My understanding was that in a gravitationally bound system like that, the orbits would be slightly larger (or slower for the same distance) based on the rate of expansion and the distance, but not grow any unless the rate of expansion increases. Like maybe the earth is a few angstroms farther from the sun than in a not expanding universe, but that number doesn’t change as long as the expansion keeps going the same. Same for galaxies and clusters.
At the planetary scale, such a change would be completely overpowered by other orbit defining effects, like resonance, mass flow/loss, and even drag.
At the cluster scale, I can absolutely see spacetime expansion overpowering gravity.
At the galaxy level, I can’t tell. Does spacetime expansion limit the size of galaxies? Is that limit shrinking due to the acceleration of expansion? Are galaxies under that limit larger than otherwise expected? Is this effect large enough to effect the speed of galaxy rotation and does it need to be taken into accout when measuring the effects of dark matter?
At the cluster level it will depend on the velocities and distances. For example, using very rough numbers the current expansion rate means that space between us and the Andromeda galaxy is expanding at 55 km/s. Seems fast until you realize the distance needed to see the effect build to this level. For perspective I found someone’s calculation to reduce it to solar system level to end up with ~10 meters/AU/year. But of course at this distance gravity dominates so we can’t measure that directly and it may not even be large enough to consider.
A larger and slower moving galactic cluster would be more affected than a tighter one. I don’t know what our Local Group would be considered to be, but there are a hundred or so galaxies around us that appear blue shifted, so they are moving towards us even with the expansion.
But everything is expanding. Including matter. But the mass isn’t chaning.
But this also includes the space in between the objects.
So objects are getting further apart, but so are the objects getting bigger at the same rate.
The mind bend for me was realsing it’s not space that expanding really, it’s distance.
This is why distant light is red shifted. Because what started out as white, has had the wavelength expand with the universe, making it appear more red.
Yes, all distances are expanding, but not everything in space is expanding. Atoms aren’t expanding because atomic forces are far stronger than expansion is, for example.
Yet the distance between galaxies is increasing, so there must be a crossover point where one structure can stay structured but a slightly bigger structure is torn apart.
My question was if this size is larger or smaller than galaxies, and it seems to be quite a bit larger than galaxies at the moment.
The interesting thing is that the expansion is increasing, so this size limit is shrinking. Unless some change in forses happens (like inflation or some kind of false vacuum collapse) the limit will eventually be smaller than galaxies and they’ll get ripped apart. Eventually star systems will be ripped apart too, then stars (if any remain at that point) then planets, molecules, atoms, and bosons; and if if that continues to quarks funny things start happening that kind of look like the big bang.
That last part is still speculation of course, but I do still wonder if the expansion of the universe affects galaxy formation and dynamics, and if ancient galaxies were different in part because of this.
So yes attoms are expanding. everything is expanding. I mean that very literally.
Let me put it this way.
If you had a million year old meter stick. It would always be a meter. Accurate to the definition of a meter using the wavelength of I don’t remember what off the top of my head. It would always be a meter exactly.
But.
If you magically placed the meter stick next to itself from a million years ago, they would not measure the same. Even though they started with the same definition.
Like I said. Space isn’t expanding. Distance is.
EDIT I don’t mean the distance between things is expanding. The definition of what a distance was is expanding. So yes, attoms, when measured by size (the distance from one edge to another) has also expanded.
But in the same breath, the measured distance never changes. Because the way you use to measure distance has also expanded by the same amount. So nothing ever changes in reality, but everything is just constantly bigger.
What is expanding in this scenario? If atoms are expanding, then either atomic forces have also scaled to match the expansion, or atoms are getting more radioactive?
I don’t understand how atoms are supposed to be expanding in this model. The size of atomic nuclei and electron clouds are governed by the strength and range of the fundamental forces. If everything was expanding in lockstep such that atoms expand but don’t change their properties, then there would be no observable effects. Yet we can see the distance between galaxies not just getting larger, but speeding up.
If orbits, matter, and even the fundamental forces were expanding to match, no such change in “distance” should be possible, beyond the normal movement of matter.
If our metre stick was measured as 1/299,792,458th of a light second, then a million years later it was measured as exactly the same length but was somehow dimensionally larger, then lightseconds must have become larger is lockstep.
If that were true, this expansion could not explain the redshifting of light, as c would increase in lockstep with space, leaving light the same wavelength. Redshifting only happens when the distance between waves increases in relation to the speed of light, and so a universe with redshifting must have a difference in the rate of expansion and the rate of c scaling. Such a difference should be visible as increasing distance or an increase in the flow of time, at minimum.
In your model, everything is expanding equally. Literally everything, including the speed of light, the elementary charge, and even the plank constant, are expanding in lockstep, to the point of unobservability. Is this right?
