Cosmic inflation: is it how the universe began? is a great introduction to inflation theory (the time before the hot Big Bang). The first chapter of my book, Impacts, was reviewed by Andrei Linde,...
Cosmic inflation: is it how the universe began? is a great introduction to inflation theory (the time before the hot Big Bang). The first chapter of my book, Impacts, was reviewed by Andrei Linde, who was one of the main authors of the inflationary universe theory.
A good analogy from PBS spacetime that stuck with me is to imagine that things aren't really moving; space is being created between things. So 100 kms to a star becomes 200 KMs, a million, a...
A good analogy from PBS spacetime that stuck with me is to imagine that things aren't really moving; space is being created between things. So 100 kms to a star becomes 200 KMs, a million, a billion, etc. It looks to us as if we're racing away from each other, but it's just the expansion of space.
This is how an infinite universe can even expand, and you can model it very easily on a piece of paper. 20 kms between two objects, 10 kms, 1 cm, 0. You've just now collapsed an infinite universe into a single point, and it didn't take any calculus to do it. Doesn't matter how big the universe is, if the distance between all objects is zero, they're all in the same point now.
The problem is with what happened in the (very, very, very) early moments after the big bang: the expansion happened faster than the speed of light, something that would be impossible when you...
The problem is with what happened in the (very, very, very) early moments after the big bang: the expansion happened faster than the speed of light, something that would be impossible when you assume movement. But there is no such limit (that we know of) with adding space-time between everything.
Honestly (and I know I'm making a fool out of myself debating astrophysics) it's something that always bothered me about the explanation. Note that my source is pop culture physicists talking in...
Honestly (and I know I'm making a fool out of myself debating astrophysics) it's something that always bothered me about the explanation. Note that my source is pop culture physicists talking in front of green screens in BBC documentaries.
Nothing can be faster than the speed of light, tough luck. But then there's just a re-definition of "fast" (time it takes to move from point A to B) and it's ok again. Wouldn't it be more likely that the speed of light limit is just a fundamental misunderstanding of "fast" and "timespace expanding" is just a way of bending our wrong math to make it show the right numbers? Couldn't you unwind this mess into just mass traveling at different speeds in different parts of space? I guess I'm just confused as to why we need two types of physics to explain movement, it seems like one was just inaccurate.
I'm a layman myself but the expansion of the universe does not describe movement AFAIK. It describes literally more space being created. I think it's us trying to apply very basic ideas of speed...
I'm a layman myself but the expansion of the universe does not describe movement AFAIK. It describes literally more space being created.
I think it's us trying to apply very basic ideas of speed and movement to conversations that call for different definitions.
@itdepends already beat me to the point, but I'll expand on their point a little. One of the main causes of confusion/misunderstanding about both relativity and quantum dynamics (don't worry,...
@itdepends already beat me to the point, but I'll expand on their point a little.
One of the main causes of confusion/misunderstanding about both relativity and quantum dynamics (don't worry, those won't play a part in this) are subtle differences and fuzziness in definitions in the everyday usage of words and their usage in scientific fields (same goes for engineering, law, economics, etc.).
Here the difference is what we mean by speed, with "fast" essentially only meaning a high value of speed. It's defined by the change of the location of something over some specified time. This change in location is usually described by some distance. But importantly, you have to remember that it's the location that is changing. The distance-value being used is just how we quantify the change (i.e. give it an actual value).
So, how does this factor in the discussion about the faster-than-light expansion of the early univers? Well, simply said, all the particles and what not that existed back then didn't actually move, as in their location didn't change, but still the distances between everything increased.
A typical analogy for this is to draw two marks on a partially inflated balloon and to then inflate it even more. The marks don't move as such (because they can't, they are bits of ink on rubber), there is now simply more "balloon space" between them.
It's the reason why relativity is so damn counterintuitive and difficult to grasp: it's fundamental assumptions about space and time go directly against everything we experience day to day in our lives. But despite that, it provides us with the most accurate predictions about the universe (on a large scale, for small stuff you need quantum mechanics) that we've ever had.
I appreciate these analogies but I can’t help but think of the dots on the inflated balloon physically moving away from each other from an outside point of view, even if still part of the same...
I appreciate these analogies but I can’t help but think of the dots on the inflated balloon physically moving away from each other from an outside point of view, even if still part of the same balloon. I assume the problem lies with there not being a perfect birthday-party-equipment analogy for weird mathematical formulas explaining astrophysics. But it’s still confusing to me how the basic concept seems so hard to explain. There are not that many moving parts (literally) in it.
