Thread: Eternal vs. Infinite: Are these words used differently in Cosmology?

I take eternal and infinite to by synonyms to mean that something has always existed.

I was just curious if in cosmology the words are used slightly different. For example, some say our universe is bound/predicted to expand infinitely but then deny that our universe is eternal and that it definitely had a "beginning" at the BB.

In a documentary I saw on TV (I can't recall the exact title), the same physicist said in one part of the show that the universe indeed did have a beginning but then, at a later part, said that we may be one of the many BB that has happened and it could be the case that we've banged before. If so, if we've banged before, does this not count as eternal? Maybe I'm the one who is confused here.

How is it that some cosmologists/physicists say that our universe did indeed begin (not eternal) but yet in another sentence support the idea of multiple BB prior to the BB that resulted in us and support the idea of multiverse?

Help me out.

Originally Posted by Tau Ceti

I take eternal and infinite to by synonyms to mean that something has always existed.

Infinite doesn't mean that.
Eternal relates to time, infinite relates to spacial extent.

How is it that some cosmologists/physicists say that our universe did indeed begin (not eternal) but yet in another sentence support the idea of multiple BB prior to the BB that resulted in us and the idea of multiverse?

Because they're distinguishing between our universe (the one we currently inhabit) and any other (possible) universe[s] - that we have zero knowledge and experience of.

Originally Posted by Tau Ceti

For example, some say our universe is bound/predicted to expand infinitely but then deny that our universe is eternal and that it definitely had a "beginning" at the BB.

There are an infinite amount of positive integers - but they start at 1.

What is a good read on the topic of cosmology that is written in an easy to understand manner?

I take eternal and infinite to by synonyms to mean that something has always existed.

No, that would a logical fallacy. Something being eternal/infinite does not mean that it didn't have a beginning. For example, the universe can have originated in a Big Bang event, and then just keep expanding forever. That would make it eternal, but it still has a beginning.

Originally Posted by Tau Ceti

I take eternal and infinite to by synonyms to mean that something has always existed.

I was just curious if in cosmology the words are used slightly different. For example, some say our universe is bound/predicted to expand infinitely but then deny that our universe is eternal and that it definitely had a "beginning" at the BB.

In a documentary I saw on TV (I can't recall the exact title), the same physicist said in one part of the show that the universe indeed did have a beginning but then, at a later part, said that we may be one of the many BB that has happened and it could be the case that we've banged before. If so, if we've banged before, does this not count as eternal? Maybe I'm the one who is confused here.

How is it that some cosmologists/physicists say that our universe did indeed begin (not eternal) but yet in another sentence support the idea of multiple BB prior to the BB that resulted in us and support the idea of multiverse?

Help me out.

Science stands and falls by definition. It is VERY VERY important to name things as they are. But immediately noting this,... you have a problem. Their are thousands of languages all over the world. The northern Inuit -I was told- have many ways to describe snow and ice (I recall they have about 20 words,.. but I can not back this up by factual knowledge), while in the not so cold area's we have far few.

My mathemathician teacher in school once told my class:
'The greatest invention of mankind ever,... was the definition of ZERO.'

Definitions are important in science. Be always sure that which you tell or try to teach,... is well understood in other languages.

Originally Posted by Estheria Quintessimo

Definitions are important in science. Be always sure that which you tell or try to teach,... is well understood in other languages.

True enough - and that is one of the reasons why the language physical ideas are expressed in is mathematics, rather than actual spoken languages. Maths is rigorous, unambiguous, and concise, and all meanings are well defined.

And yet there is no excuse - at least for native speakers - to screw up well established meaning, or grammatical rules.

1. So, let us repeat the Duck's admonition. Eternal relates to time annd infinite to space. It is simple. There is no excuse for confusing the two.
2. There are not any amount of integers. Amount refers to a continuous quantity. Integers, by definition, are discrete. Therefore there are any number of integers.

This ends this brief interjection by the Society of Grumpy Old Pedantic Men.

Originally Posted by John Galt

And yet there is no excuse - at least for native speakers - to screw up well established meaning, or grammatical rules.

Also true.

Eternal relates to time annd infinite to space. It is simple. There is no excuse for confusing the two.

Except that there is neither space nor time, but only space-time in the real world. Thus, the word "eternal" shouldn't be used at all - the correct term is always "infinite" in this context.

Originally Posted by Estheria Quintessimo

The northern Inuit -I was told- have many ways to describe snow and ice (I recall they have about 20 words,.. but I can not back this up by factual knowledge), while in the not so cold area's we have far few.

While we are being picky, this is a myth.
Language Log » "Words for snow" watch