A question about light and the distant universe.?

Question

I know quite a bit about space and light, however there is one thing that I have trouble with: How do we know if anything exists if it is so far away? Are we assuming things several million lightyears away still exist? (sorry if this sounds like an ignorant question to some people)

Answer 1

Well, we can only assume, really... we can judge some stars by their type how old they are, and how much longer they probably have left - which means, even though they're very far away, they're *probably* still there.

It's true, though - that some of what we are seeing *now* probably no longer exists. But, at the same time, we talk about the life spans of stars in *billions* of years, when we're seeing them as they were just *million* of years ago - implying that they're probably still there.

Answer 2

Actually, they really is no way of knowing if an object millions of lighyears away still exists. Only when the object changes do we know that something happened way out there. Example; Sandulek -202 - a star in the southern hemisphere is roughly 170,000 lightyears away. In Feb 1987, the light from it's supernova arrived at Earth. There was no way of knowing that this event happened until we were able to observe the event. Actually, a neutrino detector in Japan recorded the blast just moments before the star began brightening. The detector just happened to be up and running when the event took place. There is about a 2 minute interlude every few minutes when the detector is turned off for calibration purposes. If the supernova had happened during that time, we would never have known that SN1987a produced neutrinos prior to the detonation. Also, it took many days after the event before scientists, studying the results, concluded that they had detected the event. The neutrinos only preceeded the photons of light by just a few moments, so I guess in some small way SN1987a could have been seen to be going supernova before the brightening took place, but because of the time it took for the scientists see their results, the supernova had already been discovered by optical astronomers half way around the globe.

I hope this helps. Good luck.

Answer 3

No, we do not assume that things we see today exist like we see them. The light that comes from the far ends of the universe only allows us a look into the distant past. Which is exactly what makes looking "far" so interesting for astronomers: they get to see the whole history of the universe at once! It's just not the same stars and galaxies but different ones at different ages.

What is in the place of these old objects we see today, we can't tell. That's the price we pay for knowing about the past: we can't know the present and we can't know the future.

Hope this helps.

Your question is quite smart, by the way. Science is a lot about knowing what one can not know. This is one of the areas where we can tell very precisely what we don't know and never will know. For a scientist that's worth a lot more than trying to know everything at once. To assume total ignorance and then to enlighten oneself a little bit is part of the mindset of being a scientist. Because if you thought you knew everything, already, you wouldn't have to be curious anymore, right?

Answer 4

not ignorant at all... The only things we know are what the conditions were when the light was created. For distant things, there has been a long time for things to change since the light left those stars. Actually, it is safer to assume that things are not like they were on any particular star if the light has been traveling for many millions of years. We can make some guesses about how things change but we do not know anything about what is happening right now.

Answer 5

Not an 'ignorant' question at all, and you're thinking is sound :: we have absolutely no way of knowing for dead certain that anything n light years away still exists. However, if we're observing some immense galaxy the chances are very good that it still exists 'now,' although it surely has changed in some ways, like distance, configuration, magnitude, etc.,.

Answer 6

Nothing wrong with this question, in fact it's a good one.

All you sense are delayed so we perceive the environment be it the keyboard I'm typing on or a distant galaxy, in the past. We have no way to telling of telling it anything is real.

Interesting enough quantumclaustrophobe comment is flawed. What we see in a galaxy is the short lived high mass stars, not the low mass stars that live billions of years so a galaxy could change dramatically in a few billion years.

Answer 7

The answer is very simple.
A number of stars will have disappeared, due to supernova events. We know this is a small number because we dont see supernovae every day, and there are billions and billions of stars remaining.
If stars were rapidly changing, we would see stars in a different state, the more faint they were. The main difference is only something called their red shift value.
We thus know that its all changing very very slowly, just by looking, and therefore what we see, although delayed, still exists.

Answer 8

An interesting question, but as everything we observe is based either on light or radiation sources then presumably the further away it is then the less likely it is to still exist....particularly for older stars and other objects. Less likely maybe that whole galaxies would have been wiped out...but then again who knows

Answer 9

It takes 1 second for light to travel 300.000 kilometres.
One light year is....hm mm 300 000 km times the second there are in a year. And several million light years takes 300 000 km times "several million light years in seconds".
A distance we can´t even imagine. So what you see now is what happened 300000 km times several million light years in seconds as the light hits your eye just at that time.
Pugh! Imagine....? I don´t think anybody can.

Answer 10

No we are not assuming that they exist. We know that they could be gone,because the light is still traveling through space. Who is saying that they still exist? although they probably do,we cannot say so for sure