What is Travel: Definition and 998 Discussions

Travel is the movement of people between distant geographical locations. Travel can be done by foot, bicycle, automobile, train, boat, bus, airplane, ship or other means, with or without luggage, and can be one way or round trip. Travel can also include relatively short stays between successive movements, as in the case of tourism.

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  1. rekha1804

    B Medium of light travel in space

    What is the difference between space and vacuum? Since light waves require a medium to travel, then what is the medium in space?
  2. S

    B How did expansion take 380,000 years to let light travel freely?

    Here's as far as I've gotten in the research (please correct any errors I'm making). The stages of high density had included these periods: • light at high energy was in a cycle of forming into matter, forming back into light, and so on • until things cooled enough for nucleons to form •...
  3. jedishrfu

    B Time Travel: Is it Physicsly Possible? | Scientific American

    https://www.scientificamerican.com/article/is-time-travel-possible/
  4. Marcarious Thomas

    B Faster Than Light Travel: Exploring the Possibilities of Spacetime Curvature

    Based on the current understanding of general relativity, it is possible that curving spacetime in the back of a spacecraft would allow for faster-than-light travel. In general relativity, the curvature of spacetime is determined by the universe's distribution of matter and energy. If a...
  5. J

    Is the Speed of Electricity Affected by the Length of the Wire?

    300 000km connect light bulb and battery. I would say 1sec is need from I turn on switch to light start lighting. This video say it is 1m/c...Is this video wrong? Do electron travels thorugh wire, if 300 000km wire is connected to bulb ,why electricitly travel through space only 1m??
  6. jselms99

    Time Travel: Calculating Velocity for 10 Year Trip

    So at first I thought that the time would be 10 years, and that I’d have to consider the outbound motion as v = .87c and inbound motion as v = -.87c but I’m struggling with addition of the velocities and whether or not this is even the right approach?
  7. haziq

    Problem 2 in "Quantum Theory for Mathematicians", Solving for the travel time of a particle in a potential

    I’ve been trying to solve this for ages. Would really appreciate some hints. Thanks
  8. paulimerci

    At what angle must the boat travel so that it moves in a straight line

    I'm assuming the boat is traveling north at an 8 m/s and the river is flowing east at a 2 m/s. For the boat to move in a straight line, it has to aim at an upstream angle given by #theta#. Using SOH CAH TOA, ##v_r = 2m/s##, ##v_b = 8m/s## $$\theta =\sin^{-1} \frac{v_r}{v_b}$$ $$\theta = 14...
  9. C

    I Effects of time dilation for near-speed-of-light travel

    Hello everyone, I've been learning about special relativity, and so far I believe based on what I read that if you are traveling at a velocity of .6c, you will experience time 20 percent slower than people on earth. Each second in the spaceship will be 1.25 earth seconds. Each second on earth...
  10. ForTheLoveOfPhysics

    Time Travel: Setup & Challenges for Safe & Accurate Travel

    I like time travel for entertainment purposes in books/movies but there’s one fundamental flaw I haven’t seen discussed. Any time travel example without the use of a ‘gate’ or wormhole (Star Gate SG1 for example) focuses on time only. The problem with these is you need to firstly travel in time...
  11. P

    A Time Travel, General Relativity & Information Paradoxes

    General relativity permits some exact solutions that allow for time travel. Some of these exact solutions describe universes that contain closed timlike curves, or world lines that lead back to the same point in spacetime. I wondered if these solutions also permits Causal loops? Such as the one...
  12. D

    B Would light travel in a circle at the edge of the observable Universe?

    Is there sufficient mass within the observable universe’s volume to form a black hole event horizon around the observable universe and, if yes would light fired tangentially at the edge of our observable universe ever loop back around in a circle or spiral inwards?
  13. N

    Can a belly button ring travel through a person like a bullet?

    My 15 y/o daughter is in driver's ed. Her teacher passed on some information as fact that seems more like an urban legend. He told the class that an inexperienced driver got into a bad car wreck, and the sudden loss of speed caused her belly button ring to penetrate her entire midsection like...
  14. MrSimp

    B Does Force Travel Faster Than Light?

    Imagine a plane 1 light minute across. Now imagine 1 person on either and of that plane. Between them, is a thin indestructible bar that is 1 light minute in length. In the center of this plane, a simple device has a wire that leads to a motion sensor on the left side of the bar. If the left...
  15. B

    B (ELI5) why can’t massless particles travel infinitely fast?

    I feel like if something is massless it should be able to travel infinitely fast with any amount of energy. When you have something with mass, you would need an infinite amount of energy to push it infinitely fast, but if the thing you’re pushing is massless, you should be able to push it with a...
  16. C

    I Calculating Relative Change in Travel Time Due to Spacetime Perturbation

    Suppose you have the following situation: We have a spacetime that is asymptotically flat. At some position A which is in the region that is approximately flat, an observer sends out a photon (for simplicity, as I presume that any calculations involved here become easier if we consider a...
  17. O

    I Does gravitational energy travel like electrical energy?

