# Looking back in time

## Main Question or Discussion Point

I had a physics lesson at school lately and i stated that by looking at the stars we are looking back in time because the light takes a long time to reach our planet therefor we are looking back when the star's light first is sent off/ received by us. The teacher then said that this was not true as it is virtually impossible to look back in time. I did not believe him. Please tell me the truth.

Thankyou,
Entropy+time=fun

P.S. I am new here and am not sure whether this is the right place to post this query and also i would like to make some friends.

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If thats the only reply he made he doesn't seem like much of a teacher...you should have asked him to expand on his opinion. What you stated seems accurate so I don't understand why he would just say it's not true and leave it at that.

It's true that time flows in only one direction (forward) and we can't observe it to go backwards, so in that sense we can't see the past. We still observe events that happened in the past, and we are affected by them.

pervect
Staff Emeritus
In comoving cosmological coordinates, it turns out that looking out in a straight line *does* involve moving backwards in cosmological time (the time coordinate of the cosmological coordiante system).

"Comoving coordinates" means that one assigns fixed spatial coordinates to the stationary galaxies, the galaxies 'at rest' compared to the cosmic microwave background. One assigns a time coordinate to the galaxies based on the elapsed time since the big bang.

In this coordiante system, a straight line in space actually moves backwards in cosmological time!

It is rather hard to explain why this happens without using calculus and the geodesic equation.

Mk
entropy+time=fun said:
I had a physics lesson at school lately and i stated that by looking at the stars we are looking back in time because the light takes a long time to reach our planet therefor we are looking back when the star's light first is sent off/ received by us. The teacher then said that this was not true as it is virtually impossible to look back in time. I did not believe him. Please tell me the truth.

Thankyou,
Entropy+time=fun

P.S. I am new here and am not sure whether this is the right place to post this query and also i would like to make some friends.
Well, it would be tough to watch yourself play a game of poker the night after you lost. Events are what he asumed whoever said it was talking about. The light from the stars you see was released x years ago, so the stars you are seeing look how they were, the x number years ago. Thats what they mean by "looking back in time."

Ohh, ohh, I'll be your friend :!!) . It only costs five bucks!

Danger
Gold Member
Mk said:
Ohh, ohh, I'll be your friend :!!) . It only costs five bucks!
And a rip-off at half the price. :tongue:

Entropy, it sounds to me as if your teacher is one of those whose only formal education is in teaching, and has been assigned to teach physics. Tell him (politely) that he's a freaking moron and hand him a print-out of pervect's response. If he has a problem with it, send him to us.

Thanks a lot guys i knew that jerk was wrong.

Danger
Gold Member
I've had enough beer now to go into proper 'Danger' mode. Just for the hell of it, give him a UV lamp and tell him that by studying black light you can see ahead in time.

coolio that jerk wont know what hit him. hahahahahah..... the power of time!!

By the way Danger how does that idea work, you know with black light, please explain. I am only a lowly 13 year old and dont have too much knowledge stored away. Thanks.

P.S I know its not the right place , but how do you get an avatar up????

Danger
Gold Member
entropy+time=fun said:
By the way Danger how does that idea work, you know with black light, please explain.
It doesn't; I just like to screw with people's heads (people like your teacher, I mean—not you). It was a joke. If, on the other hand, you mean how black light works in general, it's just a matter of it not being within the visible spectrum. It does react with certain other materials to cause fluorescence. Some things like poster paints absorb UV and then re-emit the light at visible frequencies.

entropy+time=fun said:
how do you get an avatar up????
You have to become a 'contributer'; ie. send in \$25 to help Greg keep this puppy on its feet. It's certainly a most worth-while investment.

ok, thanks a lot Danger!