expanding universe conundrum

[emil]

The expanding universe theory illustrates that objects viewed in space are moving away from one another and the further we look into space, the faster this movement is detected. My problem with that theory is that the further we look into space, the further we go back in time, due to light having a finite velocity, so we are using non-current observational data going back as far as billions of (light) years to come up with a theory of a currently expanding universe.If we have no way of knowing what velocity distant objects are CURRENTLY travelling at, but are only measuring the redshift of their image emitted aeons ago, then this theory doesnt make sense to me. In fact it seems that all it illustrates is that the further in time you look back , the faster the universe WAS expanding, and the closer to the current time you view objects, the slower the expansion is occurring, so it must mean the expansion is slowing.

[mathematic]

Studies about 20 years ago showed the expansion is speeding up.

[Strange]

The thing is, what we see is the relationship between the distance the objects were at the time we see them and the (apparent) velocity then. So the most distant galaxies we see, which appear to be about 13 billion light years away are now actually about 46 billion light years away (and receding even faster). But when the light we see left them, they were only about 4.5 billion light years away.

 

Also, the apparent recession of galaxies is not really caused by their movement, but by the scaling of the distances between them (a subtle but important distinction). This means that the relationship between distance and velocity is purely a matter of geometry - you can demonstrate this for yourself with some simple diagrams - and nothing to with cosmology.

 

If all of that sounds confusing, it is because this not a simple concept and the only way to really get your head round it is to understand the math (which, I happily admit, I do not fully!)

 

However, you are right in that it is entirely possible that stars a billion light years away could have reversed direction, exploded, danced a jig or turned to chocolate and we wouldn't know for a billion years. But what we do have are models based on what we can see. These models make all sorts of predictions (e.g. the nature cosmic microwave background, the primordial proportions of elements, etc) which can all be tested. And, so far, the predictions of the model stand up pretty well. So, until there is evidence to contrary, it is thought that the most distant galaxies are receding at ever greater speeds.

[emil]

In reply to your answer, my first thought is that the 46 billion light years distance you state as fact, is based on the very assumption I am questioning, it is not a fact, but a theory.The problem here is that we do not have direct, current and applicable evidence of objects receding at stated speeds in the expansion universe theory, only past/dated evidence.How can one explain away the question of using inappropriate data in the formulation of the expansion theory, whether by a physicist or a computer model? Can this still be termed as Science using precise measurement, or is this the process of square shaped data being hammered through a round hole till it fits? I`m certainly no scientist , but it seems to me that a models` scientific value is only as good as the scientific value of the data put into it, therefore, a theory postulating current expansion of the universe based on non-current data immediately falls over. I`m not the best at illustrating my point with examples, but wouldn`t it be something like using earth surface data taken millions of years ago to produce a map of the current world? If somebody has argued the point I`m making here before, I would be very grateful to the person who could point me in the direction of that material. I have only just discovered this website and I would like to thank anyone who takes the time to discuss this with me.

[Strange]

In reply to your answer, my first thought is that the 46 billion light years distance you state as fact, is based on the very assumption I am questioning, it is not a fact, but a theory.The problem here is that we do not have direct, current and applicable evidence of objects receding at stated speeds in the expansion universe theory, only past/dated evidence.

 

True. But that is true to some extent for all science. Cosmology is, perhaps, a more extreme example.

 

 

How can one explain away the question of using inappropriate data in the formulation of the expansion theory, whether by a physicist or a computer model?

 

Well, its no inappropriate data; the observations we make are the only data we have. All models/theories that attempt to explain the universe need to be based on that same data. There have been (and are) other models that attempted to explain the evidence. Currently, none of them fit ALL the evidence as well as the big bang model.

 

As ar as the model is concerned, this is general relativity which is extremely well tested in every way we can think of. Many of these are far more direct that these observations, which you are doubtful about. So any explanation needs to be consistent with GR. Having a universe that doesn't expand (or contract) is a big problem in that respect.

 

 

If somebody has argued the point I`m making here before, I would be very grateful to the person who could point me in the direction of that material.

 

It has come up on this (and other) forums before. And other people have given far better answers than me!

 

If you want to get really good answers, possible from people actually working in the field, I would recommend the Cosmoquest forum. (There are some experts here, but not as many or as regularly.)