    Electrons flowing through a resistor are dissipating electrical energy. The electrical energy is transported from the battery to the electrons along the curved field lines of the Poynting vector. It seems like a meaningful idea that electrical energy necessarily travels from the source to the...
  18. Spockishere

    B Travel 7 Light Years at 50000km/s - How Long?

    let's say i would like to drop by one of my pals on a certain planet, 7ly away. I got to 42 years but it doesn't really sound correct.
  19. A

    I Time Travel in Newtonian Spacetime: Is it Possible?

    Is time travel possible in Newtonian curved spacetime?
  20. K

    A A Question about time travel.

    If time travel were possible, could someone alter or set up the way they want things to happen before they went back to their desired destination?
  21. karush

    MHB 51 How far will the car travel in 10 sec

    How far will the car travel in $10$ seconds" \begin{align*}\displaystyle \Delta t&=10,\quad a=2,\quad d_i=0,,\quad v_i=0\\ d_f&=d_i+v_i\Delta t+\frac{1}{2} a \Delta t^2=0+0\cdot 10+\frac{1}{2} \cdot 2\cdot 10^2=100 \, m \end{align*} or $\displaystyle v=\int{...
  22. V

    CDC Level 4 Travel Alert -- Doing the Math

    The 4 level system categorizes international destinations at a level four the 28 day infection rate per 100,000 > 500. The population of Costa Rica is 5,094,000. The WHO had 5,488 infections for 2/11/2022. How would you calculate the infection rate per 100,000? 5,094,000 ÷ 100,000 = 51 5,488 ÷...
  23. K

    B Experience Travel on a Photon: Hitch-Hiker's Guide to the Universe

    We know that as speed increases, time slows, and at the speed of light time apparently ceases. Imagine a hypothetical hitch-hiker sitting on a photon and speeding through the universe at -- well, the speed of light. If time has stopped for him (her?), what is his experience of his journey? Are...
  24. V

    B CDC International 4 Level Travel Notice System Math Calculations

    The 4 level system categorizes international destinations at a level four if the 28 day infection rate per 100,000 > 500. The population of Costa Rica is 5,094,000. The WHO had 5,488 infections for 2/11/2022. How would you calculate the infection rate per 100,000? 5,094,000 ÷ 100,000 = 51...
  25. Borek

    Power surge video - why does the spark travel?

    Any idea what is the physics behind? Why does the spark travel down the line?
  26. S

    I Why does light travel slower in water?

    I always thought it was from individual water molecules absorbing and reabsorbing light, but this explanation in a video from Fermilab is very strange to me . What is this "new wave" he speaks of; wouldn't it be light too? If so, then this light is now slower than the speed of light, which...
  27. chwala

    Find the time taken to travel from top of slope to base - Mechanics

    Now this is a textbook example with solution. I understand working to solution...my only reservation is on how they used acceleration. The cyclist, i understand was traveling at a constant acceleration of ##2## ##m/s^2## before reaching the top part of the slope. Now, if he is descending...
  28. M

    B Time Travel: Is It a Meaningless Concept?

    Assumptions: There is no "absolute" time, time is all relative. Taking the twins paradox as an example, both twins measure a different proper time when they re-unite due to each twin taking paths of differing lengths through spacetime. Conclusion: Time Travel itself is a completely...
  29. J

    B How far do photons travel inside common lasers?

    So (wildly simplistically) lasers work by photons being reflected between mirrors gaining energy on each trip through the medium until they break through the mirror on the output end. How many trips does that typically result in? 10s, millions? And thus the total distance is that count * the...
  30. P

    Using Monopods for city travel utilizing linear induction motors

    This is another open ended question, exploring a space of design concepts, in similar spirit to this. I want to explore monopods with regard to travel in densely populated cities(even possibly intercity travel). The main idea is to use small personalized pods to travel in tubes(or tracks). The...
  31. D

    Exploring Electron Rockets for Interstellar Travel

    Hi all, Why not build an electron rocket? Why won't this idea work? Seems like someone could just hitch an electron gun onto a spaceship. Boom! Electron Rocket. I was thinking about ion thrusters. These use ions to achieve thrust. They are problematic for achieving a high delta V because...
  32. Zeeshan Ahmad

    I Time travel is a fact or fiction.?

    In my search about time travel for Is it possible or just a fictional thing as many of our estimed scientists and researchers have theoreticalize the time travel some how possible I have found some interesting information and articles regarding the the possibility of time travel and enlisting...
  33. S

    I Can light meaningfully travel an infinite distance?

