Travel Definition and 994 Threads

I was watching a video from Neil DeGrasse Tyson on time travel. He said you can’t travel back in time to meet yourself. Is this correct or am I misunderstanding this? Explanations would be greatly appreciated. I know it’s only a hypothesis, but I was wondering about the answer in terms of the...

I have heard this before many times, ‘we can’t reach some parts of our universe because of expansion’ but can we launch a massive rocket and then launch a rocket from the first rocket in the same direction and then again and again? Due to relativity.

Since "Space" is just a Distance between 2 objects , isn't "Space" just equal to Distance ? If so , then the term "SpaceTime" can be called DistanceTime . Which I think clarifies what is meant . And I think it's meaning is thus a Distance Time . In other words , it just refers to the TIME it...

Is it at a single point half way between the two stars, or is it in a superposition of locations forming a hemispherical shell around the sun, or does it just not exist at all until it interacts with a particle in Alpha Centauri?

Tommy Lee Jones Contemplates Plank's Constant From the Tokyo Metro. It's common for western celebrities to pose for advertising in Japan. Ringo Starr, Avril Lavigne, Jill and Joe Biden...

Here's a travel blog by a couple from Estonia, who ride their BMW motorcycle 200,000km and to 85 countries around the world. Proper photographs included! https://www.advrider.com/f/threads/from-estonia-with-love-round-the-world.480532/

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

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 •...

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

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...

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??

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?

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

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...

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...

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...

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...

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?

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...

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...

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...

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...

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...

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.

Is time travel possible in Newtonian curved spacetime?

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?

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{...

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 ÷...

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...

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...

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

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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".