I’m watching a video here on Vimeo at the moment. It’s called Riding Light and it puts you as it were on a spaceship traveling at light speed. You have a view from the rear window of the ship as it leaves the Sun and begins its voyage outwards. The video is in real time so after you’ve watched for a couple of minutes as the Sun gradually lessens in the viewport suddenly you see Mercury zoom past, a couple of minutes later Venus, etc. I’ve pause the video between Venus and Earth, due up in another few minutes, to ask a question.
The maker of the video admits that he’s taken liberties with certain things like the alignment of planets and asteroids, as well as ignoring the laws of relativity concerning what a photon actually “sees” or how time is experienced at the speed of light. My question is what would one actually see from the rear viewport of such a ship, taking the laws of relativity into account?
But for argument’s sake, let’s say you’re on a ship that is traveling at 0.9999… of the speed of light.
You would “see” basically nothing from the back of the ship, because the light that is reaching you has dopplered far into low frequencies and you cannot see in infrared (well, VERY infrared). The photons will probably have such low energies that even good instruments won’t be able to “see” them.
And depending on how many 9s there are in that number above, from your perspective you probably will reach the heat death stage of the universe almost immediately. There will be nothing out there left to “see”.
You’re right, I way misunderestimated. Heat death is supposed to be in about 10^100 years. That very fast particle you mentioned would have to travel, in its reference frame, for a VERY long time (~10^90 years) to see the heat death of the universe.
But that’s the “final” heat death. I guess the “virtual” heat death (where there will still be almost nothing to see) will be a lot sooner.
To the OP’s question I forgot to include the length contraction when going near light speed. As you move more quickly length contracts along the line of travel. The distance from A <–> B literally gets shorter as measured by the moving person (which combines with time dilation to reduce your perceived travel time).
If you traveled at light speed the universe would be infinitely thin (there would be no distance between A & B). Since we cannot go that fast we never get to zero distance but the length contraction is dramatic:
Object Rest Frame Thickness Particle Frame Thickness
Earth's diameter 12,756 km 0.0399 mm
Solar system 80 AU 37 metres
Sun/Alpha Centauri 4.3 light years 127 km (79 miles)
Milky Way galaxy 30 kiloparsecs 2,895,000 km (about ten times the distance from the Earth to the Moon)
From our perspective a photon can be created and takes a finite time to traverse some distance. We can measure it crossing a room. We can even photograph light moving from A <–> B (MIT has a one trillion frame per second camera that can see light move).
We can see light crossing a room in finite time but from the photon’s perspective is pops into and out of existence instantly and travels nowhere (or across the universe in zero time).
Not only this, but the aberration of light would also greatly distort your field of vision. Imagine your spaceship accelerating steadily. As you approach c, you would see objects at your sides and even behind you gradually move in front of you and concentrate into an incredibly dense cluster right ahead of you!
That just blew my mind! How can anyone ever get their heads around such concepts? I’m guessing that the higher math works as a sort of shield against such seeming insanity, the elegance and precision of the equations acting as stabilizers. Alas, I don’t have such bulwarks against quantum madness!
Well, you can work out the non-relativistic part pretty easily, just with a pencil and a compass (the concentric circles representing the wawefronts of light from a still-standing source). And the direction of light is always perpendicular to the tangent of the wavefront.
I got the following from an old Scientific American, but if I’m recalling it wrongly, please straighten me out (I wouldn’t mind be straitened also.)
A Uranium nucleus, moving at state-of-the-art particle accelerator speeds is essentially a circle, not a sphere. Let’s say it impacts another Uranium atom, which is not moving (from our point of view.) The time it takes the moving one to pass through the stationary one is less than the time it takes for the nucleons to interact.
They’re actually past each other before they realize they’ve been hit, and thereupon explode spectacularly. There’s something “Warner Brothers” about that.
A lot sooner, indeed: It already happened a very long time ago.
And Trinopus, uranium nuclei are very rarely accelerated up to high speed in accelerators. Most often, the particles used in accelerators are just individual protons, or hydrogen ions if you prefer to call them that. Some accelerators use heavy nuclei instead, but almost any heavy nucleus can be used about equally well: At such energies, the internal energy of (say) uranium are insignificant.
A U atom was the example Scientific American gave. Agreed that the internal energy is insignificant. The part I was not sure of was – do two U nuclei, under lab acceleration, pass through each other more swiftly than the time it takes the two to interact with each other.
(i.e., is the time it takes for them to pass each other less than the time it takes for them to start interacting and exploding from the collision? Does this even make sense? This was how SA described it.)
(Solely for purposes of visualization, imagine a bullet made of impact-detonating explosive, which you fire at a very thin metal target…at insanely high speed. The time it takes for the bullet to pass through the target is much less than the time it takes the chemical explosive to detonate, so it goes off “behind” the target.)
You’ll have to take it up with MIT if they are playing a bit fast and loose with the terminology and what they are actually achieving here. I just posted the title as they gave it.
As I understand it, picophotography isn’t taking many images of the same pulse of light; it’s taking images of many different identical pulses of light, at different points in their propagations. So if you have an identical pulse every 1000 picoseconds, and you take one picture every 1010 picoseconds, it’ll look the same as if you took one picture every 10 picoseconds.
This is all waaay past my knowledge but if it helps the video I linked to said they used 500 cameras (or rather sensors…he mentions it at around 0:26 in the linked video) and timed each camera to take a picture at incredibly small intervals from the one before it (so they went off in rapid-fire sequence). Then they knit all the pics together.
Certainly no single earthly camera could take pics that fast.