4 ms·

Actually that's just flat-out wrong. Light has an absolute speed. It's the only absolute thing in the universe. It's not relative. And -- this comes directly fr

by sabat 16y ago

Actually that's just flat-out wrong. Light has an absolute speed. It's the only absolute thing in the universe. It's not relative. And -- this comes directly from Brian Greene -- the speed of light always looks like the speed of light, no matter how fast you're travelling. The speed of light never looks like 10% of the speed of light. It's always the same -- a constant.

ars 16y ago
I didn't say the speed of light - I said 90% of the speed of light. I was refuting the idea of the speed of light as some sort of master clock. But yes, the actual speed of light always looks like the speed of light.
burgerbrain 16y ago
The speed of light is always 'the speed of light' regardless of your reference frame, however the speed of other objects is purely relative. The 'what' in "So what looks like 90% of the speed of light to you, can look like 10% of the speed of light to someone else." is referring to something travelling slower than the speed of light. A train or bullet perhaps. In different reference frames it can be said that this train/bullet is travelling at different percentages of the speed of light. That's why it gets weird. EDIT: To illustrate this, lets say we're sitting on the earth watching an astronaut. Relative to our position, he is travelling at 1/2 the speed of light. Now, some joker decides to shine his laser pointer at the astronaut. From earth we see the laser beam^ blast past the astronaut at .5c (.5c + .5c = 1c, the speed the laser light is traveling). NOW! from the astronauts perspective! Instead of seeing the laser pass him at .5c, he sees it pass him a nice proper 1c. weird, but it's how the universe works. ^reflecting off spacedust of course :P
- sabat 16y ago
  Thanks for that clarification. But the speed of light can only be measured relative to YOU That's still wrong, though. The speed of light is an absolute; it's not My Speed + the Speed of Light. The person I was who originally responded to me (ars) was trying to say that motion in space is impossible because it's always relative -- apparently even to the speed of light. That's not true; motion is relative to the speed of light, period. And what I had been trying to express (however badly) was that the faster you move relative to the speed of light, the slower you move in time. I think ars was just in a nitpicky mood and was fixating on the particular wording I chose.

by sabat 16y ago

ars 16y ago

I didn't say the speed of light - I said 90% of the speed of light. I was refuting the idea of the speed of light as some sort of master clock. But yes, the actual speed of light always looks like the speed of light.

burgerbrain 16y ago

The speed of light is always 'the speed of light' regardless of your reference frame, however the speed of other objects is purely relative. The 'what' in "So what looks like 90% of the speed of light to you, can look like 10% of the speed of light to someone else." is referring to something travelling slower than the speed of light. A train or bullet perhaps. In different reference frames it can be said that this train/bullet is travelling at different percentages of the speed of light. That's why it gets weird. EDIT: To illustrate this, lets say we're sitting on the earth watching an astronaut. Relative to our position, he is travelling at 1/2 the speed of light. Now, some joker decides to shine his laser pointer at the astronaut. From earth we see the laser beam^ blast past the astronaut at .5c (.5c + .5c = 1c, the speed the laser light is traveling). NOW! from the astronauts perspective! Instead of seeing the laser pass him at .5c, he sees it pass him a nice proper 1c. weird, but it's how the universe works. ^reflecting off spacedust of course :P

sabat 16y ago
Thanks for that clarification. But the speed of light can only be measured relative to YOU That's still wrong, though. The speed of light is an absolute; it's not My Speed + the Speed of Light. The person I was who originally responded to me (ars) was trying to say that motion in space is impossible because it's always relative -- apparently even to the speed of light. That's not true; motion is relative to the speed of light, period. And what I had been trying to express (however badly) was that the faster you move relative to the speed of light, the slower you move in time. I think ars was just in a nitpicky mood and was fixating on the particular wording I chose.