Space/Time Travel

Would that work, you ask. I dunno, but it is thought provoking!

There is a bit of misunderstanding going on here, though. You see, Warp Factor 10 (per the Star Trek canon) is not ten times the speed of light, it is (approx) 1,000 times the speed of light.

Star Trek (Original Series) was, after all, one hour episodes.

Its no secret that time travel does exist, just not in the exciting way you want it to. If you were traveling at the speed of light for the entire trip for 12 years to another planet it would seem like no time passed at all. Then you return to earth at the speed of light another 12 year trip. Since this is all hypothetical lets assume you could get to the speed of light and decelerate very quickly. The problem would be when you returned to earth, 24 years would have passed for everyone else while the trip would have been quick to you. You would have basically been standing still in time as compared to earth time, congrats you made it to the future. That counts as time travel

You don't have to exceed the speed of light. As you go close to the speed of light, your time slows down. What would be a year for you might be five years to someone at home on earth.

If you are moving at close to the speed of light with respect to the earth, the earth is moving at close to the speed of light with respect to you. Length in the direction of motion of a moving object is shortened, so for you, the distance to distant stars is shortened.

The ratio of time slowing and length shortening is given by the formula:

R = sqrt(1-(v/c)²), where v is your velocity and c is the velocity of light

So, if your speed gives a factor of 5 and you are travelling to a star 5 light years away, it would seem to you that the star was only 1 light year away. To someone on earth, it would seem to take 5 years and your time in the spaceship slowed down by a factor of 5.

This video probably explains it better...

Here is an example of time dilation and Lorentz contraction.

Muons are subatomic particles created in the upper atmosphere by cosmic rays. A muon in captivity lasts for about 1 microsecond before decaying. If it were traveling at close to the speed of light, it could only travel about 1000 feet.

But muons make it to the earth's surface, much farther than 1000 feet. How could that be?

The muon is traveling close to the speed of light so for it, time slows way down. From the muon's point of view, the earth is moving close to the speed of light, so the depth of the atmosphere is foreshortened, and it doesn't have far to go.

https://en.wikipedia.org/wiki/Experimental_testing_of_time_dilation

Speed is only part of the problem.

It’s the effects of weightlessness on the body during the trip.

Speed is only part of the problem.

It’s the effects of weightlessness on the body during the trip.

Perhaps you can create your own gravity, or go old-school and simply spin your spacecraft.

Perhaps,...

Ignoring relativistic effects, if the ship accelerates at g, that simulates gravity for the crew, and doing it for 1 year gets close to the speed of light. Then you can go as far as you like before decelerating at g.

Of course the problem is providing the thrust to give g for a year. And Earth has still aged more than the crew, when they return.

They might find this . . .

What is the acceleration to simulate 1G

9.8 m*s^-2. That's g, acceleration due to gravity on surface of Earth. G is the gravitational constant, 6.6743×10⁻¹¹ m³ kg⁻¹ s⁻².

This is above my skill.

I’m following this I think…, I like know what accelerated speed do you need on a space ship to hold a constant 1 G Until you hit speed of light, does this formula say that?

This would some what go back to Newton on the acceleration of the fall of an Apple from when it releases itself from the branch until it hits the ground…

See codemasters first reply:-

First stop confusing g with G

G is a constant used to calculate the gravitational force between two masses in space:-

force = GM₁M₂/r²

g is the acceleration due to gravity on earth approximately 10 m/s²

In order to simulate that gravity on a rocket, you would need to accelerate that rocket at:- g

Newton's apple falls down with an acceleration of ~1 lyr per yr². If you need more convincing arguments, I will be happy to expand on the above.

I appreciate the offer, like I mentioned earlier, this is above my skill-set. but that doesn't mean I'm not interested. I'd rather look through what's been given to me first and go through it first, to get a better understanding on this.

"Perhaps you can create your own gravity, or go old-school and simply spin your spacecraft."

Perhaps, if we can get nuclear fusion rocket propulsion optimized,^[1] you can get there fast and have some gravity along the way as a bonus.

Ideally, you want to accelerate at 1g for half the distance and decelerate at 1g for the remainder. At 1g, it takes about a year to accelerate to near the speed of light, so one can go very far without aging very much.

[1] Sabine Hossenfelder sounds optimistic: https://www.youtube.com/watch?v=vIp_jwHMjIk

I beat you to that by 1 minute Jorrie

Codemaster wrote: "Ignoring relativistic effects, if the ship accelerates at g, that simulates gravity for the crew, and doing it for 1 year gets close to the speed of light. Then you can go as far as you like before decelerating at g."

