Seeing the Universe, or an atom....

[Halbhh]

An nice updated version of the old video from way back in the late 70s, Powers of Ten, to help us visualize how big the Universe is, and more.

(remember as you watch, each ring is ten times wider across(!)...)

 

[Halbhh]

Here's the 1977 version, which is still pretty effective.

 

[FrumiousBandersnatch]

Here's the latest version of 'Scale of the Universe 2' - you can use the mouse scroll wheel to zoom, and it has labelled example objects for each scale.

 

[partinobodycular]

Here's the latest version of 'Scale of the Universe 2' - you can use the mouse scroll wheel to zoom, and it has labelled example objects for each scale.

Now all we need is the same type of animation for time.

Personally I like to imagine all of time and space as nothing more than a virtual particle popping in and out of existence. Here one instant and gone the next.

It's all relative.

 

[FrumiousBandersnatch]

Personally I like to imagine all of time and space as nothing more than a virtual particle popping in and out of existence. Here one instant and gone the next.

Nice idea... in a multiverse, that would give you a 'cosmic foam' of universes

It's all relative.

But what can the universe (all there is) be relative to?

 

[partinobodycular]

But what can the universe (all there is) be relative to?

Lacking an external scalar could the universe be described as being both infinitely big and infinitely small at the same time? And wouldn't any object within that universe be itself both infinitely big and infinitely small?

 

[sjastro]

Lacking an external scalar could the universe be described as being both infinitely big and infinitely small at the same time? And wouldn't any object within that universe be itself both infinitely big and infinitely small?

The observable universe is finite, the entire universe may be infinitely large if the density parameter
Ω₀ = 1 indicating the universe is flat.

The current value is Ω₀ = 1.00 ± 0.02 suggesting this is the case, although topologists (mathematicians who think donuts and coffee cups are one in the same thing) think the universe could be torus shaped.
Cosmologists however think this is unlikely.
Why The Universe Probably Isn’t Shaped Like A Donut

 

[Halbhh]

Lacking an external scalar could the universe be described as being both infinitely big and infinitely small at the same time? And wouldn't any object within that universe be itself both infinitely big and infinitely small?

This physicist writer below is usually good at bringing together a lot in a clear written way:
What Is The Smallest Possible Distance In The Universe?

 

[Halbhh]

Lacking an external scalar could the universe be described as being both infinitely big and infinitely small at the same time? And wouldn't any object within that universe be itself both infinitely big and infinitely small?

I was looking at that article I just gave you yesterday about the reasonable (but unproven) theory (using known observables, what we see in nature) about the very plausible possibility there is a 'smallest possible length' that can exist (in this Universe, that is, in this physics), and realized it might not be that clear without a background in modern physics (even though the writer is quite capable generally), so here's another:

NOVA | PBS --
Are Space and Time Discrete or Continuous?

See, it may be that 'reality' -- that is, physics, aka 'nature' -- might very well have a discrete (aka 'quantized') shortest possible length, determined by nature itself (that is, by this physics we have here in this Universe (the Universe is simply (entirely) just 'physics in action').

This would of course answer your question about scale, in that scale would then be determined in a final and absolute way by this very physics (this 'nature', aka 'Universe') we are in -- so that there is an absolute reference for the scale, and it's only an aspect of physics. So, in a sense then, objects like protons and galaxies would show then part of the fixed range of that absolute fixed scale, which would not be arbitrary (but locked down to a fixed range from the minimum possible length up to the total extent of the Universe).

 

[FrumiousBandersnatch]

Lacking an external scalar could the universe be described as being both infinitely big and infinitely small at the same time? And wouldn't any object within that universe be itself both infinitely big and infinitely small?

I suppose it depends what these terms mean - infinitely big usually means something along the lines of continuing indefinitely - scale would be irrelevant. Infinitely small implies a zero-dimensional point, which can't be our 4D spacetime. ISTM that the speed of light gives us a reference scale of sorts within the universe.

Roger Penrose's 'Conformal Cyclic Cosmology' is probably relevant - as the universe continues to expand, eventually all matter and particles will decay to a thermal background indistinguishable from that of quantum vacuum fluctuations and the concept of scale will become meaningless, so he suggests that this scaleless state can itself become the seed of a new big bang - or something... Apparently, the maths seems to work out, given certain assumptions

 

[FrumiousBandersnatch]

I was looking at that article I just gave you yesterday about the reasonable (but unproven) theory (using known observables, what we see in nature) about the very plausible possibility there is a 'smallest possible length' that can exist (in this Universe, that is, in this physics), and realized it might not be that clear without a background in modern physics (even though the writer is quite capable generally), so here's another:

NOVA | PBS --
Are Space and Time Discrete or Continuous?

