# How does matter form into galaxies during the cooling down period?

• Fabo
In summary, the conversation covers topics related to quantum mechanics, relativity, and the concept of absolute speed. The participants discuss the scales at which these theories are relevant, the concept of the speed of the universe, and the limitations of our understanding of the universe. There is also mention of the uncertainties and unknowns in theories such as evolution.
Fabo
Hi

Im new here, and have begun to read this book. I don't have any science qualification but I've read a few books on evolution. I'm making notes as I go along and here are 2 difficulties I have.

1) It says gravity is for large scale and quantum is at the small scale. I am just wondering what are the scales relative to ? I would have thought size is relative ?

2) It says there is no absolute speed, however surely the guy on the train's speed is = speed of train + speed of Earth + speed of Milky Way + speed of Universe. His eyes tell him he's not moving (if he doesn't know he's on a train) but our eyes didnt evolve to read accurate speeds , certainly not at a planetary level so I don't agree that different observers are just as right as each other. I don't know if that make sense but if you assume the universe is moving in relation to a nothingness , then there is an absolute speed.

Thats as far as I've got so far, just finishing off the chapter on Relativity , it is very interesting stuff.

1) Quantum effects are generally only significant at the atomic level and smaller. Gravity is generally only important where one of the things is at least as big as a mountain and the other is at least big enough to see.

2) There is nothing we can measure the speed of the Milky Way against, and the concept of the speed of the universe doesn't make sense, so the furthest you can go is the speed of the train relative to the centre of the Milky Way. As you read more about relativity you will find out why.

Ofcourse you could use relativity to measure some absolute speed as against the speed of the universe but the problem here is we don't even know how big the universe is because the speed of light permits us to see further then some distance x.So if we don't know the end of the universe nor do we know what's "outside" of it if there even is such outside then talking about some absolute speed is useless all we can do is talk about speed of object x versus speed of object D etc.All we are doing actually is comparing speeds from different objects to different other objects and or backgrounds.

And by the way be careful with all that evolution theory and everything that surrounds it as some areas of it are not as known as others , there are many unknowns etc , so you have to have a pretty good background and critical thinking to understand all the facts and all the parts which are still just a good guess. That makes a huge difference as there are things we know for sure (have measured them or made experiments) and things which we are not so sure but we have a say good guess or as science calls it level of certainty.

MrAnchovy said:
2) There is nothing we can measure the speed of the Milky Way against, and the concept of the speed of the universe doesn't make sense, so the furthest you can go is the speed of the train relative to the centre of the Milky Way. As you read more about relativity you will find out why.

We can measure the velocity of the Milky Way against the Cosmic Microwave Background. It turns out to be on the order of 550 km/s in a particular direction. See http://arxiv.org/abs/astro-ph/9312056 .

voko said:
We can measure the velocity of the Milky Way against the Cosmic Microwave Background. It turns out to be on the order of 550 km/s in a particular direction. See http://arxiv.org/abs/astro-ph/9312056 .

Yes it was a bad answer (although the figure for 550km/s is not the right one for the Milky Way's motion I believe). We can measure the our speed relative to the universe, but (I assume that) the reason Hawking says there is "no such thing as absolute speed" is that someone else moving (very rapidly) relative to us would measure us as having a different speed.

Fabo said:
2) It says there is no absolute speed, however surely the guy on the train's speed is = speed of train + speed of Earth + speed of Milky Way + speed of Universe.

And what is that "speed of the universe"? How do you measure it, how do you assign a value to it, what does it mean?

To see the problem more clearly, let's try writing out your sum without skipping the details:

Speed = Speed of train relative to Earth + speed of Earth relative to milky way + speed of Milky way relative to universe + speed of universe relative to ?

Nugatory said:
And what is that "speed of the universe"? How do you measure it, how do you assign a value to it, what does it mean?

To see the problem more clearly, let's try writing out your sum without skipping the details:

Speed = Speed of train relative to Earth + speed of Earth relative to milky way + speed of Milky way relative to universe + speed of universe relative to ?

Yes, well it depends what's outside the universe, it could be nothingness, or the universe itself could be contained in something that is moving also, so we get into a kind of Russian doll scenario. Actually it would be an arbitrary and self-satisfying thing on our part to assume the universe is not contained in something , its akin to Aristotle putting the Earth in the centre of the universe. So most likely its contained in a multi-verse thing, which brings me back to my first point. What exactly is size relative to ? Could our universe just be a part of an atom making up a much larger universe ?

Then there is the question what exactly is the definition of universe since we can't see the end of it.

Fabo said:
Actually it would be an arbitrary and self-satisfying thing on our part to assume the universe is not contained in something , its akin to Aristotle putting the Earth in the centre of the universe.

Self satisfying? I think it's simply one of several possibilities.

So most likely its contained in a multi-verse thing, which brings me back to my first point. What exactly is size relative to ? Could our universe just be a part of an atom making up a much larger universe ?

There is very very little to be gained from this type of discussion. It's more philosophical than anything else. To the best of our knowledge there is only one universe and the concept of something being "outside" the universe, or our universe "within" another, is not a scientific one since we have no way of knowing if it is true or false, even in principle.

"What exactly is size relative to ?"

