Relative perspective

[dabliss74]

ok so ...if half the stars we see in the sky arent there anymore .....if we see the sun 7 minutes from 'real time' ...i have a poser.....this goes along with the whole "we have/are being visited by aliens" deal....say there is a star 13 million light yrs away and there is a planet with intelligent curious life...they look our direction....would they not see a planet inhabited by 'unintelligent' dinosaurs?....heres something else...if we are sending out radio waves to communicate with intelligent life, would it ever get to where it was going..I mean if radio waves travel slower than light waves and we shot it out to a distant star...by the time the radio waves got to where they were going...whos to say the star would even exist (now, much less in a million years)?...can someone help me out with this...I mean someone with a PHD in physics or something...if it is true then I have come to the conclusion that the "aliens" would have to be ALOT closer than we give them credit for (say extra dimmensionally)

[ydoaPs]

Radio waves don't travel slower than light waves.......mainly because they ARE light waves.

[dabliss74]

thanks for the clarification that radio waves ARE light waves...can you clarify on anything else in my original post?

[ydoaPs]

A message only takes ~4.5 years to reach the nearest star system. That's not too bad. IIRC, our galaxy is only a few hundred million lightyears across. We'd not be able to receive any reply from that distance, but our descendants will. Our sun is only ~4.5billion years old and it's middle aged. It's highly likely that messages sent to stars in our galaxy(so far as we don't send them to stars that are dying) would be received prior to the death of the system.

[NowThatWeKnow]

... our galaxy is only a few hundred million lightyears across...

 

You mean a few hundred THOUSAND lightyears across. right? Actually, Wikipedia says 100,000 lightyears across, depending on where you define the border.

[ydoaPs]

You mean a few hundred THOUSAND lightyears across. right? Actually, Wikipedia says 100,000 lightyears across, depending on where you define the border.

 

Even better

[NowThatWeKnow]

As mentioned, the Milky way galaxy is about 100,000 light years accross and one of our neighbors, the Andromeda galaxy, is about 2.5 million light years away. You would have to see Earth form 65 million light years away to see the dinosaurs.

 

Depending on their frequency, mass less photons make up radio waves, visible light, infrared light, x-rays, Gama rays etc and travel at the speed of light. Communicating at the speed of light would be painful over long distances. Don't wait up for an answer.

 

Our views of what is possible with science today would leave even advanced technology at a disadvantage for communicating or traveling to distant stars. If the human race does not self destruct, we will probably figure something out some day to make many things possible.

 

I do not have a PHD in physics or anything else so this is the layman's view after hanging around here for awhile and paying attention.

[dabliss74]

ok the amount of light years away for this scenario is irrelevent...I want to know if someone...-as corrected-....65 million light years away were to view us would they be staring at dinosaurs...and if so...WHY in the universe would they try to communicate with them...thats like us finding microbes on mars and trying to communicate with them ...oh BTW if the universe is 13 billion years old....need we not just point hubble in the right direction and see the big bang (if it happened)(along the same line of thought as to reason that half the stars in the sky arent there anymore)

[NowThatWeKnow]

ok the amount of light years away for this scenario is irrelevent...I want to know if someone...-as corrected-....65 million light years away were to view us would they be staring at dinosaurs...and if so...WHY in the universe would they try to communicate with them...thats like us finding microbes on mars and trying to communicate with them ...oh BTW if the universe is 13 billion years old....need we not just point hubble in the right direction and see the big bang (if it happened)(along the same line of thought as to reason that half the stars in the sky arent there anymore)

 

Your eyes see the reflection of light off of an object. You see what happened at the time the light left the object. If you were 65 million years out in space and it was possible to see that far, you may be looking at a T-Rex having dinner.

 

It is not likely that distant civilizations first observe life visually and then try to communicate with them. That would not be practical at the speed of light. Here on earth we just listen for signals from space that may have come from another advanced civilization. What we observe looking out into space happened long long ago and there is no way for us to know what is happening in real time.

 

We can see just after the big bang looking in any direction. The Cosmic Microwave Background Radiation is as close as we can get to seeing the big bang and we currently believe it was not from a singularity.

 

There are some sticky threads at the top of the page that cover some of the basics concerning cosmology and relativity. They may bring you up to speed quicker then asking random questions.

[swansont]

ok the amount of light years away for this scenario is irrelevent...I want to know if someone...-as corrected-....65 million light years away were to view us would they be staring at dinosaurs...and if so...WHY in the universe would they try to communicate with them...thats like us finding microbes on mars and trying to communicate with them ...

 

Because they can't see that they're dinosaurs.