See, it may be that 'reality' -- that is, physics, aka 'nature' -- might very well have a discrete (aka 'quantized') shortest possible length, determined by nature itself (that is, by this physics we have here in this Universe (the Universe is simply (entirely) just 'physics in action').

This would of course answer your question about scale, in that scale would then be determined in a final and absolute way by this very physics (this 'nature', aka 'Universe') we are in -- so that there is an absolute reference for the scale, and it's only an aspect of physics. So, in a sense then, objects like protons and galaxies would show then part of the fixed range of that absolute fixed scale, which would not be arbitrary (but locked down to a fixed range from the minimum possible length up to the total extent of the Universe).

In standard QM spacetime isn't quantized, but it's possible that in a complete theory of quantum gravity it could be.

 

[Ophiolite]

The thing I like about this thread is that no one is pushing an agenda, no one is claiming science is full of lies, that scientists are trying to prove God doesn't exist, but rather we have some interesting ideas, respectfully submitted and then nicely complemented by additional material. All in all what discussions on a science forum should be like and, from my perspective, a nice early Christmas present. So thank you to all who have participated and a Winner icon to each of you.

 

[Halbhh]

In standard QM spacetime isn't quantized, but it's possible that in a complete theory of quantum gravity it could be.

Are you trying to ask me what I think on whether space will turn out to be quantized? While we can't conclude that yet, I'd guess that we will learn that in time. (Do you have a degree in physics or such (like me), or a long time background of reading in the field?)

 

[FrumiousBandersnatch]

Are you trying to ask me what I think on whether space will turn out to be quantized?

Not really, just putting it out there; comment if you like.

While we can't conclude that yet, I'd guess that we will learn that in time. (Do you have a degree in physics or such (like me), or a long time background of reading in the field?)

No physics qualification, just a long-term interest. My comments are based on what I've read and heard from authorities I respect, so mostly not original thinking on my part.

 

[sjastro]

If spacetime is quantized it spells problems for quantum field theories which are the most successful theories known in physics.
Spacetime is continuous in quantum field theories which combines special (not general) relativity with quantum mechanics.
The energy-time Heisenberg uncertainty principle states;

ΔEΔt ≥ h/4π

ΔE is the uncertainty in the measured energy values which are eigenvalues of the Hamiltonian operator H in the equation H|ψ>= E|ψ> where |ψ> is an eigenvector.
The energy levels E are not continuous but discrete.
There is no quantum mechanical time operator T such that T|ψ> = t|ψ>.
In this case Δt is a time interval and not discrete or quantized.
If time is not quantized then neither can spacetime.

Cosmology uses general relativity as the theory for gravity where spacetime is continuous.

Are Space And Time Quantized? Maybe Not, Says Science

 

[Halbhh]

If spacetime is quantized it spells problems for quantum field theories which are the most successful theories known in physics.
Spacetime is continuous in quantum field theories which combines special (not general) relativity with quantum mechanics.
The energy-time Heisenberg uncertainty principle states;

ΔEΔt ≥ h/4π

ΔE is the uncertainty in the measured energy values which are eigenvalues of the Hamiltonian operator H in the equation H|ψ>= E|ψ> where |ψ> is an eigenvector.
The energy levels E are not continuous but discrete.
There is no quantum mechanical time operator T such that T|ψ> = t|ψ>.
In this case Δt is a time interval and not discrete or quantized.
If time is not quantized then neither can spacetime.

Cosmology uses general relativity as the theory for gravity where spacetime is continuous.

Are Space And Time Quantized? Maybe Not, Says Science

Yes. And....as Siegel explains at the smallest scale,
" If we decide to go down to below about 10^-35 meters ⁠— the Planck distance scale ⁠— our conventional laws of physics only give nonsense for answers....

"If you start attempting to perform quantum field theory calculations at or near the Planck scale, you no longer know what type of spacetime to perform your calculations in. Even in quantum electrodynamics or quantum chromodynamics, we can treat the background spacetime where these particles exist to be flat. Even around a black hole, we can use a known spatial geometry. But at these ultra-intense energy, the curvature of space is unknown. We cannot calculate anything meaningful.