Here I am chiming in again with my zero qualifications (sorry) but what immediately strikes me is that when discussing the universe we do not have an outside perspective. It's the biggest of big...
Here I am chiming in again with my zero qualifications (sorry) but what immediately strikes me is that when discussing the universe we do not have an outside perspective. It's the biggest of big scope pictures we can have.
And again keep in mind that we're receiving these information from scientists in the easiest to digest form so they have to say "further" and "faster" and "it's like a seal vacationing in Nepal" instead of linking us to a 400page paper that would require 10years of studying to understand.
At least that's just how i reconcile those mind-boggling revelations with my idiot's understanding.
The concept is difficult to explain because it is completely unlike anything we experience in day-to-day life. This tends to be case for all extremes of physics, like traveling at a significant...
The concept is difficult to explain because it is completely unlike anything we experience in day-to-day life. This tends to be case for all extremes of physics, like traveling at a significant percentage of the speed of light or dealing with the behavior of subatomic particles. Things like the fact that light can't go any faster even if you're moving toward the light source or pretty much everything we learn from the double slit experiment are pretty counterintuitive imo.
I think we can say that the unreconcilable difference is acceleration. As a hypothetical, consider two objects a distance of 100 meters away from each other at time t=0, and 200 meters distance...
I think we can say that the unreconcilable difference is acceleration.
As a hypothetical, consider two objects a distance of 100 meters away from each other at time t=0, and 200 meters distance from each other at time t=1, where neither object is experiencing any acceleration and the perceived movement is straight away from each other.
If there is no spatial expansion, then they are moving away from each other at 100 meters per time unit.
If the change in distance is entirely up to space expanding, then space is doubling every time unit.
If we then look at time t=2, these two models will give different predictions.
In the velocity model, the velocity remains constant and we expect to see the objects 300 meters apart, and measure a speed of 100 meters per time unit.
In the spatial expansion model, we expect space to continue expanding in proportion to itself, so double the distance again so that the objects are 400 meters apart, and the distance between them to be increasing by more than 100 meters per time unit.
In essence, it's the difference between a linear and exponential distance prediction when under no acceleration.
This reminds me of an interesting paper I came across a few years ago, that instead of having the Universe expand, with its spacetime increasing (being a bit vague here, to prevent it getting too...
This reminds me of an interesting paper I came across a few years ago, that instead of having the Universe expand, with its spacetime increasing (being a bit vague here, to prevent it getting too math heavy), but instead turning it around:
Instead, have all particles shrink. This would be done with having all the constants change with time.
You would effectively still get the same results. It would still appear to us as if the Universe is expanding due to everything shrinking. Really, there isn't any good reason to prefer one model or the over except that expansion is a bit easier to understand for our brains. Which, frankly, the Universe doesn't care about. It's not very different from picking a different reference frame.
I'm still not sure whether I find it brilliant, trivial, or both.
So in one hypothesis you leave everything as is except one value (amount of space-time), while in the other hypothesis you leave that value alone and instead have literally every fundamental...
So in one hypothesis you leave everything as is except one value (amount of space-time), while in the other hypothesis you leave that value alone and instead have literally every fundamental constant be variables instead.
I know which hypothesis I find more convincing and I think Mr. Occam would agree with me.
Except that they would be tied together, it's not as much as that you change every single variable in a perfect fit. It does not require all particle masses to be changed perfectly, as the ratios...
Except that they would be tied together, it's not as much as that you change every single variable in a perfect fit. It does not require all particle masses to be changed perfectly, as the ratios remain constant. Occam's razor doesn't really prefer one or the other if you ask me.
It's not about them being tied together or not, it's about them not being constant. Before Einsteins theories of relativity, we assumed both space, time and all other fundamental constants of the...
It's not about them being tied together or not, it's about them not being constant.
Before Einsteins theories of relativity, we assumed both space, time and all other fundamental constants of the universe to be, well, constant.
With the "typical" model of inflation by increasing the "amount" of space-time, we only change 3 of our assumptions: space and time are not constant and are actually intrinsically linked like electromagnetism.
For the "shrinking" model to work, the 19 known fundamental constants (according to Wikipedia) would all have to be indeed be changeable and would had to have changed in precisely such a way that the universe as we know it would even be possible.
It's simply that the number and severity of the different assumptions is vastly different while both explanations are coming to the same result, which is precisely one of the prime examples of where Occam's razor should be used.
So I have to confess: my earlier comments was kinda oversimplified, and I was trying to expand on to that. Then, I began to expand that in this comment, and now I'm conceding to your point, but...
