deltin9

:snooze: I was studying as usual when my little brother came by, he's 7, we always talk about science and yesterday we started discussing about speed and time, he got really excited and started naming objects and what have you, that can move with the respect of time but then we came to a dead end when he named “LIGHT�?, now I told him light travels fast too just like anything else does and I gave him details. As we all know basically light travels at a speed of 299,792,000 meters per sec depending on what it’s traveling through, and I also told him that light is a part of the electromag spec and it has a wave length that our eyes can see and also you can use light to calculate distance. He asked how far is the sun I told him approximately 8 or 9 light minutes away. Now this is where it gets rough. He’s thinking of light as an object, given the fact that we have the ability to see it so therefore if we see it we are not seeing objects at present time which make absolutely no sense at all but after thinking about what he said I asked couple of my friends and I began to think that I’m losing this debate with him and I came up with some questions my self:snooze:

We do see light from the sun and from many other heavenly bodies but let say for example light from the sun travel 8 light minutes to get to earth does that mean we wait 8 minutes before we see the sun for what it really looks like and I know most people are going to say yes unless you’re use some sort of telescope, but if the answer is yes what about further from the sun. A huge one that my friends and me are discussing is supernova 1987. If scientist said it happened 1987 and our distance is about 190,000 light years away this means it happened 190,000 years before 1987 but we saw it on 1987 if the answer is know please explain. Keep in mind the speed of light is constant and it’s not the fastest thing. :huh:

EricK

We do see the sun as it was 8 minutes ago, and there is no sort of telescope which can let us see now how it was, say, 4 minutes ago. The supernova did happen 190,000 years ago. The light form it only reached us in 1987 because the speed of light is finite and the supernova was a very long way away (190,000 light years away to be exact!).

Eric

ex-xian

Yeah, what EricK said. The supernova that we saw in 1987 actually blew up 190,000 years ago. In fact, I think that most of the star we "see" in the sky no longer exist. They've already went through their life cycles in the time it took for their light to reach us.

Also, the speed of light is constant and it is the fastest thing.

ETA: This might be better in S&S.

Chris Porter

You will get better responses in the Science and Skepticism forum, so I'm moving this thread.

Jesse

That wouldn't be true of stars we can see with the naked eye--we can only see stars in our local region of the galaxy, and the galaxy itself is only about a hundred thousand light years across, while even the shortest-lived stars have life spans of 100 million years or so. You can also see the Andromeda galaxy with the naked eye, it's about 2.5 million light years away, but you can't see any individual stars in it.

IanC

It is the fastest thing!

Check this out:http://www.nasa.gov/vision/universe/...t_cluster.html

This is a picture of something as it was 9 billion years ago. Theres some pictures of something 13 billion ago, I'm sure, I'll try and find it.

Edit:
Got one!
http://observe.arc.nasa.gov/nasa/oot.../ob970917.html The red arc is from 13 billion years ago

Ian

Loren Pechtel

No--light crosses the galaxy in far less than the normal lifespan of even a big star.

DBT

"The life cycle of a star depends upon its mass. High mass stars are much brighter than low mass stars, thus they rapidly burn through their supply of hydrogen fuel. A star like the Sun has enough fuel in its core to burn at its current brightness for approximately 9 billion years. A star that is twice as massive as the Sun will burn through its fuel supply in only 800 million years. A 10 solar mass star, a star that is 10 times more massive than the Sun, burns nearly a thousand times brighter and has only a 20 million year fuel supply. Conversely, a star that is half as massive as the Sun burns slowly enough for its fuel to last more than 20 billion years."

deltin9

Hmmm,
If Einstein was alive today he will swallow back his words. If I’m not mistaking, what I understood from him was that “nothing in the universe can exceed the velocity of light�?.
Well some gases out there do reach and exceed the speed of light.

I’ll get a link to some site later on.


OH,
So we all agree supernova 1987 did not happen 1987?

TNorthover

That's a part of it. But it's a fairly small part of relativity, which has a huge geometric structure, confirmed (as better than what was around before) repeatedly in the last 100 years.

I think that's unlikely (assuming you mean speed of light in a vacuum). Relativity does allow for some slightly strange things comparing speed at two different points, which if you're not careful could lead you to think something was going faster than light.

But what's really claimed is that at a point any body with mass will travel slower than light (i.e. if you get an actual photon to the same point in spacetime, travelling in the same direction, it will go past this object).

I think I'd have heard if gases going at the local speed of light had been found; but if you know more recent information, I'd be interested to hear it.