# If you travel through space at lightspeed, will the stars in the background appear to move relatively slow?September 20, 2007 6:50 PM   Subscribe

If you travel through space at lightspeed, will the stars in the background appear to move relatively slow?

I am watching The Fountain (after the FPP about it the other day) and I noticed while traveling through space, the background of stars "moves" fairly slow. Wouldn't Hugh Jackman and his tree have to be traveling at lightspeed to get to his destination within a lifetime?

Or is it more like Star Trek / Star Wars where everything becomes a streak? (I think in Star Trek warp speeds are faster than light.)

So, let's say we're traveling at lightspeed from Earth to Vega (like in Contact), a total of 24.3 light years away, will the stars in the background appear to move relatively slow?

Also, will going any slower change the "speed" of the passing stars?
posted by paulinsanjuan to Science & Nature (16 answers total) 5 users marked this as a favorite

If it takes 24.3 years, and most of the stuff is way farther away then no, you won't expect to see streaks, and most of the stars will not appear to move.
posted by furtive at 6:56 PM on September 20, 2007

If you travel at the speed of light, you wouldn't see anything outside. From the point of view of the object traveling, the journey would be instantaneous. Time passes slower and slower when you accelerate toward the speed of light and doesn't move at all when you reach it.
posted by McSly at 6:57 PM on September 20, 2007

A parsec (~3.2 light years) is a parallax second; it's the distance at which an object must be from the earth such that from once side of earth's orbit to the other angle of parallax is one second.

The breadth of earth's orbid is 16 light minutes, so that's how long it will take stuff that's 1 parsec away to shift by 1 second through your field of view. Most stuff you see in the sky is much farther away than one parsec, and will have a much smaller effect of rotation.

For comparison, the sun travels through the sky at the rate of 1 second of arc every 15 seconds of time (360 degrees over 24 hours).
posted by aubilenon at 6:59 PM on September 20, 2007 [1 favorite]

See What would a relativistic interstellar traveller see? for some simulated pictures for what it might look like.

To see stars fly by like in certain sci-fi series, she would have to travel much faster, on the order of light years per experienced ship second. This corresponds to the actual velocity of 0.9999999999999994c, or (1 - 6x10^(-16))c.

And they point out that all stars would appear coming from a tiny point in space and all radiation would be shifted to gamma, so you wouldn't actually see it.
posted by skynxnex at 7:00 PM on September 20, 2007 [2 favorites]

What skynxnex said; for more detailed explanations aimed at the non physicist, try this.

(via...)
posted by Luddite at 7:05 PM on September 20, 2007

I disagree, you could get there, you just have to convert yourself to zero-mass particles first.
posted by blue_beetle at 7:24 PM on September 20, 2007

Well, on Star Trek when they travel at warp speed, they ARE traveling faster than the speed of light.
posted by IndigoRain at 7:25 PM on September 20, 2007

This is what it would look like if you weren't in space according to Carl Sagan.
posted by Redruin at 9:10 PM on September 20, 2007

Previously.
posted by Freaky at 9:45 PM on September 20, 2007

Look at the first link, showing the compression cone ahead of the .99c traveller. As you travel faster in a single direction, it becomes increasingly unlikely for photons approaching you from a wider side angle to reach you. As you accelerated closer to c, the perceivable universe would seem to compress into tighter cones in front of and behind you. Just before you hit c (somehow), your entire rear universe would have shrunk to a point of light which now shifts red-ward and vanishes. Finally, were you to reach c, no photons from behind you could ever actually reach you, and in front of you the entire visible universe would have compressed to a tiny pointlike spot in your direction of travel (I am ignoring blue shifting). Time dilation would have increased to such a degree that not very much at all seems to happen in the universe as you travel through it, or at least, not much happens in its interactions with *you*. For you, time does indeed appear to be standing still... until you hit something. In fact, you would have become a lightbeam, which is pretty much where Einstein began his daydreams about frames of reference.
posted by meehawl at 10:57 PM on September 20, 2007

Wouldn't Hugh Jackman and his tree have to be traveling at lightspeed to get to his destination within a lifetime?

Just answering this part. No. Because of time dilation you don't have to move at light speed to travel multiple hundreds of light years. If you were to accelerate at 1g for a year(your year), then turn your spaceship around and accelerate in the opposite direction for the same amount of time you will be much further than 2 light years from Earth. I don't know the math to tell you how far though.

However someone observing your trip from Earth will see it as taking much longer than 2 years.
posted by Bonzai at 11:54 PM on September 20, 2007

HA! I found a javascript calculator. So I can give you some examples.

All examples are on a spaceship that can accelerate at 1G continuously. All trips accelerate away from the Earth until it reaches the midway point and then turns around and accelerates in the opposite direction (so that it's at relative rest at the end)

Alpha Centuri (4.3 light years away)
Time to people on ship: 3.56 years
Time to observers on earth: 5.96 years
max speed 95%c

Rigel (913 light years away)
Time to people on ship: 13.27 years
Time to observers on earth: 914.9 years
max speed 99.997%c

Center of the Galaxy (30,000 light years away)
Time to people on ship: 20.039 years
Time to observers on earth: 30001.93 years
max speed 99.997%c

Edge of the Universe (150,000,000,000 light years away)
Time to people on ship: 45.47 years
Time to observers on earth: 150,000,000,001.93 years
max speed 1c (almost)
posted by Bonzai at 12:10 AM on September 21, 2007

Also, it should be noted that narrative casts some doubt as to how literally we should consider Tommy's future.
posted by KirkJobSluder at 5:28 AM on September 21, 2007

Response by poster: i dont know which one to mark as best. all of them?
posted by paulinsanjuan at 6:55 AM on September 21, 2007

download Celestia (amazing program btw), and accelerate to light speed. You'll be surprised how slow the background stars move
posted by derbs at 8:42 AM on September 21, 2007

When I watched The Fountain, it was my understanding that Jackman's character was basically immortal at the end, and could therefore take his sweet old time traveling across the galaxy at sub-light speeds, so long as the biosphere kept the Tree of Life (and therefore himself) alive.

Immortality sort of solves the problem of interstellar distance, except for the storage required for an eternity of in-flight magazines.
posted by steef at 11:02 AM on September 21, 2007

« Older How can I print my notes onto 3x5 cards?   |   Social butterfly or talking head? Newer »