So I have to confess: my earlier comments was kinda oversimplified, and I was trying to expand on to that. Then, I began to expand that in this comment, and now I'm conceding to your point, but not in the way I expected? This is going to be an unusual format for an Internet comment, but let me first the comment that I wanted to put in:
"These are good points, and I think(emphasis here, I could be wrong here about what you're trying to communicate) that in a part its my fault and not necessarily the concept. Because despite what I said earlier, you can actually have the exact same amount of constants, but with different variables."
But then I realised a few things that don't hold up. First, your metrics would need to accommodate too. Making cosmological red-shift a bit of a mess. While it may technically not be adding extra assumptions to your model to get consistent results, it's a bit like putting extra coordinate transformations in Maxwell's equations and seeing it's equally valid. It kinda is, but it doesn't make sense to treat it as equal per se. And while I can't rule out future discoveries for a shrinking model, it's a bit weird to do it now, apart from as an interesting thought experiment.
The second one is a bit more damning. Inflation and dark energy. These two are already messy of its own, but then putting them in the context of this model gets weird. In the case of inflation you would have to add extra energy to changing the constants. Whereas with the position-time <-> energy-momentum switch you can, in a pure mathematical sense, get around it, I don't think you can do that with inflation? It's been years since I took my course in cosmology so I'm looking over some papers of it, but unless you make the potential of the inflation time dependent it just won't work?
And inflation already being (more or less) born out of Occam's razor, it would be weird to adjust it like that... as a counterargument against Occam's razor. This contradicts my earlier statement pretty thoroughly. And even if there is a mathematical workaround... I don't think that could survive dark energy at the same time.
There is probably more but I think it's one of those things you can't really dig your way out to unless something big changes in Cosmology. Not impossible, but unlikely. Anyway, you're right, it can't really survive Occam's razor. At least, not in a way I can't argue against it.
As a matter of fact I did not know of the two ways that you can describe systems, so thank you very much for mentioning and linking to it! Also, considering you actually have taken courses in...
As a matter of fact I did not know of the two ways that you can describe systems, so thank you very much for mentioning and linking to it!
Also, considering you actually have taken courses in cosmology, you most definitely know way more on the topic (and more in depth as well) than I do. I'm just a layman with ADHD and too much time on his hands from time to time, which leads me to know a little bit about a lot of things.
So I freely admit that I wasn't entirely able to follow the depths of the latter half of your comment, but that's entirely on me for not having the prerequisite knowledge and understanding of the topics being discussed.
What I do entirely agree with is that the shrinkage scenario could become much more likely should some new discoveries change our understanding of cosmology. But for now, it unfortunately falls under Occam's razor.
Thanks again for your very interesting and informative comment!
It is hardly Mr. Occam's fault that we picked length, the one fleeting thing in our universe [according to RC's hypothesis], as the unit we base almost all of our other units on. It's literally...
It is hardly Mr. Occam's fault that we picked length, the one fleeting thing in our universe [according to RC's hypothesis], as the unit we base almost all of our other units on. It's literally the metric system. As in meter. We picked a unit of length and made everything depend on that.
You could perfectly well define lengths via the hubble constant. It would be a brain-melting system of units to work with, but not because it is inherently more complex, just more convoluted for human intuition. If my intuition is right, defining lengths via hubble's constant (or an adjecent concept perhaps) would give you the system of units where the constants are constants again. Perhaps they're all constant factors of this one other constant that changes with time.
Cosmic inflation: is it how the universe began? is a great introduction to inflation theory (the time before the hot Big Bang). The first chapter of my book, Impacts, was reviewed by Andrei Linde, who was one of the main authors of the inflationary universe theory.
I prefer the Star Size Comparison 3 video to the one presented by David Mulryne.
Your book is really cool! In print form it would make a great coffee table book, IMO. The art and subject matter reminds me of Kurzgesagt. :)
A good analogy from PBS spacetime that stuck with me is to imagine that things aren't really moving; space is being created between things. So 100 kms to a star becomes 200 KMs, a million, a billion, etc. It looks to us as if we're racing away from each other, but it's just the expansion of space.
This is how an infinite universe can even expand, and you can model it very easily on a piece of paper. 20 kms between two objects, 10 kms, 1 cm, 0. You've just now collapsed an infinite universe into a single point, and it didn't take any calculus to do it. Doesn't matter how big the universe is, if the distance between all objects is zero, they're all in the same point now.
I don’t get it. You can just add up the distances and it’s the same situation as if they were moving, just with reversed math.
The problem is with what happened in the (very, very, very) early moments after the big bang: the expansion happened faster than the speed of light, something that would be impossible when you assume movement. But there is no such limit (that we know of) with adding space-time between everything.