I am aware of what redshift is. What I don’t understand is how you think a metre bar can expand and the speed of light increase in lockstep with it such than we can’t measure the change.
Let’s say we have a metre bar that’s currently one unit long, and we measure it to be one metre long. There’s also a galaxy a billion light years away.
Let’s say the universe doubles in size after a billion years. The metre bar is two units long, but we still measure it to be one metre long, because the speed of light has doubled (presumably). We measure the light as the same length. The light from the galaxy has now reached us, and is twice as long, but is also moving twice as fast, so the wavelength stays the same. We measure the light as the same length.
Do you see my issue with this situation? How can the measured length of light change (redshift) while the measured length of light also stay the same (metre bar)?
Either redshift isn’t caused by expansion, the fundamental forces and constants are changing as we expand, or space is expanding but matter isn’t. We have good corroborating evidence that redshift is caused primarily by expansion. We also have evidence that the laws of physics haven’t changed significantly in at least the last 2 billion years or across the universe. And lastly, we can measure the acceleration of expansion by several corroborating methods, including redshift.
I’d love to be proven wrong here, the implications of gluons being streched by expansion is fascinating.
I think that expansion doesn’t increase distance, but velocity between objects (or so was my interpretation back when I looked at the formulas). That means that moving objects speed up over time. As such, orbital velocities increase, too, and that lifts their orbit - similar to when a rocket on a closed orbit propulses forward.
But I might be wrong; I feel 70% certain about this one.
But I might be wrong; I feel 70% certain about this one.
You should downgrade your certainty. By a lot.
The expansion is an expansion of space, and therefore explicitly increases the distance between galaxies. It does not, and cannot increase the speed at whoicj those galaxies travel through that space.
Right now, there are galaxies moving away from us at rates higher than the speed of light, a thing which is physically not possible if the expansion is due to an acceleration of the galaxies themselves.
Educate. They said they weren’t sure, so no need to be so critical of their knowledge. You, and all of us reading this, would be better served with a good layman’s explanation rather than you reinforcing how wrong the parent comment was. Twice.
Are you sure that galaxies are growing? They’re gravitationally bound enough to have organized orbits, do those orbits get larger over time?
My understanding was that in a gravitationally bound system like that, the orbits would be slightly larger (or slower for the same distance) based on the rate of expansion and the distance, but not grow any unless the rate of expansion increases. Like maybe the earth is a few angstroms farther from the sun than in a not expanding universe, but that number doesn’t change as long as the expansion keeps going the same. Same for galaxies and clusters.
At the planetary scale, such a change would be completely overpowered by other orbit defining effects, like resonance, mass flow/loss, and even drag.
At the cluster scale, I can absolutely see spacetime expansion overpowering gravity.
At the galaxy level, I can’t tell. Does spacetime expansion limit the size of galaxies? Is that limit shrinking due to the acceleration of expansion? Are galaxies under that limit larger than otherwise expected? Is this effect large enough to effect the speed of galaxy rotation and does it need to be taken into accout when measuring the effects of dark matter?
At the cluster level it will depend on the velocities and distances. For example, using very rough numbers the current expansion rate means that space between us and the Andromeda galaxy is expanding at 55 km/s. Seems fast until you realize the distance needed to see the effect build to this level. For perspective I found someone’s calculation to reduce it to solar system level to end up with ~10 meters/AU/year. But of course at this distance gravity dominates so we can’t measure that directly and it may not even be large enough to consider.
A larger and slower moving galactic cluster would be more affected than a tighter one. I don’t know what our Local Group would be considered to be, but there are a hundred or so galaxies around us that appear blue shifted, so they are moving towards us even with the expansion.
I see where this is diverging a little bit.
But everything is expanding. Including matter. But the mass isn’t chaning.
But this also includes the space in between the objects.
So objects are getting further apart, but so are the objects getting bigger at the same rate.
The mind bend for me was realsing it’s not space that expanding really, it’s distance.
This is why distant light is red shifted. Because what started out as white, has had the wavelength expand with the universe, making it appear more red.
Yes, all distances are expanding, but not everything in space is expanding. Atoms aren’t expanding because atomic forces are far stronger than expansion is, for example.
Yet the distance between galaxies is increasing, so there must be a crossover point where one structure can stay structured but a slightly bigger structure is torn apart.
My question was if this size is larger or smaller than galaxies, and it seems to be quite a bit larger than galaxies at the moment.
The interesting thing is that the expansion is increasing, so this size limit is shrinking. Unless some change in forses happens (like inflation or some kind of false vacuum collapse) the limit will eventually be smaller than galaxies and they’ll get ripped apart. Eventually star systems will be ripped apart too, then stars (if any remain at that point) then planets, molecules, atoms, and bosons; and if if that continues to quarks funny things start happening that kind of look like the big bang.
