Eli5. A question trying to understand if you would see events on a planet happening faster if you moved towards it

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If a planet was 5 million light years away from earth, the James Webb from earth would see it as it was 5 million years ago.

And say if we continued to watch this planet from the earth we would see events happening at the same speed on earth.

if I was to fly towards this planet in a space ship with a telescope, would I see events on the planet being sped up and if I was to fly away would events happen in slow motion?

In: Physics

6 Answers

Anonymous 0 Comments

> if I was to fly towards this planet in a space ship with a telescope, would I see events on the planet being sped up and if I was to fly away would events happen in slow motion?

Effectively, yes. This is an example of the [doppler effect](https://en.wikipedia.org/wiki/Doppler_effect) which you can observe here on Earth with sound waves.

An important thing to note is that this is not the same thing as time dilation. Sometimes people get these two things confused, but they’re completely separate effects.

Anonymous 0 Comments

Yes, but the amount of the change would potentially be small under realistic conditions. Simplying a ton of other physics stuff that would make it much more complicated as to just play conceptually with light traveling over time:

If you somehow traveled the speed of light, you would “see” 2 years in the span of 1 year moving towards it.

Meanwhile, if you moved away such that you covered 1 light year of distance in 1 year plus 1 second, you would “see” 1 second of that distant location play out over a year.

However likely no person would ever approach light speed, the light you would see would be shifted/altered, and all kinds of other stuff comes into play. In realistic scenarios where you move at tiny tiny fractions of light speed, you might see things indeed moving slightly faster, but not to a level you’re likely to percieve.

Anonymous 0 Comments

you would due to the dopler effect. but you also get time dillation. as you move relative to an object, its time appears to change. you have to be moving very fast to notice though

here is a good video series on relativity https://youtube.com/playlist?list=PLoaVOjvkzQtyjhV55wZcdicAz5KexgKvm

Anonymous 0 Comments

No, because the speed of light isn’t actually just the speed of light, it’s the speed of causality.

Imagine you have a book whose words are printed immediately as you turn the page. Pretend you can’t flip the page until you are done reading.

The words are information or matter/energy. The pages are the observable universe. Flipping the page is the amount of time it takes for light/information to travel.

You can’t read the book faster than you can flip the page, because (to simplify/ignore the quirks of quantum physics) information cannot be obtained faster than the speed of light.

Observable phenomena rely on light to be observable. The speed of light is basically the speed of information, and is finite. Tying back to the analogy: you can’t read the book faster than you can flip the pages.

To add to this: nothing in the universe is still. This is where relativity comes in to play. Your speed is relative to your frame of reference. We are constantly moving at tremendous speeds— towards and away— from observable celestial bodies/groups. Do we still see things that appear to be happening faster than they should? No, we see them happening in “real-time” with the limit always being the speed of light itself.

Anonymous 0 Comments

Ha! And I’ve been wondering about basically the reverse all week.

Just reading some scifi where a giant object disappears from a solar system. But for whatever reasons our protagonists dont get to see it happen. Even tho their ship was basically right beside it.

So they jump their FTL ship a few light-hours away and then they can watch the disappearance happen.

And I’ve been wondering if that would work all week lol.

Anonymous 0 Comments

nailed it with your assumption but also youd need to move really really fast to make any measurable difference due to the speed at which light travels