New in cosmology and fundamental physics

I just began reading a few pages here after being away from this thread.

I have neither the expertise nor the interest in things widely considered unknowable. Which brings me to me comment regarding whether or not the universe is infinite.

To claim it cannot be, simply because there is no visible proof, is akin to flat earthers who have never seen the globe or climate deniers who's weather hasn't changed much.

The human eye, or even the human experience as a whole, is not the final arbiter or what is real and true and what isn't.

If the entire body of science agrees it is an unknowable, who but the self righteous would claim otherwise?

That's why I believe that intrinsic expansion (not acceleration!!!) of space is 90% certain to be right.

I just began reading a few pages here after being away from this thread.

I have neither the expertise nor the interest in things widely considered unknowable. Which brings me to me comment regarding whether or not the universe is infinite.

To claim it cannot be, simply because there is no visible proof, is akin to flat earthers who have never seen the globe or climate deniers who's weather hasn't changed much.

This is incorrect. We live in a Universe where information and ourselves are limited by the speed of light - a geometrical constraint rather than a "speed limit". That means at any point in time we only have information about a FINITE part of the Universe. We literally have no information about the rest of the Universe - we can only reasonably hypothesise about it - and you can't draw hard conclusions about something about which you have literally zero information.

It's worth emphasising that it is different to hypothesising the laws of physics are the same in the part of he universe we cannot see. This is an extrapolation which obeys Occam's razor. By contrast the rest of the Universe being finite or infinite are equally compatible with what we see.

It isn't acceleration btw. Again missing the point, but misleading since expansion of all space obviously involves acceleration of expansion.

This is simply false. It is the same as the (also false) statement "if two cars have a relative velocity, they are accelerating".

That SHOULD be obvious at least.

You should now see it is obviously false.

But the acceleration is not what would be intrinsic to space. It is the expansion which would be intrinsic.

I explained why that does not make sense.

Think of it as breeding and think of space as existing in quantum bits. Each quantum bit of space has a probability of duplicating in a set time.

This intuition is false (it is Galilean in nature, not that of modern physics). Volume is not Lorentz-invariant, so the idea of a frame independent "quantity of space" is inconsistent with empirical facts. If you move at a high speed, 2 liters of someone else's space can look to you like 1 liter.

That leads to acceleration of expansion, rather obviously,

Logically incorrect.

If a piece of string gets 1 meter longer every second, it is expanding but not accelerating. This suffices to disprove your inference that expansion implies acceleration.

You made an additional unstated assumption that the rate of expansion per length is constant. This is exponential expansion, while (classical, pre-dark energy) Hubble expansion is linear expansion (like the piece of string). The modern understanding is of a mixture - mostly linear but with acceleration becoming more significant over time. And the most modern understanding is that the amount of acceleration may be varying in a previously unexpected way.

but each bit of space is merely duplicating within a probability per unit of time. If you try to understand the effect that would create, @Elroch, you may then see how attractive such a proposition should be to any theoretician.

Pure exponential expansion as you describe is mathematically simple. It is also definitely not consistent with observation, where it took decades to detect divergence from LINEAR Hubble expansion (the 1998 result).

I believe there is no such thing as "dark energy" since expansion requires no energy at all, if it's an intrinsic property. Many theorists and scientists agree that dark energy probably doesn't exist. Where was it last spotted btW?

Expansion requires only kinetic energy! The reason most people believe in dark energy is a failure to explain empirical data without it. It is the divergence from simple linear expansion.

I explained above that "intrinsic expansion" is not a meaningful concept for space, because there is no distinction between it and "things moving apart". It's fundamentally like the fact that there is no such thing as "intrinsic (or absolute) velocity". All velocities are relative.

Mathematically the reason is that by stark contrast with Newtonian physics (with universal Euclidean space) and to a hypothetical world that is modelled precisely by a single special relativistic frame, the structure of space time we observe can be modelled as a manifold by patching together local inertial frames in an infinite number of ways. One of these ways can have all the galaxies stationary and the space expanding between them, another can has one galaxy moving through space away from another. The distances are all the same in both. The comoving representation is preferred one - the one in which all the local frames are stationary w.r.t. the cosmic microwave background. From this viewpoint the space expands.

