Is Space Expanding in a Relativistic Way?

[daisey]

Regarding the expansion of space...

• In one book I've read the diameter of the universe is more than 100B light years across, even though the age of the universe is only roughly 14B years old. This is due to accelerated expansion of space.
• In another book it says that space is expanding in a "relativistic" way, so as the universe expands the length of a meter also gets longer, so the diameter of the universe doesn't change.

These two points seem to be contradictory. Is this issue still up for debate?

 

[phinds]

The length of a meter is not in any way affected by the expansion of the universe. This is not up for debate

(and by the way, the diameter is not > 100B LY, it's something like 94B LY)

 

[daisey]

The length of a meter is not in any way affected by the expansion of the universe. This is not up for debate

Then what is meant by "the scale of space itself changes" in the following sentence?: "The metric expansion of space is the increase of the distance between two distant parts of the universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes" (https://en.wikipedia.org/wiki/Metric_expansion_of_space)

 

[phinds]

Then what is meant by "the scale of space itself changes" in the following sentence?: "The metric expansion of space is the increase of the distance between two distant parts of the universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes" (https://en.wikipedia.org/wiki/Metric_expansion_of_space)

It means that things do not "move apart" in the normal English language sense of that phrase but rather that the geometry of the universe is what is changing such that things in unbound systems get farther apart. That does not mean that a meter changes. A meter is defined as the length of the path traveled by light in a vacuum in 1/299,792,458 of a second.

I recommend the link in my signature.

 

[daisey]

I agree the length of a meter does not change, but only relative to the expansion of space. The universe has always been the same width in "meters". And the length of a meter always remains "the length of the path traveled by light in a vacuum in 1/299,792,458 of a second" because as space expands (and a meter "gets longer") time contracts to allow this distance traveled in a second to remain constant.

Above is the point the author of the second book was trying to make. I understand your argument - I'm thinking there are still disagreements on this point.

 

[PeterDonis]

In one book I've read

What book?

In another book

What book?

I agree the length of a meter does not change, but only relative to the expansion of space. The universe has always been the same width in "meters".

This is not correct. I'm going to guess that neither of the books you referred to was an actual cosmology textbook. I strongly suggest that you consult one.

I'm thinking there are still disagreements on this point.

There aren't, if you mean among actual cosmologists.

 

[daisey]

It's not a textbook, and it is not a book on cosmology. The book is called: "Time Explained", by Michael Savins. Here is the quote from his book.

"The Universe is expanding and that expansion is accelerating but at the same rate as a metre measuring rod is increasing in length. The universe therefore remains the same diameter in metres".

I originally said his point seemed contradictory. But he makes a lot of sense.

 

[PeterDonis]

It's not a textbook, and it is not a book on cosmology.

Then it's not a valid source for PF discussion. Also, it's wrong.

I originally said his point seemed contradictory. But he makes a lot of sense.

Sorry, it's still wrong. You should not be learning science from pop science sources.

Thread closed.