That last part is still speculation of course, but I do still wonder if the expansion of the universe affects galaxy formation and dynamics, and if ancient galaxies were different in part because of this.
So yes attoms are expanding. everything is expanding. I mean that very literally.
Let me put it this way.
If you had a million year old meter stick. It would always be a meter. Accurate to the definition of a meter using the wavelength of I don’t remember what off the top of my head. It would always be a meter exactly.
But.
If you magically placed the meter stick next to itself from a million years ago, they would not measure the same. Even though they started with the same definition.
Like I said. Space isn’t expanding. Distance is.
EDIT I don’t mean the distance between things is expanding. The definition of what a distance was is expanding. So yes, attoms, when measured by size (the distance from one edge to another) has also expanded.
But in the same breath, the measured distance never changes. Because the way you use to measure distance has also expanded by the same amount. So nothing ever changes in reality, but everything is just constantly bigger.
Physics is full of hard to explain paradoxes.
What is expanding in this scenario? If atoms are expanding, then either atomic forces have also scaled to match the expansion, or atoms are getting more radioactive?
I don’t understand how atoms are supposed to be expanding in this model. The size of atomic nuclei and electron clouds are governed by the strength and range of the fundamental forces. If everything was expanding in lockstep such that atoms expand but don’t change their properties, then there would be no observable effects. Yet we can see the distance between galaxies not just getting larger, but speeding up.
If orbits, matter, and even the fundamental forces were expanding to match, no such change in “distance” should be possible, beyond the normal movement of matter.
If our metre stick was measured as 1/299,792,458th of a light second, then a million years later it was measured as exactly the same length but was somehow dimensionally larger, then lightseconds must have become larger is lockstep.
If that were true, this expansion could not explain the redshifting of light, as c would increase in lockstep with space, leaving light the same wavelength. Redshifting only happens when the distance between waves increases in relation to the speed of light, and so a universe with redshifting must have a difference in the rate of expansion and the rate of c scaling. Such a difference should be visible as increasing distance or an increase in the flow of time, at minimum.
In your model, everything is expanding equally. Literally everything, including the speed of light, the elementary charge, and even the plank constant, are expanding in lockstep, to the point of unobservability. Is this right?
Yes everything is expanding like that.
Look back to the red shifted light.
When a white star starts with white light, has the literal wavelength expanded to be more red looking.
https://www.esa.int/Science_Exploration/Space_Science/What_is_red_shift
It’s the literal light getting shifted. So the speed of light is the same, but the distance it travels in a given time is not. Making it red shifted.
I am aware of what redshift is. What I don’t understand is how you think a metre bar can expand and the speed of light increase in lockstep with it such than we can’t measure the change.
Let’s say we have a metre bar that’s currently one unit long, and we measure it to be one metre long. There’s also a galaxy a billion light years away.
Let’s say the universe doubles in size after a billion years. The metre bar is two units long, but we still measure it to be one metre long, because the speed of light has doubled (presumably). We measure the light as the same length. The light from the galaxy has now reached us, and is twice as long, but is also moving twice as fast, so the wavelength stays the same. We measure the light as the same length.
Do you see my issue with this situation? How can the measured length of light change (redshift) while the measured length of light also stay the same (metre bar)?
Either redshift isn’t caused by expansion, the fundamental forces and constants are changing as we expand, or space is expanding but matter isn’t. We have good corroborating evidence that redshift is caused primarily by expansion. We also have evidence that the laws of physics haven’t changed significantly in at least the last 2 billion years or across the universe. And lastly, we can measure the acceleration of expansion by several corroborating methods, including redshift.
I’d love to be proven wrong here, the implications of gluons being streched by expansion is fascinating.
Yes, I think they do.
I think that expansion doesn’t increase distance, but velocity between objects (or so was my interpretation back when I looked at the formulas). That means that moving objects speed up over time. As such, orbital velocities increase, too, and that lifts their orbit - similar to when a rocket on a closed orbit propulses forward.
But I might be wrong; I feel 70% certain about this one.
You should downgrade your certainty. By a lot.
The expansion is an expansion of space, and therefore explicitly increases the distance between galaxies. It does not, and cannot increase the speed at whoicj those galaxies travel through that space.
Right now, there are galaxies moving away from us at rates higher than the speed of light, a thing which is physically not possible if the expansion is due to an acceleration of the galaxies themselves.
You’ve misunderstood things completely backwards.
Educate. They said they weren’t sure, so no need to be so critical of their knowledge. You, and all of us reading this, would be better served with a good layman’s explanation rather than you reinforcing how wrong the parent comment was. Twice.