    In particle terms I'm thinking this could be when the signal's photon density drops low enough to be indistinguishable from the vacuum energy. In wave terms, I'm thinking maybe either the amplitude or frequency might drop below any quantum threshold needed to budge an electron shell in any atom...
  34. berkeman

    COVID Options for Travel to China with Chinese-Made Vaccines

    I'm in a tough spot right now, and would appreciate learning about my options. I'm fully vaccinated with the Moderna vaccine, and reasonably good for travel options to most western countries for business trips now (modulo the Delta variant surge and its restrictions). I really need to travel...
  35. elcaro

    Some ideas on interstellar space travel

    Science fiction is of course full of all kind of futuristic ideas about interstellar space travel and ways of propulsion, some more physically plausible then others. But within the current realm of what is physical possible, what could interstellar space travel be like? First you need a source...
  36. J

    I Does a photon travel freely through the CMB photon gas?

    A photon often travels billions of years (Gyr) through the CMB photon gas (410 photons per cubic centimeter) to reach us. Does it travel freely? Let’s share our thoughts about this. For discussion purpose, let’s assume the photon has a wavelength of 500 nm, close to the peak of the solar...
  37. O

    B Untraditional Space Travel

    If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low Earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle. Assuming the launch vehicle...
  38. C

    Ejection speed and travel distance of a ball in a pressurized water pipe

    Diameter of metallic ball : 3.000 inches SG of ball is : 2 ID of pipe is : 4.05 inches ID of seat : 2.885 inches Pressure behind ball when released from seat #1 is 1100 psi Fluid in pipe is Seawater (above and below the ball) Fluid flow rate after ball is released is 800 litres pr minute The...
  39. A

    B Time travel in the quantum world

    hi users, I'm a new member of the forum. My question is about time travel in the quantum world. I am aware of the enormous limitations, but my topic is about individual particles and their ability to travel through time, is that possible for them? My question comes from a speech by an important...
  40. C

    What type of ball can bounce and travel the most?

    From what I have investigated, I know that dimples do a large part of the process of going far, and elasticity for sure is something of the main bounce thing, but things that confuse me like if the ball is empty affects both characteristics, or if the same dimples affect the bounce of the ball...
  41. Limebat

    I Does combusted gas travel faster in a vacuum tube?

    Hey all, So if a gas is combusted, would it travel faster through a vacuum tube or a regular ole' tube? I would assume the vacuum tube, as there are less particulates collisions in the way of the fast-moving gas molecules. Yet this also implies pressure on the outside of the thin barrier _ 2...
  42. MikeandSuch

    How to get away with killing your great grandfather with time travel

    So picture this, its 2500 and you want to time travel back to 2300 to kill your great grandfather, this obviously creates a paradox wherein you prevent yourself from being born right? Well why don't you use your year 2500 technology to create a clone of your grandfather to replace him after (or...
  43. Giovanni Cambria

    A Is this solution for interstellar travel viable?

    I have in mind a way to enable FTL travel. Is this way viable? In the paper: "Weighing the vacuum with the Archimedes experiment" we can see the dependency of the gravitational repulsion exerted by Casimir Vacuum on the energy between the plates. The force goes as E / c^2. In the papers...
  44. S

    B Do photons travel instantaneously?

    Special Relativity tells us - the faster things travel their time is slower relative to a stationary observer. Do massless particles, like photons traveling at the speed of light, experience zero time and in their frame of reference travel "instantaneously".
  45. D

    B Travel Times & Distances: Twin Paradox & Alpha Centauri

    Hi all After reading this thread it got me thinking about the twin paradox, so I looked through some old notes from a module I studied on this subject. According to one of my textbooks, if the traveling twin travels to Alpha Centauri (which is 4.2 light years from Earth) at a speed of 0.9 c...
  46. I

    Using a minimized nuclear reactor for further space travel

    I have been thinking and I thought of a design that may, theoretically result in spacecraft being able to have a self sufficient energy source on board. Here’s my theory, if you have a minimized nuclear reactor (if building something like this is even possible given that the nuclear reaction...
  47. A

    Have anybody considered travel with faster-than-infinite speeds?

    Logically, it seems that if we arrive at the point of destination before we left the point of departure, we have traveled with greater-than-infinite speed. So, I wonder whether anyone introduced faster than infinite speeds in a physical or mathematical theory. Classically, it seems, for travel...
  48. J

    I Understanding Relativity: How Moving Objects Experience Near Light Speed Travel

    Light speed is impossible for anything with mass as more and more energy is required with increasing velocity. But this is only to an observer in a different reference frame. To the moving object, in its own reference frame, why would anything change regardless of how close to c it moves?
  49. R

    How Does Space Travel Affect Natural Aging?

    Changes in the body that come from space travel resemble growing older, providing opportunities to perform aging studies on astronauts. https://www.nmn.com/news/how-does-space-travel-affect-natural-aging Any validity to this?
  50. G

    A Can Data Travel Faster Than Light Computation?

    Hi bear with me I have a conundrum I want to ask you. If data traveled many times the speed of light could the results of decrypted cypher message be computed quicker than any system we currently have? For instance if we sent a burst of data at many times the speed of light across the solar...
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