If we include relativistic effects, it takes quite a bit longer than 1 year to get close to c (with a 1g proper acceleration as measured by an accelerometer on the spacecraft). The reason is that the coordinate acceleration, as measured from Earth, will be gradually decreasing.

I worked out a scenario for getting to the proximity of Proxima Centauri, by doing 1g for half the time and -1g for the second half. It took 3.5 years of spacecraft time to get there, compared to 5.6 years Earth time. At the halfway point, the craft reaches a speed of 0.94c relative to Earth.

Jorrie, can you tell us: Does the vessel need sufficient fuel for 3.5 year burn, or 5.6 year burn (outbound trip only)?

This depends on point of view, so restated: how much fuel does the vessel load at start of a one-way trip?

No, you do not need to burn fuel all the time. That was just to get there faster, plus to enjoy some 'Earthly' gravity all the time.

I accept that no foreseeable technology will allow propulsion at 1g acceleration for such a long time. Even for (future) nuclear fusion drives, the amount of fuel required will be immense, but not impossible.

We may have to relax the 1g requirement and adapt to a more Mars-like 0.38g to save fuel. Or maybe we can adapt to 0.165g, which is the Moon's surface gravity. I will post some calculations when time allows.

I found the answer in https://math.ucr.edu/home/baez/physics/Relativity/SR/Rocket/rocket.html, worked out for a 100% efficient propulsion, meaning it converts all of the fuel-mass to energy, i.e. E=mc². This will require matter-antimatter annihilation, so we can forget about it for the foreseeable future.

The masses shown are per kg of payload. Suppose we can get an efficiency of 1% by means of nuclear fusion, meaning you need to multiply the above by 100. For Proxima Centauri, this requires 4 tonnes of fuel for every kg of payload.

A potential propulsion system fuses Deuterium and Helium-3, generating electricity and lots of protons, which can then be electromagnetically accelerated out of the rocket tailpipe. There will obviously be multiple issues to be solved...

I accept that no foreseeable technology will allow propulsion at 1g acceleration for such a long time.

Clearly, carrying your fuel with you is terribly inefficient. Maybe a Bussard ramjet could be made to work.

https://en.wikipedia.org/wiki/Bussard_ramjet

"Clearly, carrying your fuel with you is terribly inefficient. Maybe a Bussard ramjet could be made to work."

I like it. Maybe the "Ram Augmented Interstellar Rocket (RAIR)" will be even more practical?

Thanks for the details, interesting

Better still: assuming you have bottomless reserves of power. Either grab or make a lump of neutron star; contain it (also impossible with current technology) at the front end of your space ship; gradually move closer to it while increasing the acceleration of the whole ship. When the whole ship is accelerating at ng and you are close enough to the mass to provide a gravity of (n-1)g or (n+1)g you will experience normal gravity. In between are areas of low gravity, and there are other off axis points where it's one g, but, beware you'll need Escher to design the "stairs".

Like other constant acceleration ships you have to flip the whole thing at half way to your destination and decelerate for the second half of the journey, there is no way to get on or off at "bus stops" along the route.

Hey Jorrie, since I can see you're into all this I'll ask you a little question.

Let's make an assumption for a moment we have "solved" the problem of fuel energy/mass density issue for propulsion use, ie we can energywise for example accelerate at 1g felt by the astronauts for 0.97 years which is the time it would take to reach C, leaving relativity out, time in that spaceship will from our perspective, being out of it, slow down of course, but the astronauts will perceive time passing normally, same thing applying for the spaceship engines (and their fuel consumption), no? I.e. the C limitation doesn't seem to apply to them, no matter how a third party out of their reference system sees it. Where's the catch?

Spoiler: There's no catch. S.M.

"... but the astronauts will perceive time passing normally, same thing applying for the spaceship engines (and their fuel consumption), no? I.e. the C limitation doesn't seem to apply to them, no matter how a third party out of their reference system sees it. Where's the catch?"

Spoiler: You are right, but there may be a catch!

The principle of equivalence between acceleration and gravity says that there is no internally observable difference between the ship being accelerated at 1g and one sitting at rest on the surface of Earth. Or to make it even more equivalent, say we tether the ship to earth and let its propulsion keep the (short) tether just taught.
Only by looking out of a window (or otherwise observing the outside world) will the occupants discover that they are not going anywhere. Likewise, the astronauts on their way to Proxima Centauri will not be able to internally detect their motion. They will have to look out of the window to see the image of Earth shrinking fast and the target star looming brighter and brighter.

