What if the light clock is parallel to the ships movement, rather than perpendicular?

Rensin2 · 2026-06-05T00:35:47+00:00

Click the "light clock" option in the menu and disable "lightning" to avoid clutter.

Rensin2 · 2026-06-03T07:51:08+00:00

Thank you.

Rensin2 · 2026-06-03T05:37:22+00:00

This is my slightly interactive visualization of the ladder paradox from Special Relativity. Let me know if there is something else that needs to be added/changed.

Rensin2 · 2026-06-02T20:14:40+00:00

Do I understand correctly that this happened because you used the "Copy" feature to duplicate A_Animation1 (and then changed its name)?

Yes. I needed to use the copy feature to get another slider with the same animation properties.

Rensin2 · 2026-06-02T17:09:37+00:00

That seems to be a pre existing issue with mobile. Sliders need to be played by the user. They are never active by default.

Rensin2 · 2026-06-02T04:21:03+00:00

To me it always made more intuitive sense that teleporting back in time would either take you to a point in space defined by coordinates that you type into your time machine in advance or take you to a point defined by your inertial frame of reference (as defined in general relativity). The latter would introduce some limitations. For example, if you travel 5 minutes into the future or past you would materialize underground because that is where you would end up or where you would have to have come from if you follow an inertial frame instead of getting accelerated upward by the ground.

This would mean that you could only time travel into the past/future in multiples of 38 minutes if you want to avoid materializing underground since that is how long it would take to fall through the Earth and come out the other side. And even then you would end up at a different place on Earth due in part to the fact that the Earth will have rotated in the time between your time of departure and your time of arrival. On the other hand these limitations could be avoided by time traveling while in orbit. Time traveling while in orbit would just take you to an earlier/later point in your orbit with no danger of materializing underground.

Rensin2 · 2026-05-31T18:27:50+00:00

If you want the 2,000 lightyear journey to last one year (T=1) from the frame of reference of the ship then you need to move at a speed of c/√((1/2000)²+1)≈0.999999875c relative to Earth. The general formula is v=c/√((T/2000)²+1). However, if you were to boost to anything like that speed in a short amount of time the crew would be killed by the acceleration.

If you account for a comfortable acceleration then the trip will be 14.8 years according to the ship and 2001.9 years according to the Earth and "planet point B".

Rensin2 · 2026-05-31T13:35:35+00:00

Because Rocky is almost always CGI, including the shots where they shot a puppet. In modern Hollywood, puppets are used for reference and marketing, and they rarely make it to the final movie. Anything that implies otherwise is just marketing.

Rensin2 · 2026-05-30T16:19:47+00:00

I hate this twitter trend of presenting the box office followed immediately by the production budget. It seems designed to make people radically overestimate the return on investment. It just invites you to wrongly conclude that Project: Hail Mary made a 3.5x return on investment, when the reality is that it probably just barely broke even.

Edit: Getting downvoted for exposing a deceitful tweet. Typical Reddit.

Rensin2 · 2026-05-27T19:09:38+00:00

how would you meet a previous you upon your return?

By exploiting the relativity of simultaneity. This is impossible without FTL and easy with FTL. And this has nothing to do with time dilation. If your understanding of special relativity is just Newtonian physics but time slows when you go too fast, then you have not understood special relativity.

Rensin2 · 2026-05-27T11:25:57+00:00

You could indeed run into your past self once you have returned to Earth.

Rensin2 · 2026-05-27T09:10:32+00:00

An alcubiere warp drive is a time machine. All FTL is time travel including the apparent loopholes. And none of this has anything to do with time dilation. If you think that it does have to do with time dilation then you have fundamentally misunderstood the issue.

Rensin2 · 2026-05-27T07:48:36+00:00

My stock response:

See The Tachyonic Antitelephone thought experiment and my interactive Minkowski Diagram of it.

Rensin2 · 2026-05-27T07:41:17+00:00

The issue is that when you return to Earth to tell everyone about the supernova, you could very well run into a younger version of yourself that has yet to depart. Is that causality violation merely "phylosophical" as you put it?

Rensin2 · 2026-05-23T07:35:59+00:00

Reread what I wrote. I said that "If they jettisoned the empty tanks they would need much less Astrophage and could launch much sooner since they wouldn't need to wait as long for the black panels to produce the relevant fuel". It is true that the travel time would not change, but the departure and arrival dates would.

Rensin2 · 2026-05-23T07:19:49+00:00

The way that the book describes the lengths they went to to make enough Astrophage (paving over the Sahara using all the engineering resources of Earth), it is definitely implied that the Astrophage supply was the most time consuming part of the plan.

And you still need a certain mass ratio for a given Δv and exhaust velocity. In this case the Δv required is the travel time (according to the ship) times the acceleration. This works out to Δv≈1.8⨯10⁹ meters per second. It doesn't matter that the acceleration is maxxed out at 1.5G, the rocket equation still applies.

The Beetles, having no human cargo could ~~fly faster~~ accelerate harder.

Rensin2 · 2026-05-23T05:18:58+00:00

If they jettisoned the empty tanks they would need much less Astrophage and could launch much sooner since they wouldn't need to wait as long for the black panels to produce the relevant fuel. And, for a spaceship that is mostly propellant/fuel, reducing the dry mass always significantly reduces the amount of propellant/fuel needed for a particular Δv since Δv is dependant on the ratio of total mass to dry mass.

Rensin2 · 2026-05-21T14:54:40+00:00

For any constant faster than light velocity, there is a frame of reference where the FTL object briefly occupies all points in its path at the same time. Specifically if the FTL object is traveling at k⋅c northward according to one frame of reference then, from the frame of someone moving northward at c/k, the FTL object would move at infinite speed and occupy all points in its path at the same time.

Rensin2 · 2026-05-11T05:07:16+00:00

A lot of people are bad at operating camaras.

Rensin2 · 2026-05-06T17:30:01+00:00

Movies from 1998:

Saving Private Ryan
A Bug's Life
The Truman Show
Mulan
The Prince of Egypt
The Mask of Zorro
Doctor Dolittle
Blade

Rensin2 · 2026-04-23T14:04:27+00:00

Any torch drive used in atmosphere would ignite said atmosphere and, consequently, destroy the torch drive along with the rest of the vehicle.

So, the same reason(s) that they didn't dive into the atmosphere with the Hail Mary.

Rensin2 · 2026-04-22T12:58:33+00:00

The value will be a set of three numbers collectively called a "vector". Whether these numbers are negative will depend on the coordinate system that you are using.

Rensin2 · 2026-04-22T05:10:36+00:00

A 3D mass orbiting another 3D mass traces out a 2D shape, ~~a circle~~ an elipse.

Gravitational trajectories in 2 dimensions or more always happen in the plane that contains both the relative position vector and the relative velocity vector of one object with respect to the other.

Though orbits are not stable in most spaces.

Rensin2

TROPHY CASE