Why 'Accelerated Expansion of the Universe' Contradicts Special Relativity

[metacogitans]

Accelerated expansion, being exponential, would eventually reach relativistic speeds. This would not allow for accelerated expansion for a few reasons:

 

- The exponential increase in relativistic mass would become increasingly substantial, causing the gravitational forces between objects to have a tremendous magnitude, working against accelerated expansion.

 

- As an object approaches the speed of light, the force required to accelerate that object increases. The forces causing accelerated expansion, whatever they might be, would have less and less effect on an object's speed as it approaches the speed of light.

 

- Time dilation would result in no net change in distances being observed, as a slower passage of time would offset measurements made, producing a functional proximity to other objects.

[zapatos]

The expansion of the universe does not involve 'objects approaching the speed of light'.

 

 

 

The metric expansion of space is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes. This is different from other examples of expansions and explosions in that, as far as observations can ascertain, it is a property of the entirety of the universe rather than a phenomenon that can be contained and observed from the outside.

 

 

https://en.wikipedia.org/wiki/Metric_expansion_of_space

[metacogitans]

The expansion of the universe does not involve 'objects approaching the speed of light'.

 

 

 

https://en.wikipedia.org/wiki/Metric_expansion_of_space

Without going into stuff like that wikipedia article not citing any references, or questioning whether space itself expanding is the cause of accelerated expansion,

 

It doesn't matter if the accelerated expansion is caused by space itself expanding or objects being accelerated by a force, because special relativity concerns the travel time of light and the relative velocity of objects. If light's travel time between two objects is increased, the relativistic mass of those objects increases. Pretend the distance between the two objects is "D", and how long it takes light to travel between the objects is used as a metric for time - in one increment of time, light travels D, so the speed of light is 1D/1T . In this case, 'D' can't change, so instead what changes is spacetime at either end of D - which means a gravity well is being produced; hence, an object's relativistic mass increases the faster it is traveling away from an object.

 

But what if we consider more objects? Additional objects will be in the rest-frame of one object more than the other.

 

If the distance between all objects (including individual particles) increased by the same percentage, the net change in position would be 0 - which is why 'space itself expanding' doesn't really hold water as an explanation for accelerated expansion of the universe. If the expansion of space only applies to the space between galaxies and not the space between particles making up those galaxies, then space isn't expanding, it's curving/dilating in the same manner as a gravity well. If that's the case, then expansion can't be accelerating, at least not indefinitely, for reasons described in the first post.

Edited February 26, 2016 by metacogitans

[ajb]

Special relativity is only really about object that 'pass' each other and observers make a comparison of their observations. If space-time is expanding faster than light then this itself is not a problem for special relativity in the sense that no one would measure a relativistic speed greater than the speed of light.

 

The problem is more subtle than that. The basic problem is that the causal structure of such a space-time is not described by the Minkowski metric. The space-time, although possibly flat is not going to be Minkwoski space-time and so we are not dealing with special relativity, other than locally.

[metacogitans]

Special relativity is only really about object that 'pass' each other and observers make a comparison of their observations. If space-time is expanding faster than light then this itself is not a problem for special relativity in the sense that no one would measure a relativistic speed greater than the speed of light.

 

The problem is more subtle than that. The basic problem is that the causal structure of such a space-time is not described by the Minkowski metric. The space-time, although possibly flat is not going to be Minkwoski space-time and so we are not dealing with special relativity, other than locally.

Einstein's Special Relativity is the reworking of classical mechanics to include the implications of the speed of light being a constant -- that is, the same in all directions independent of the motion of its source. It is 'special' because it involves specific inertial reference frames.

'General' Relativity was formed as a result of the broader implications of special relativity, such as gravity. It is 'general' because it describes the geometry of space-time for all inertial frames of reference.

 

I said Accelerated Expansion "contradicts Special Relativity" in my post because it violates implications of the speed of light being a constant, but by that I'm not talking about 'space expanding the size of the universe faster than light' - that's not a problem because the constant isn't always going to be ~ 300,000,000 m/s, because whatever a 'meter' is/was has changed and is still changing. A unit of distance can't be defined without using points of reference; even if we based it off the radius of a hydrogen atom in compounds at specific temperatures, spacetime curvature from gravity will result in more/less radii fitting through a manifold than possible with euclidean geometry, resulting in a meter just being 'whatever' depending on where you are in the universe and how much mass there is.

 

Even if we say the speed of light is given as the distance light travels in one second, what's a second? How was it defined? I believe we defined it based on a specific element's isotope which has an abnormally consistent rate of radioactive decay. How does that hold up though if its heated? Or if we fly it through space at relativistic speeds? Or in the presence of different gravitational wells? It's going to be different.

When its defined as its speed in a vacuum, that's also an erroneous definition, because there is no such thing as a 'true' vacuum, only near-vacuums, and even if there was, light couldn't exist in it because it's a vacuum -- there'd be no source for the light, or anything to measure its speed, and even if there was, how long would the distance be exactly between the source of the light and where we measured it? there's nothing else to use as a point of reference in a vacuum to give us any perspective, so it'd have a value of "indefinite distance" over "some duration of time". Even if the vacuum speed is approximated, we don't realize our approximation was based on measurements of time/distance made in our solar system. Even if we adjust for the mass of everything in our Solar System, nearby stars, our galaxy, and the region of the supercluster we're in, we're still only getting a value that's true for us, and not everyone else.

