Why do scientists think there was a big bang?

[A_Seagull]

If one compares the radial velocity of distant galaxies with their distance one finds that there is a strong correlation. The greater the distance the greater the velocity.

If one then projects backwards in time, the inference is that all the galaxies were at one place some 14 billion years ago.

The inference of a big bang occurring at that time would not seem unreasonable.

[Greta]

Funny old world, eh?

Indeed. You are quite right that it is a question of scale, but given the supposed initial dimensions of the universe, its growth in the first few seconds I think can reasonably be called explosive. But it is an interesting point that to any 'god' that could see the entire universe (or at least our part of it), it would be like watching a balloon being blown up for nearly 14 billion years.

It's an assumption to say that the growth was explosive, though, because that depends on the size of the universe.

Initial growth and development (state changes) is always more rapid than subsequent development. It's said that there was more change in the first second after the BB than in the 13.8b years afterwards. By the same token, Dawkins suggested that gastrulation (which is also a kind of eversion) is a more profoundly radical development than all subsequent development of an organism.

[-1-]

For time to exist there must be sumthin' that changes, not only as reference but as actual source (of time).

So: time is (the possible perception of and the possible measuring of) changing matter.

there must be sumthin' that changes, not only as reference but as actual source (of time): you are stating, as I understand, that change causes time.

I beg to differ. It's like saying objects cause length.

In my opinion time makes change possible.

Without time there is no change. But without change there is still time.

It's what allows what to happen. Time is independent in its passing from events. Events are not independent of time.

There are many more ways of saying this. Can I prove it? No. It's a matter of intuition.

[-1-]

Time is independent in its passing from events.

This is actually not true. While event still don't cause time, time is affected by events. The faster an object moves, the time aging it slows down.

[henry quirk]

Agreed. My intuition just doesn't agree with yours, is all.

[-1-]

Agreed. My intuition just doesn't agree with yours, is all.

But only one of us can be right (or neither of us).

Two men approach their village rabbi. Weiss says, "Kohen borrowed my hat and he did not give it back to me. He owes me five bucks." "You're right," says the Rabbi. Kohen says, "yes, but Weiss here owes me five bucks from last year. I don't owe him any money." "You're right," says the rabbi again. "But Rabbi!" says Weiss, "we can't both be rigth!" The rabbi looks at him perplexed, and says, "you're right!"

[-1-]

The above is one of my favourite philosophical jokes. It is good, because it plays on the violation of the law of the excluded middle, and yet, somehow, it still makes sense. A bit like an Escher-drawing that defies the simple laws of three-dimensional perspectives.

[Greta]

Time is independent in its passing from events.

This is actually not true. While event still don't cause time, time is affected by events. The faster an object moves, the time aging it slows down.

My understanding is that events allow us to define time.

Without orbits, rotations and radioactive decay, we would have to define time without circularity, as there'd be, for instance, permanent day and only one season. How would you work out when to meet a friend for lunch?

[gaffo]

And such symmetry-breaking really bothers me, it doesn't just happen without something causing it.

Gawd caused it of course

[gaffo]

But I approach the contents of the human mind from a largely electromagentic perspective and I may be wrong.

I also usually shake the contents well, having approached it from a distance, so the electromagentic colour does not bunch up.

https://archive.org/details/Mindwebs_23 ... ertion.mp3

[gaffo]

I rather like the notion that everything had its source in a point-singularity.

I also enjoy the idea that the Great Explosion is still going on, that we're ephemerals in the midst of it, thinkin' Reality is all stable and shit when -- really -- it's all in flux.

It's not nihilism, but it sure takes the edge off.

this only is apt if the universe is closed, it looks to be open.

also a BH singularity is not of the same nature as the "Singularity" of the Big Bang, the former still has a presence in our universe via its gravitational power, and BH remains in our universe, though it is in a way its own universe.

[gaffo]

From an article I was reading this morning:
https://www.quantamagazine.org/big-boun ... -20180131/

With a single initial ingredient (the “inflaton field”), inflationary models reproduce many broad-brush features of the cosmos today. But as an origin story, inflation is lacking; it raises questions about what preceded it and where that initial, inflaton-laden speck came from. Undeterred, many theorists think the inflaton field must fit naturally into a more complete, though still unknown, theory of time’s origin.

In terms of narrative, I currently prefer the idea of a "big birth", where a new universe may form from the void left by the last.

assuming your thesis (for discussion's sake ( I'm lightyears too dumb to understand Astrophystics)) is correct, then when the "big Rip" happens, there will be "enough void" to birth a new future universe in 15 billion years time.

[gaffo]

Probably too much emphasis is placed on what was originally supposed to be a joke name to mock the idea https://academic.oup.com/astrogeo/artic ... .28/302975. It's misleading.

What we have is a "big grow" at a rate that we perceive as overwhelming explosive force. I suppose if you are tiny enough, what might be slow growth for extremely big things would seem explosive. For instance, think of the Earth orbiting the Sun at 107,000 km/h. Pretty fast, right?

That's the Earth taking a whole hour to move about four to five times its own diameter. Imagine walking at three metres per hour. You would hardly seem to be moving. Yet that's four or five times the diameter of the most spheroidal person imaginable. For most of us the equivalent would be much less again.

Yet the Earth's imperceptibly slow ooze around the Sun is about thirty times the speed of our fastest jet flying over its surface. It's over forty times the speed of a bullet. The Earth's extremely slow orbit around the Sun is at an explosive speed to us tiny humans.

The Sun's speed around Sag A* of 828,000 km/h - less than a single of its own diameter in an hour - is a simply devastating speed for us, over 200km/s.

Bring this notion to a universal scale and, whatever the universe would be to itself (if it thinks), it would seem to be slowly growing like many things within it. However, what would be imperceptibly slow growth at a universal scale is perceived by entities of our scale as explosive inflation that exponentially dwarfs lightspeed.

Funny old world, eh?

you are refering to the Universes (WRT to us) "Event Horizon" where anything beyond 13.8 Lightyears is traveling faster than the speed of light and so invisible (and literally beyond the Universe (WRT to us)), due to expansion of space.

[gaffo]

I am uncomfortable with the notion that time started with the big bang. I either have a very impoverished ideation of what time is... it is not yet defined and / or discovered how and what time is. So how can people confidently say that "time started with the big bang"? It is a dimension, like a linear dimension in space, which exist whether there is matter in it there to define space, or not... time exists, whatever it is. It can't not exist, much like axes X, Y, and Z can't not exist in the three-dimensional coordiate system that can be used to describe point in space.

If someone here could please come forward and provide some sort of a descriptive explanation how time could not exist before it started with the big bang, I would be very appreciative. (While at the same time remaining critical of the notions and ideations presented.)

Time is the "fourth dimension"

and no - no one can explain how time could not existed 'before" the BB.

hell Physicists have been working on and failing at a Unified Theory for a Century!!!!!!!!! undestanding the nature of the BB and Time is above the not found yet Unified Theory!

so i would not expect an answer in the next millinia or more.

[gaffo]

We call it a bang, because it behaved like an explosion.

Well, there's no real analogue. Explosions as we experience them are chemical or nuclear reactions that stop once the fuel is exhausted. That more or less was the assumption behind some early interpretations, but as others have shown, it's not a very good model,

the model is fine, its the termonology that sucks.

explosions fly outward into already existing space.

BB did not do that, there was no space to explode out into.