Refractive index----- will it travel back along the same way? From the picture http://en.wikipedia.org/wiki/File:RefractionReflextion.svg If I travel a light ray from n2 to n1 , I think the light ray will travel in the opposite direction shown in the first picture. But what about the...

Length Contraction:Does the object or travel distance shrink? I had always thought that length contraction meant that the object itself shrunk but I stumbled across an article where they said "Because of length contraction the photon doesn't travel any distance at all. Which is it? Any help...

Hi Suppose an astronaut is accelerated to the speed of light (OK to one part in a million less than the actual speed of light ) and makes a journey to the event horizon of a black hole that is ,at the outset of the journey and hopefully also when he reaches it) 100 light year distant...

Very interesting bunch of guys trying to get a man into suborbit as cheap as possible. Found their website and youtube videos links at the bottom. Thought I would share. They have interesting video's of engine tests as they try to design the first rocket to send a man into space...

Homework Statement A block starts from rest at the top of a 31.0 degree inclined plane and encounters a spring, of constant 3.4 kN/m, rigidly attached to the plane. If the block's mass is 33.0 kg and it compresses the spring by 37.0 cm, find the distance the block traveled before it...

Hi, I'm looking for time travel stories (preferably movies) without paradoxes (grandfather paradox and similar). Also, I'm not looking for stories that try to explain changes in the past with the creation of alternate timelines. I'm talking about stories where people travel into the past and...