Edited February 26, 2016 by metacogitans

[swansont]

 

Even if we say the speed of light is given as the distance light travels in one second, what's a second? How was it defined? I believe we defined it based on a specific element's isotope which has an abnormally consistent rate of radioactive decay. How does that hold up though if its heated? Or if we fly it through space at relativistic speeds? Or in the presence of different gravitational wells? It's going to be different.

 

 

It's defined as 9192631770 oscillations of the two (hyperfine split) ground states of an unperturbed Cs-133 atom on the geoid. It's not radioactive decay and it's not "abnormally" consistent. It's just a narrow transition because it has a long lifetime. Doesn't matter if it's heated; you would measure or model that effect and adjust your result accordingly, as with all perturbations.

 

If we fly it through space we would compensate for the time dilation it would experience, exactly like we do with GPS clocks. We also adjust them for their elevation (i.e. position in earth's gravity well)

 

The bottom line is that SR doesn't apply to the situation you are describing, as has already been explained, so it isn't a problem.

 

When its defined as its speed in a vacuum, that's also an erroneous definition, because there is no such thing as a 'true' vacuum, only near-vacuums, and even if there was, light couldn't exist in it because it's a vacuum -- there'd be no source for the light, or anything to measure its speed, and even if there was, how long would the distance be exactly between the source of the light and where we measured it? there's nothing else to use as a point of reference in a vacuum to give us any perspective, so it'd have a value of "indefinite distance" over "some duration of time". Even if the vacuum speed is approximated, we don't realize our approximation was based on measurements of time/distance made in our solar system. Even if we adjust for the mass of everything in our Solar System, nearby stars, our galaxy, and the region of the supercluster we're in, we're still only getting a value that's true for us, and not everyone else.

 

There are several defined units that aren't realized/measured in the conditions under which they are described. But we know how the measurements are affected by the perturbations, so if we can measure what the conditions are, you can compensate for this. e.g. If your length standard was still a physical artifact and was defined at some temperature, you could still measure the length of it at a different temperature and get the right answer if you knew the expansion coefficient and the actual temperature. Or, it might be that you know that the effect was smaller than you could possibly measure and you don't worry about it, because it's a tiny fraction of your measurement uncertainty.

[ajb]

I said Accelerated Expansion "contradicts Special Relativity" in my post because it violates implications of the speed of light being a constant, but by that I'm not talking about 'space expanding the size of the universe faster than light'

I would take this to mean that the global speed of light is not constant, but the local one is. Which is the case in general relativity.

 

As swansont says, the situation you describe is just not special relativity.

[John Cuthber]

What's the issue here?

SR is the "special" case of GR when there are no accelerations.

So it doesn't work in an accelerating system

 

It's like saying that the Bernoulli equation doesn't work for a compressible viscous fluid.

Of course it doesn't; that's not the system it works in.

[ajb]

SR is the "special" case of GR when there are no accelerations.

In this context special relativity is the special case of general relativity for which space-time in Minkowski. Accelerations of bodies in special relativity is okay, as is using non-inertial coordinate systems, but the underlying space-time is still Minkwoski.

[Strange]

Without going into stuff like that wikipedia article not citing any references, or questioning whether space itself expanding is the cause of accelerated expansion,

 

It has 24 references and 7 other external links.

 

It doesn't matter if the accelerated expansion is caused by space itself expanding or objects being accelerated by a force, because special relativity concerns the travel time of light and the relative velocity of objects.

 

Special relativity is irrelevant because you are dealing with something that is (and can only be) described in general relativity.

[metacogitans]

 

There are several defined units that aren't realized/measured in the conditions under which they are described. But we know how the measurements are affected by the perturbations, so if we can measure what the conditions are, you can compensate for this. e.g. If your length standard was still a physical artifact and was defined at some temperature, you could still measure the length of it at a different temperature and get the right answer if you knew the expansion coefficient and the actual temperature. Or, it might be that you know that the effect was smaller than you could possibly measure and you don't worry about it, because it's a tiny fraction of your measurement uncertainty.

In extreme scenarios, how can the perturbations be measured if the apparatus being used is offset as well? For example, say there is a super-massive gas cloud consisting almost entirely out of negative ions, with a mass comparable to stars; and is almost dense enough for fusion to take place. What if due to the extreme negative electric activity and density of the gas cloud, the shape and tiering of electron orbitals was different from what it is on Earth? The physics of how matter behaved would be almost entirely different. Any equipment brought inside the gas cloud, would be destroyed; we could only take measurements from far away and try to assume how things behave differently in the gas cloud than they do elsewhere in the universe.

I know it probably isn't possible for electron orbitals to be different than what they are; or is it? Don't orbitals only take their shape because its the most stable, and wouldn't that be conditional?

[Mordred]

I would suggest looking at electron spectography. In spectography there is unique signatures each element emits (this includes electron orbitals.). When we examine a plasma cloud we can determine the cloud composition via its spectrograph (accounting for redshift)

 

When googling don't worry about the colors, the detail is the frequencies. Spectrographs don't show colors they show frequencies.

( Google typically shows the color spectrum, due to how spectrogaphy was developed)

Here is an extremely basic coverage

 

http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Spectroscopy/Photoelectron_Spectroscopy/Photoelectron_Spectroscopy%3A_Theory

See figure 5

Edited March 1, 2016 by Mordred