Let us assume that they can detect when they are halfway, by means of scaling the images and by triangulation with other nearby stars. They find that they have travelled 2.125 lightyears, and they can directly read their local travel time as 1.44 years (remember that their clocks record less elapsed time than on Earth). This means that the ship’s average speed has been nearly 50% faster than light! How can that be?

The problem lies with a mix of coordinate systems. They use Earth-based distances, but ship-based time (propertime). This result in what is called space-propertime, not spacetime. The average speed that they have measured is called proper-velocity, which does not have a speed limit – it can theoretically go to infinity.

The ‘catch’ has to do with mixing coordinates and with mixing Newtonian dynamics with Einstein dynamics.

You said “Every star light has a different velocity. Only local light is constant.”

I’m not sure… If, uhhhh… This doesn’t really sound correct… So, just how local is light, and what happens to local light after this distance is exceeded…

Every star… the light from….

I don’t know what to do with this part.

I don’t believe it’s really understood and how I understand it, it’s all relative.

The velocity is the same, it’s the wave length that changes what’s as known as the Doppler effectwhich describes the change in frequency of a wave of light as observed by an observer moving relative to the wave's source, causing a blueshift (higher frequency) when approaching and a redshift (lower frequency) when receding.

We start out journey at 10% the speed of light. But then jump ahead in time by 120 years.

"Jumping ahead" can basically be accomplished by cryonics if the time travel thing doesn't work out.

https://en.wikipedia.org/wiki/Cryonics#:~:text=The%20first%20body%20to%20be,)%20on%20January%2012%2C%201967.

Dreaming/hallucinating: There are such things as "entangled" particles, theoreticians say, and changes are instantaneous at a distance. Could a spaceship be "entangled?" Thus Warp drive???

The problem with that is you have to place one of the entangled particle(s) at the destination first. So perhaps leap frogging from one distant place to another would eventually get there, with a repeater at each point. This could eventually establish a network for no-delay communication.

The first ship to depart will not be the first to arrive, because successive generations of technology will be faster and catch up to the one ahead.

Add that to the fact that genetics will advance to the point that aging will not occur and there will be no need for hibernating on long trips.

"Imagine that the universe, and everything in it, even beyond the observable universe was created instantaneously, in NO TIME AT ALL, because time did not exist in the beginning."

In a way, this is the prevailing Big bang theory. Everything starts out as pure energy and part of that energy is (slowly) converted into the matter that we (partially) observe today.

On the issue of space and time as an illusion, the jury is still out. We surely experience distance and time, iilusion or not.

IMHO:

Everything starts with a photon. Even a chemical explosion begins with a single photon.

"Let there be light"

Before the first photon, there was a true "Void", the total absence of anything, and darkness which is not the same as empty "space". There is no total void now; Only before the beginning, the first photon.

The deep void was featureless and truly empty, which is why our physics break down close to, but not at the singularity.

... about 90% of this discussion is over my head but I get the feeling our being linked to Sol' gravity has warped our perception of speed , not to mention our interpretation of time.

Fascinating, still.

Skies.

J

IF, and that is a big IF, the current info from UFO sightings are true, then inertia has been overcome by technology making instant stops, starts, and turns possible.

And if that technology is ever possible, so would exceeding C be possible.

The universe is very old. Humans have existed only for a blink in the history of the universe. It is very unlikely that were the first and most advanced civilization.

And insofar as a peaceful civilization being the only type to survive, I say look at nature... only the strongest survive.

I agree with Carl Sagan, I do not think it wise to advertise our presence and location to the universe at large.

The friendly skies may not be all that friendly after all.

NSS, I regret that once again I must drive this home.

I'm sorry to have to give you this bad news but I have just returned from the future (211 years hence) where a time machine made with some rudimentary circuitry for the time, was tested and sadly incinerated upon reintegration. The sole occupant of the craft was no more than a cinder and ID through DNA was impossible to determine.

Thus, although I could provide you with all of the necessary information for your quest, my duty as a lesser Time Lord prevents me from harming, allowing harm of or facilitating harm to less advanced life forms.

Please trust me my friend, it's for your own good that you immediately cease pondering production of these types of craft for 124 years, after which time your race will be expected to have the ability to traverse time and space effortlessly.

Perhaps you should try your hand at creating great video games (I have inside information that you would be a success in that industry).

Good luck in your future endeavors!

So…

Sounds like a ‘No’ vote on the FLS stuff from Haymaker.

But why do you want to go at a speed ? The Intrastellar travel is supposed to eb at Zero speed (at least that's what all SF's tell) - you enter a Space-Time Singularity and get out of it wherever you want - without any time loss. Only problem is to create the singularity 'Tube' the way you want it to be ie from Earth at one end and Alpha Centauri on other.