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Cosmic expansion makes no sense

dylancatlow
Posts: 12,253
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8/3/2015 6:16:54 PM
Posted: 1 year ago
To see why this is the case, one must understand the conditions that make "expansion" a meaningful concept. What distinguishes expansion from non-expansion? Expansion amounts to an increase in something's size as a function of time. This just shifts the focus from "expansion" to "size". In order to talk about size (as opposed to mere spatial extension) one must define a background space with a fixed metric. Otherwise, the "size" of the object is simply the size of the object; it cannot be expressed in quantifiable terms.

In order to compare the size of two objects (so as to determine whether expansion has actually occurred), they must both belong to the same spatial metric against which such judgements can be made. Without this, there is no basis for comparison, and thus no way to determine which is larger or smaller. In order to say that something has grown, the growth must be quantifiable within the same spatial metric of the original object. Otherwise, one cannot compare the size of the increase associated with the "expansion" to the original size of the object, in which case one cannot say that an increase in size has actually occurred. So in order for something to expand, it must expand into the same spatial metric in terms of which its original size was quantified.

The implications are obvious: in order to say that the universe is expanding, one must give it a place to expand into. But there's nothing for it to expand into that isn't itself - when it "expands" into external space, it's in a sense "already there", and thus there's no expansion. This means that the size of the universe cannot change in any absolute sense; what we perceive as spatial expansion must be object shrinkage.
johnlubba
Posts: 2,892
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8/3/2015 6:37:56 PM
Posted: 1 year ago
At 8/3/2015 6:16:54 PM, dylancatlow wrote:
To see why this is the case, one must understand the conditions that make "expansion" a meaningful concept. What distinguishes expansion from non-expansion? Expansion amounts to an increase in something's size as a function of time. This just shifts the focus from "expansion" to "size". In order to talk about size (as opposed to mere spatial extension) one must define a background space with a fixed metric. Otherwise, the "size" of the object is simply the size of the object; it cannot be expressed in quantifiable terms.

In order to compare the size of two objects (so as to determine whether expansion has actually occurred), they must both belong to the same spatial metric against which such judgements can be made. Without this, there is no basis for comparison, and thus no way to determine which is larger or smaller. In order to say that something has grown, the growth must be quantifiable within the same spatial metric of the original object. Otherwise, one cannot compare the size of the increase associated with the "expansion" to the original size of the object, in which case one cannot say that an increase in size has actually occurred. So in order for something to expand, it must expand into the same spatial metric in terms of which its original size was quantified.

The implications are obvious: in order to say that the universe is expanding, one must give it a place to expand into. But there's nothing for it to expand into that isn't itself - when it "expands" into external space, it's in a sense "already there", and thus there's no expansion. This means that the size of the universe cannot change in any absolute sense; what we perceive as spatial expansion must be object shrinkage.

What if it is expanding into a space bigger than itself, a bit like a balloon expanding into a space external from the space within the balloon.
dylancatlow
Posts: 12,253
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8/3/2015 6:51:33 PM
Posted: 1 year ago
At 8/3/2015 6:37:56 PM, johnlubba wrote:
At 8/3/2015 6:16:54 PM, dylancatlow wrote:
To see why this is the case, one must understand the conditions that make "expansion" a meaningful concept. What distinguishes expansion from non-expansion? Expansion amounts to an increase in something's size as a function of time. This just shifts the focus from "expansion" to "size". In order to talk about size (as opposed to mere spatial extension) one must define a background space with a fixed metric. Otherwise, the "size" of the object is simply the size of the object; it cannot be expressed in quantifiable terms.

In order to compare the size of two objects (so as to determine whether expansion has actually occurred), they must both belong to the same spatial metric against which such judgements can be made. Without this, there is no basis for comparison, and thus no way to determine which is larger or smaller. In order to say that something has grown, the growth must be quantifiable within the same spatial metric of the original object. Otherwise, one cannot compare the size of the increase associated with the "expansion" to the original size of the object, in which case one cannot say that an increase in size has actually occurred. So in order for something to expand, it must expand into the same spatial metric in terms of which its original size was quantified.

The implications are obvious: in order to say that the universe is expanding, one must give it a place to expand into. But there's nothing for it to expand into that isn't itself - when it "expands" into external space, it's in a sense "already there", and thus there's no expansion. This means that the size of the universe cannot change in any absolute sense; what we perceive as spatial expansion must be object shrinkage.

What if it is expanding into a space bigger than itself, a bit like a balloon expanding into a space external from the space within the balloon.

First, if the universe is contained by some more fundamental space, then that space distributes over the universe in its entirety, in which case it's part of the universe. Second, space is not a "thing" that can be contained like an object can. If it were a thing, then one would be obligated to define a background space to provide its points with a metric of separation, in which case that would be space.
kp98
Posts: 729
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8/3/2015 9:10:10 PM
Posted: 1 year ago
No it doesn't make sense. Neither does special and general relativity or quantum mechanics. Our brains are ok for finding bananas and keeping out of the way of lions (at least most of the time), but they are rubbish at visualising four-dimensional space time and curved space.

The versions of modern science most of us know are - at best- dumbed down metaphors. The universe is a bit like a balloon being inflated - or so I am led to believe - but that's only a suggestive picture, not a definitive statement of the reality. The reality - I fear - can only be expressed by mathematics of the sort I have only vaguely heard of - tensors and such. I'm not too bad at calculus (or I used to not be), which only allows me to see how much better at maths I'd have to be to do physics at even undergrad level !

If the universe was a balloon being inflated then perhaps it doesn't makes any sense, but the universe isn't a balloon being inflated - that is just a 'first approximation', an introductory 'teaching' tool. To get a handle on something nerarer the real truth - and to be in a position to say whether cosmic expansion 'makes no sense' - takes a lot more effort than reading an article in New Scientist or Sci Am.

Perhaps I'm being pessimistic and someone can come up with an intuitive easily understood metaphor for cosmic expansion (or even for the two slit experiment) - but I won't be holding my breath till then.