Honestly (and I know I'm making a fool out of myself debating astrophysics) it's something that always bothered me about the explanation. Note that my source is pop culture physicists talking in front of green screens in BBC documentaries.
Nothing can be faster than the speed of light, tough luck. But then there's just a re-definition of "fast" (time it takes to move from point A to B) and it's ok again. Wouldn't it be more likely that the speed of light limit is just a fundamental misunderstanding of "fast" and "timespace expanding" is just a way of bending our wrong math to make it show the right numbers? Couldn't you unwind this mess into just mass traveling at different speeds in different parts of space? I guess I'm just confused as to why we need two types of physics to explain movement, it seems like one was just inaccurate.
I'm a layman myself but the expansion of the universe does not describe movement AFAIK. It describes literally more space being created.
I think it's us trying to apply very basic ideas of speed and movement to conversations that call for different definitions.
@itdepends already beat me to the point, but I'll expand on their point a little.
One of the main causes of confusion/misunderstanding about both relativity and quantum dynamics (don't worry, those won't play a part in this) are subtle differences and fuzziness in definitions in the everyday usage of words and their usage in scientific fields (same goes for engineering, law, economics, etc.).
Here the difference is what we mean by speed, with "fast" essentially only meaning a high value of speed. It's defined by the change of the location of something over some specified time. This change in location is usually described by some distance. But importantly, you have to remember that it's the location that is changing. The distance-value being used is just how we quantify the change (i.e. give it an actual value).
So, how does this factor in the discussion about the faster-than-light expansion of the early univers? Well, simply said, all the particles and what not that existed back then didn't actually move, as in their location didn't change, but still the distances between everything increased.
A typical analogy for this is to draw two marks on a partially inflated balloon and to then inflate it even more. The marks don't move as such (because they can't, they are bits of ink on rubber), there is now simply more "balloon space" between them.
It's the reason why relativity is so damn counterintuitive and difficult to grasp: it's fundamental assumptions about space and time go directly against everything we experience day to day in our lives. But despite that, it provides us with the most accurate predictions about the universe (on a large scale, for small stuff you need quantum mechanics) that we've ever had.
I appreciate these analogies but I can’t help but think of the dots on the inflated balloon physically moving away from each other from an outside point of view, even if still part of the same balloon. I assume the problem lies with there not being a perfect birthday-party-equipment analogy for weird mathematical formulas explaining astrophysics. But it’s still confusing to me how the basic concept seems so hard to explain. There are not that many moving parts (literally) in it.
Here I am chiming in again with my zero qualifications (sorry) but what immediately strikes me is that when discussing the universe we do not have an outside perspective. It's the biggest of big scope pictures we can have.
And again keep in mind that we're receiving these information from scientists in the easiest to digest form so they have to say "further" and "faster" and "it's like a seal vacationing in Nepal" instead of linking us to a 400page paper that would require 10years of studying to understand.
At least that's just how i reconcile those mind-boggling revelations with my idiot's understanding.
The concept is difficult to explain because it is completely unlike anything we experience in day-to-day life. This tends to be case for all extremes of physics, like traveling at a significant percentage of the speed of light or dealing with the behavior of subatomic particles. Things like the fact that light can't go any faster even if you're moving toward the light source or pretty much everything we learn from the double slit experiment are pretty counterintuitive imo.
I think we can say that the unreconcilable difference is acceleration.
As a hypothetical, consider two objects a distance of 100 meters away from each other at time t=0, and 200 meters distance from each other at time t=1, where neither object is experiencing any acceleration and the perceived movement is straight away from each other.
If there is no spatial expansion, then they are moving away from each other at 100 meters per time unit.
If the change in distance is entirely up to space expanding, then space is doubling every time unit.
If we then look at time t=2, these two models will give different predictions.
In the velocity model, the velocity remains constant and we expect to see the objects 300 meters apart, and measure a speed of 100 meters per time unit.
In the spatial expansion model, we expect space to continue expanding in proportion to itself, so double the distance again so that the objects are 400 meters apart, and the distance between them to be increasing by more than 100 meters per time unit.
In essence, it's the difference between a linear and exponential distance prediction when under no acceleration.
This reminds me of an interesting paper I came across a few years ago, that instead of having the Universe expand, with its spacetime increasing (being a bit vague here, to prevent it getting too math heavy), but instead turning it around:
Instead, have all particles shrink. This would be done with having all the constants change with time.
You would effectively still get the same results. It would still appear to us as if the Universe is expanding due to everything shrinking. Really, there isn't any good reason to prefer one model or the over except that expansion is a bit easier to understand for our brains. Which, frankly, the Universe doesn't care about. It's not very different from picking a different reference frame.
