The thrust of curiosity that leads men to try to go where no one has gone before. (The Space thread)

[Dicknose]

No!
Light travels at c compared to all sources and viewers.
That's the weird bit.

So that light from both would reach earth in 1 year.
The only difference is that the one moving towards us would be frequency shifted (blue shift)

If you asked someone on each of these objects to check the speed of the light leaving them they would agree it was at c.
Get them to check the others light source and again c.

Both would think that the other is moving at 0.5c relative to themselves, which means both would think the other is "half way to c". But they are not, no matter how fast they go, any light is always at c compared to them.

The frequency of the light will change as you change speed. But the speed of light is always c.

[Rare White Ape]

Yep, the only thing that matters in your reference frame... is your reference frame.

An object that is moving toward you appears brighter, because the light that is emitted by that object has more energy (to you), not more speed.

[Rare White Ape]

Now let's say you're the one who is moving. You emit light at c compared to the object you're flying past.

To you, the light you emit is travelling at c, but you're also moving past another object like a galaxy or something at 0.1c. So, to you, you think the light is travelling at your speed, plus the speed of light, which equals 1.1c, amirite?

But from the galaxy's perspective, you're travelling at 0.1c but the light you're emitting is still at c and you look a bit brighter while you approach and dimmer while you move away.

This can't be right, can it? Well what's the answer?

The answer is that time slows down. You might think that light emitted from you is going past the galaxy at higher than c, but in reality time has slowed and it is preserving the cosmic speed limit, so light still moves away from you and past the galaxy at c. You can't perceive this yourself. All you know is that you're travelling at 0.1c and there's a galaxy moving past your window, and clocks on your space ship still run at 1 second per second per second.

But wait a minute! How can you know for sure that you're the one who is moving? What if you're stationary and it's the galaxy that is moving past you?

Well, you would still feel time passing at 1 second per second per second, and you would still see a galaxy passing your window at 0.1c. But what about the time for an observer within the galaxy? You would perceive their time to be passing slower than yours. And the kicker? That's the exact same thing you'd perceive of the galaxy if it was definitely you who was moving.

The key to all of this is what DN said on the previous page: there is no absolute frame of reference.

No observer is the final authority on the flow of time or space. All that should matter to you is your frame of reference.

[Freude am Fahren]

So strange to try and understand.

Like, say there was a planet 10 light years away that is completely stationary in relation to Earth. We develop a craft that can go .6c Let's say for arguments sake, it accelerates to that speed nearly instantaneously. After 10 years, it should be 6/10ths of the way there, moving at .6c. Now, let's say that it dropped a second craft, that also could nearly instantly reach .6c. Logic would say that as observer on that craft in relation to the two planets it travelling at 1.2c. Could that craft reach a planet 10 light years away in less than 10 years? No, right? If you were to Take a snap shot of the planet the moment the craft leaves from planet b, there's no way the craft would reach you before you saw it leave.

[Rare White Ape]

Well, remember that the faster you go, the more energy is required to go faster. It's super simple to accelerate a car from 30 to 60MPH. At normal 2017 human spacecraft speeds like we have now, if you pour more energy into the system it's pretty easy to go twice as fast. You just need a much bigger fuel tank.

But at speeds as fast as 0.6c you'd need a fuel tank the size of Jupiter to go faster.

Say we could drop some sort of futuristic fusion-powered high speed craft of a reasonable size from another high speed craft. Just getting to 0.61c would take a heap of effort, since it is already travelling close to it's limit. There's no way that it would get anywhere near 0.9c unless you found a way to harness all of its stored energy in an instant, but then you'd run out of fuel pretty quickly and you'd have no spacecraft left because it got vapourised.

On to your second point about taking a photo. If you took a shot the actual moment it leaves, you'd have a picture of a stationary spacecraft, because it would be ten years before you observe the spacecraft moving.

But if you took a photo at the moment you saw it moving, for you it would look like it only took four years for it to arrive.

[Rare White Ape]

Here's a bonus for anyone who seems interested:

A few years ago the MIT Game Lab built a game called A Slower Speed of Light. The idea behind it is as you move about the level picking up orbs, the speed of light lowers down to near walking speed. This leads to some trippy-as-hell visuals when relativistic effects come into play. It's free to download and try yourself.

http://gamelab.mit.edu/games/a-slower-speed-of-light/

[Crazed_Insanity]

Trippy indeed!

Hey, maybe certain drugs can slow down speed of light in our brains without using MIT's game engine!

[Freude am Fahren]

Space-X will be Re!-launching a Falcon 9 tonight!

[Dicknose]

Cheap bastards using a second hand rocket!

[Crazed_Insanity]

SpaceX recycling the Falcon9 making it great again!!! Impressive indeed!