*** Are We All Nuts? ***

Nice! When did you visit? That photo was taken from the inside of Gemini North on Mauna Kea. Been living in Hawaii as an astronomer for just over a decade now.

You know, as you get older, which I am to some degree, the designations of "nuts" or any medical diagnosis or abilities when young becoming increasingly unimportant. They all get blended into your life experience, and interests and abilities change. Perhaps the star athlete from high school now raises wiener dogs and you are now the best of friends due to your same interest, even though he laughed at your inability to throw a basketball.

I try to look at people in a wider perspective and find that everyone has "quirks".

Lets make it easy. We need light to see an object. Light has a finite speed of ~ 186000 miles per second. Same as electricity. Say for example you had a light switch and the wires went 186000 miles before it reached the light (lets take out resistance ), it would take 1 second from the time you flipped the switch till the light turned on, if the wire was 372000 miles long, it would take 2 seconds, 930000 mile long> 5 seconds....

Its the same with stars and planets. The planets are actually relatively close so the time distance isn't days, but it is hours. For example the signal from New Horizons (the space probe that explored Pluto) took over 4 hours to get to Earth. So we see Pluto as it looked 4 hours ago.




Looking at stars is like looking at the past. Our Milky Way galaxy is only 100000 light years long, so we wouldn't see any stars from 250000 light years away. In a non light pollutted sky the most distant star you see is about 4000 light years away. In a suburban sky most stars you see are close or big, the farthest star you can generally see is Deneb at about 2600 light years away, but Deneb is a hypergiant (larger than the distance to Mars), in a really dark sky you can see V762 Cassiopeiae at about 10000 light years away. So what it looked like 10000 years ago.

To really blow your mind, in a dark location Andromeda the nearest large galaxy to us is about 2 million light years away so we see it the way it looked 2 million years ago.

Space is really really really big. This was a picture I took of Andromeda (this is what it looked 2 million years ago). It has 2 dwarf galaxies orbiting it.

Excellent synopsis hfjacinto!

So hypothetically, if I could sit on the head of a beam of light on my flashlight, turn that flashlight on and off for one second, me and that beam of light could travel around the earth 6 or 7 times in one second, correct?

Okay, I gotta digest that a minute.

Now we are getting into relativity, so this gets weird.

Some basic concepts (all have been proven correct).
1) The speed of light is the ultimate barrier, nothing can travel faster (there has been proposed that faster than light particles exist called Tachyons, but there is no evidence they exist)
2) The faster an object goes the more its mass
3) The faster an object goes the slower time gets.
4) The faster an object goes the more energy it needs

This is where we get E=MC^2. What this states is that the Energy = Mass times the speed of light squared. This may sound weird but everything from GPS to Nuclear Energy all rely on the above formula.

Now using the above lets get to your example but lets change it up.

If tried to reach the speed of light with your current mass you would need infinite energy so thats impossible. So lets say that you are massless particle with all your current knowledge and experiences, in essence you but no physical body.

You are launched from Earth. Since you are traveling at the speed of light and since time slows down, the faster you travel the more time slows, till at ~186K MPH time stops. So now you traveled 1 light hour. You stop and look back and you are shocked to see Earth looks exactly like it did an hour ago. Because why Earth has rotated for 1 hour, you can only see it like it looked an hour ago, but to you since time stopped, you haven't aged an hour.

Lets make this even longer. Its the year 2000. You are a 50 year old, you get on your light ship and travel 50 years. You are still 50 years old and if you could look on Earth, it would look like it was in the year 2000. You are still 50 years old, but you also traveled 50 light years from where you started.

At the 50 light year distance, there is a mirror that will reflect you back to Earth. So now you travel 50 years to the mirror, bounce back and travel 50 years back to Earth. Since you never aged, you are still 50. Earth is now in the year 2100, your friends are all dead and you are in the future. If you used a telescope and looked at the light path, you would see Earth the way it looked 100 years ago.

So we could in effect travel to the future, there just isn't a way to go back though.Hope I didn't blow your mind

The faster one can travel the less you can see behind them. At 50% the speed of the light the stars would red/blue shift depending on where they are (receding or getting closer to you). As you are moving so fast there is a cone of darkness behind you. The faster you go the larger the cone of darkness. Till at the speed of light its pure darkness, there is no light to see.

Wow there's a veritable physics lesson going on here, cool lol.

I'll just add that everything hfjacinto said regarding special relativity is based on only 2 assumptions:

1) The speed of light is finite, and the same for any (inertial*) reference frame. Translation: No matter how fast you're moving the speed of light is always constant. So you can never go just a tad slower than c and "see" the light going ahead slightly faster.
2) All physical laws are the same for all observers/inertial reference frames.

Note that invariance of time wasn't an assumption, as Newton had thought! Which gives rise to a lot of interesting phenomena/paradoxes most of which have been verified experimentally.

*inertial just means you're not accelerating = not changing your speed or direction.