"At energies that are sufficiently high, or (equivalently) at sufficiently small distances or short times, our current laws of physics break down. The background curvature of space that we use to perform quantum calculations is unreliable, and the uncertainty relation ensures that our uncertainty is larger in magnitude than any prediction we can make. The physics that we know can no longer be applied, and that’s what we mean when we say that “the laws of physics break down.”
What Is The Smallest Possible Distance In The Universe?

 

[sjastro]

Yes. And....as Siegel explains at the smallest scale,
" If we decide to go down to below about 10^-35 meters ⁠— the Planck distance scale ⁠— our conventional laws of physics only give nonsense for answers....

"If you start attempting to perform quantum field theory calculations at or near the Planck scale, you no longer know what type of spacetime to perform your calculations in. Even in quantum electrodynamics or quantum chromodynamics, we can treat the background spacetime where these particles exist to be flat. Even around a black hole, we can use a known spatial geometry. But at these ultra-intense energy, the curvature of space is unknown. We cannot calculate anything meaningful.

"At energies that are sufficiently high, or (equivalently) at sufficiently small distances or short times, our current laws of physics break down. The background curvature of space that we use to perform quantum calculations is unreliable, and the uncertainty relation ensures that our uncertainty is larger in magnitude than any prediction we can make. The physics that we know can no longer be applied, and that’s what we mean when we say that “the laws of physics break down.”
What Is The Smallest Possible Distance In The Universe?

The problem with quantum field theories is the excitations in the field lead to "point size" particles which are less than the Planck scale 10⁻³⁵ m and lead to infinities in the calculations.

A classical physics example can show why this is a problem.
The electromagnetic mass mₑₘ of a charged particle is defined as;

If the particle is point sized rₑ → 0 and mₑₘ → ∞ is a nonsensical answer.

The saving grace for a quantum field theory such as quantum electrodynamics is the interaction between charged particles leads to a resonance where the point size particles behave as particles of a finite size beyond the Planck scale.
As a result scales approaching the Planck scale can be ignored in the calculations and quantum electrodynamics is known as a renormalizable theory.

Unfortunately a quantum theory for gravity is not renormalizable which is why String theory is of interest amongst physicists where the point size particles of quantum field theories are replaced by strings which make String theory renormalizable.

 

[Halbhh]

The problem with quantum field theories is the excitations in the field lead to "point size" particles which are less than the Planck scale 10⁻³⁵ m and lead to infinities in the calculations.

A classical physics example can show why this is a problem.
The electromagnetic mass mₑₘ of a charged particle is defined as;

If the particle is point sized rₑ → 0 and mₑₘ → ∞ is a nonsensical answer.

The saving grace for a quantum field theory such as quantum electrodynamics is the interaction between charged particles leads to a resonance where the point size particles behave as particles of a finite size beyond the Planck scale.
As a result scales approaching the Planck scale can be ignored in the calculations and quantum electrodynamics is known as a renormalizable theory.

Unfortunately a quantum theory for gravity is not renormalizable which is why String theory is of interest amongst physicists where the point size particles of quantum field theories are replaced by strings which make String theory renormalizable.

We keep hearing of string theory not coming through, not achieving something, over the years. Here's a sharp take on it: Why String Theory Is Still Not Even Wrong

I notice another overview -- maybe Siegel would be more neutral (I've not read yet):Why String Theory Is Both A Dream And A Nightmare

 

[Halbhh]

The problem with quantum field theories is the excitations in the field lead to "point size" particles which are less than the Planck scale 10⁻³⁵ m and lead to infinities in the calculations.

A classical physics example can show why this is a problem.
The electromagnetic mass mₑₘ of a charged particle is defined as;

If the particle is point sized rₑ → 0 and mₑₘ → ∞ is a nonsensical answer.

The saving grace for a quantum field theory such as quantum electrodynamics is the interaction between charged particles leads to a resonance where the point size particles behave as particles of a finite size beyond the Planck scale.
As a result scales approaching the Planck scale can be ignored in the calculations and quantum electrodynamics is known as a renormalizable theory.

Unfortunately a quantum theory for gravity is not renormalizable which is why String theory is of interest amongst physicists where the point size particles of quantum field theories are replaced by strings which make String theory renormalizable.

Ah, here's something interesting, which I'll put on my read-soon list:
https://www.quantamagazine.org/the-...of-physics-that-only-math-can-solve-20210610/