I'm still not sure whether I find it brilliant, trivial, or both.
So in one hypothesis you leave everything as is except one value (amount of space-time), while in the other hypothesis you leave that value alone and instead have literally every fundamental constant be variables instead.
I know which hypothesis I find more convincing and I think Mr. Occam would agree with me.
Except that they would be tied together, it's not as much as that you change every single variable in a perfect fit. It does not require all particle masses to be changed perfectly, as the ratios remain constant. Occam's razor doesn't really prefer one or the other if you ask me.
It's not about them being tied together or not, it's about them not being constant.
Before Einsteins theories of relativity, we assumed both space, time and all other fundamental constants of the universe to be, well, constant.
With the "typical" model of inflation by increasing the "amount" of space-time, we only change 3 of our assumptions: space and time are not constant and are actually intrinsically linked like electromagnetism.
For the "shrinking" model to work, the 19 known fundamental constants (according to Wikipedia) would all have to be indeed be changeable and would had to have changed in precisely such a way that the universe as we know it would even be possible.
It's simply that the number and severity of the different assumptions is vastly different while both explanations are coming to the same result, which is precisely one of the prime examples of where Occam's razor should be used.
So I have to confess: my earlier comments was kinda oversimplified, and I was trying to expand on to that. Then, I began to expand that in this comment, and now I'm conceding to your point, but not in the way I expected? This is going to be an unusual format for an Internet comment, but let me first the comment that I wanted to put in:
"These are good points, and I think(emphasis here, I could be wrong here about what you're trying to communicate) that in a part its my fault and not necessarily the concept. Because despite what I said earlier, you can actually have the exact same amount of constants, but with different variables."
"I assume you know that in materials you can describe electrons both in position-time space and energy-momentum space? What I talked about is kind of like that. When you do that, sometimes you can end up with the same number of constants but different variables."
But then I realised a few things that don't hold up. First, your metrics would need to accommodate too. Making cosmological red-shift a bit of a mess. While it may technically not be adding extra assumptions to your model to get consistent results, it's a bit like putting extra coordinate transformations in Maxwell's equations and seeing it's equally valid. It kinda is, but it doesn't make sense to treat it as equal per se. And while I can't rule out future discoveries for a shrinking model, it's a bit weird to do it now, apart from as an interesting thought experiment.
The second one is a bit more damning. Inflation and dark energy. These two are already messy of its own, but then putting them in the context of this model gets weird. In the case of inflation you would have to add extra energy to changing the constants. Whereas with the position-time <-> energy-momentum switch you can, in a pure mathematical sense, get around it, I don't think you can do that with inflation? It's been years since I took my course in cosmology so I'm looking over some papers of it, but unless you make the potential of the inflation time dependent it just won't work?
And inflation already being (more or less) born out of Occam's razor, it would be weird to adjust it like that... as a counterargument against Occam's razor. This contradicts my earlier statement pretty thoroughly. And even if there is a mathematical workaround... I don't think that could survive dark energy at the same time.
There is probably more but I think it's one of those things you can't really dig your way out to unless something big changes in Cosmology. Not impossible, but unlikely. Anyway, you're right, it can't really survive Occam's razor. At least, not in a way I can't argue against it.
As a matter of fact I did not know of the two ways that you can describe systems, so thank you very much for mentioning and linking to it!
Also, considering you actually have taken courses in cosmology, you most definitely know way more on the topic (and more in depth as well) than I do. I'm just a layman with ADHD and too much time on his hands from time to time, which leads me to know a little bit about a lot of things.
So I freely admit that I wasn't entirely able to follow the depths of the latter half of your comment, but that's entirely on me for not having the prerequisite knowledge and understanding of the topics being discussed.
What I do entirely agree with is that the shrinkage scenario could become much more likely should some new discoveries change our understanding of cosmology. But for now, it unfortunately falls under Occam's razor.
Thanks again for your very interesting and informative comment!
It is hardly Mr. Occam's fault that we picked length, the one fleeting thing in our universe [according to RC's hypothesis], as the unit we base almost all of our other units on. It's literally the metric system. As in meter. We picked a unit of length and made everything depend on that.
You could perfectly well define lengths via the hubble constant. It would be a brain-melting system of units to work with, but not because it is inherently more complex, just more convoluted for human intuition. If my intuition is right, defining lengths via hubble's constant (or an adjecent concept perhaps) would give you the system of units where the constants are constants again. Perhaps they're all constant factors of this one other constant that changes with time.