I think this part of it is a very profound question deep in the center of physics.
It seems very interesting that the principals of interaction change with the size of the actors.
It lends a sense of "absolute size" to a field where absolute time and absolute space don't exist.
Right now it seems that "size" seems to be relative to the theories with which these things are described.

Well it's probably wise to scale something to the smallest size we have (Planck) rather than the biggest possible out there which we don't know of because we have no way of knowing that...

Drakkith said:
Self satisfying? I think it's simply one of several possibilities.

well humans are good at thinking they are special, their planet is special, their universe is special etc etc, and science has proved them wrong every time , but yes we have no way at the moment of testing it.

bahamagreen said:
"What exactly is size relative to ?"

I think this part of it is a very profound question deep in the center of physics.
It seems very interesting that the principals of interaction change with the size of the actors.
It lends a sense of "absolute size" to a field where absolute time and absolute space don't exist.
Right now it seems that "size" seems to be relative to the theories with which these things are described.

This is what I am getting at and you've put it very nicely. One thing that should not be absolute is size, just because something is "small" to us , doesn't mean it should be defined scientifically as small. If a creature evolved to see at the atomic level , then atoms wouldn't look too small to it.

Fabo said:
well humans are good at thinking they are special, their planet is special, their universe is special etc etc, and science has proved them wrong every time , but yes we have no way at the moment of testing it.
Which is why people tend to have trouble letting go of the concept of absolute speed. The best that can be said about it is that it is unnecessary. If it doesn't affect my ability to play table tennis on a train, it has no value and can be discarded as superfluous.

1 person
There is an absolute size: Atoms. An atom of any given element (at low energy state) can only ever be one fixed size. You can put energy in and make the atoms occupy higher orbits, but these are also a fixed and limited set of sizes. Anything smaller than a hydrogen atom can't be an element.

Fabo said:
well humans are good at thinking they are special, their planet is special, their universe is special etc etc, and science has proved them wrong every time , but yes we have no way at the moment of testing it.
No it is YOU that is making the anthropocentric assumption by insisting that our universe exists in the same spatial dimensions as every other universe (in order for the notion of speed within a multiverse to make sense). Most people that have given this serious thought realize that there is no reason for this to be the case, and that is why we say that "speed relative to the multiverse" has no meaning, not because we are denying the possibility of the existence of other universes.

bahamagreen said:
It seems very interesting that the principals of interaction change with the size of the actors.
Nobody is saying this. What changes with the size of the actors is the SIGNIFICANCE of different interactions. Within an atom, gravity is insignificant but quantum mechanics and other interactions become important. When you throw a ball in the air, nothing really matters except gravity and air resistance.

Algr said:
There is an absolute size: Atoms. An atom of any given element (at low energy state) can only ever be one fixed size. You can put energy in and make the atoms occupy higher orbits, but these are also a fixed and limited set of sizes. Anything smaller than a hydrogen atom can't be an element.

and what is an atom composed of ?

I have just finished reading the book and have made a few notes along the way. An interesting incident happened as I

I had been cooking bacon on a pan, and after eating I poured boiling hot water into the pan. I then came back later
to clean up and noticed that the grease had coalesced into shapes. Not just any old shapes, but perfect circles
of various sizes. The circles had grouped together, without touching, into clusters.

I realized that as the hot water had cooled down, matter on the pan had started to break up and form into circular shapes.
Some circles were huge, 10 or 12 times the size of other ones. But the most common size was about the size of the head
of a needle. Around the edges of the pan was the greatest concentration of circles.

We think that the early conditions of the universe were much the same, very hot and then a cooling down period. (which is still happening?) Matter that was scattered during the big bang formed into circles, which then formed clusters called galaxies. I can't replicate the effects
of gravity although I did notice some movement in the pan early on due to currents caused by the change in temperature in the water.

So in my frying pan I replicated more or less the early conditions of the universe !

## 1. What is "A Briefer History of Time" about?

"A Briefer History of Time" is a book written by physicist Stephen Hawking and co-authored by Leonard Mlodinow. It is a simplified and updated version of Hawking's earlier work, "A Brief History of Time", which explores the history and theories of the universe, from the Big Bang to black holes and the search for a unified theory of physics.

## 2. Is "A Briefer History of Time" meant for non-scientists?

Yes, "A Briefer History of Time" is written in a way that is accessible to non-scientists. Hawking and Mlodinow use clear and straightforward language to explain complex scientific concepts, making it a great read for anyone interested in learning about the universe.

## 3. What makes "A Briefer History of Time" different from "A Brief History of Time"?

"A Briefer History of Time" is a condensed version of "A Brief History of Time". It includes updated information and new theories that have emerged since the original book was published in 1988. It also uses simpler language and includes helpful illustrations to make the content more understandable to a wider audience.

## 4. Do I need to have a background in physics to understand "A Briefer History of Time"?

No, you do not need to have a background in physics to understand the concepts in "A Briefer History of Time". The authors do a great job of breaking down complex ideas and explaining them in a way that is easy to grasp for readers of all levels.

## 5. Does "A Briefer History of Time" offer any new insights or theories?

Yes, "A Briefer History of Time" includes new information and theories that have emerged since the original publication of "A Brief History of Time". This includes updates on the search for a unified theory of physics, as well as discussions on the origins of the universe and the potential existence of parallel universes.

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