Big Bang+Distance of a New Star

[Gonçalo]

Question

When astronomers find a new star, say 15 billion light years away, why do they immediately relate that distance with the age of the Universe (the distance to the Big Bang point)?



--->cause if the Universe were like a balloon, and the Earth and the star were in the the surface of that ballon, their distance could be much bigger than the distance of the Earth to the Big Bang point!...

 

[meteor]

Hi, neighbour
It's not possible to localize stars at 15 billion year lights of distance. In fact, is very difficult to localize galaxies at that distance, imagine stars!
Actually is believed that the big bang didn't started in a point, but that started in an infinite extension of spacetime

 

[Ambitwistor]

Originally posted by Gonçalo
When astronomers find a new star, say 15 billion light years away, why do they immediately relate that distance with the age of the Universe (the distance to the Big Bang point)?

They don't. They usually leave it in terms of redshift. They only try to translate it into a distance when speaking to the media or laymen. (There are different ways of doing that, depending on what you mean by "distance".)

Also, there was no "Big Bang point" or distance to it: the Big Bang occurred everywhere in space.

--->cause if the Universe were like a balloon, and the Earth and the star were in the the surface of that ballon, their distance could be much bigger than the distance of the Earth to the Big Bang point!...

In the balloon analogy, the surface of the balloon is all of space. There is no space "inside" the balloon, and it doesn't make sense to speak of the distance to anything inside the balloon.

 

[Phobos]

Welcome to Physics Forums!

Both good responses. One more thing to help clarify...

Due to the finite speed of light, the farther away something is, the older the image is (seeing images from the past). So, if you look at a star that is 1000 light years away (about 6 quadrillion miles away), you are seeing an image that is 1000 years old (i.e., how that star looked 1000 years ago).

So, the further the object you see, the further back you see in time...closer and closer to the Big Bang which occurred about 13.7 billion years ago. And as explained above, the Big Bang happened, not at a point in space, but at EVERY point in space.