But acceleration is different. Current understanding is that all remote galaxies are accelerating away from us. This is not something that can be brushed under the carpet with choice of frames. It has fundamental consequences beyond distances changing in a non-linear way. Most famous is the cosmological horizon, which means that for any distant galaxy we will never see it get past some fixed age. We will see it forever, but it will get more and more redshifted as it approaches this age when it "reaches the cosmological horizon". In addition, no physically possible motion from our location can see more of the galaxies future. This is because it is not a consequence of relative velocity - which could always be compensated for with motion, but acceleration which can (and it is believed does) lead to a relative velocity converging to the speed of light in a finite (remote) time.

The concept that the universe is not expanding into empty space but that space itself is expanding sounds like mental masturbation to me.

I don't agree with the 'equally compatible' part.
The assumption that the universe would be finite beyond what we see is arbitrary.
Why would there have to be a boundary or limit?
It looks like a mistake of hubris.
When the back of the moon couldn't be seen we didn't assume it wasn't there.
-------------------
Consider another species somewhere - far beyond the extreme redshift that we see.
They see their own 'big bang' but because they are near or at its edge - they see evidence of other big bangs also. In other locations.
They see our big bang. Their own. And one more.
So their cosmology communities all agree they can see three big bangs.
And some state: 'there are only three. we don't see any others and we can't measure them if they're out there so we don't care about those.'
Then rumour psychology kicks in.
'There are only three big bangs in the universe! Our's and two others!'
Somebody else says 'Cut it with the reifications. We see three. That doesn't mean there isn't an infinite number out there. Why shouldn't there be?'
Reply: 'We don't like physical infinity. We're cutting your funding.'

You may dispute whether galaxies are moving away from us, but objectively there is both a directly observable relativistic doppler red-shift AND the fact that they get smaller and smaller in terms of angle subtended. Also - and this is key - standard candles give distances rising with redshift. Note that we can't observe a single galaxy for long enough to see directly it has got further away, what we can see is that less red-shifted galaxies are observed to be nearer, with the best inference of this coming from the "standard candles" such as type 1a supernova.

The precise relationship between distance and speed is key evidence for testing cosmological models.

If you disagree with that, you are not arguing with me, you are arguing with the state of scientific knowledge. It's an important distinction! Things like the idea that galaxies are not really getting further away are very fringe positions, especially these days.

You're commenting on two people who seem to be having a meaningless argument so I snipped it. But I don't buy any of what you say either. For one thing, there wouldn't be intelligent life at the edge of the universe.

I accept that the existence of life is a probability function but if it has a probability of zero and that probability carries a high confidence factor, it isn't going to happen. Another thing is why should "another Big Bang" be detectable? If it's detectable it is part of this universe. I know you are using "Big Bang"to mean "universe" and it's just confusing things further in your own mind!

The very idea of infinity is as an abstract idea. As soon as it is translated into reality, an overload is caused. That isn't because we don't have the intellect to understand it. It is because an abstract concept is being used improperly.

It is only a consensus though. I can guarantee that there are theoreticians who agree with me. As I've mentioned, I was able to convince some of them 15 years ago.

Anyhow, on a thread like this if you insist on too close a conformity with current beliefs and doctrine you are guaranteed to lose those with the better minds. Even if they agree with you they aren't going to respect anyone arguing too hard for conformity since it is by creativity that we advance

"Its two other people who try to do that"..... Professor Plum in the library?? Miss Scarlet in the billiard room?

@Elroch
Regarding 'acceleration' its quite a general term. Could apply to many things.

Nope. acceleration is the second derivative of distance with respect to time. The acceleration can be relative - between two entities, but it can also be absolute, relative to an inertial frame. The latter relies on the fact that two inertial frames differ by a velocity alone.

If objects are getting further apart and the rate that they're getting further apart is increasing - whatever the interpretation is of what's causing them to get further apart - I think that could be called 'acceleration'.

That is the definition of (relative) acceleration.

The earth orbits the sun but that term 'orbits' would seem to be more useful than saying it 'accelerates' around the sun because its direction of motion is changing and therefore its velocity is changing which 'acceleration' refers to.

In this example, there is only acceleration in a Newtonian context. In a relativistic context, the Earth is always in an inertial frame with zero acceleration. In the former, the space is assumed flat (an approximation). In the latter the curvature of space-time is what makes it possible for the acceleration to be zero. A good way to think of it is that the Earth moves in the equivalent of a straight line (in curved space time).