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This is an important question with a slightly surprising answer. First you need to understand that the Big Bang was not an explosion of matter into space, it w
by InclinedPlane 8y ago
This is an important question with a slightly surprising answer.
First you need to understand that the Big Bang was not an explosion of matter into space, it was an explosion of matter and space (technically space-time). This might be hard to wrap your head around, it might be easier to think about space-time as non-infinite, say curving back on itself like the surface of a balloon (though as far as we can tell it is infinite).
Second, during the early Universe just after the Big Bang when the energy density of the Universe was incredibly high the density was nevertheless incredibly uniform. So, let's say you are inside a soup of matter and energy with a density as high or higher than the core of a star, but there is matter in every direction, what way is gravity pulling you? This is the other non-intuitive bit, gravity isn't pulling you in any direction. Pick a volume of matter in space around you and consider how its gravity affects you, for every single volume there is a corresponding volume on the opposite side of you that has exactly the same mass and is exactly as far away from you, cancelling out the gravity from the first chunk. And this is true for every single bit of volume around you, there's a 1:1 mapping of bits of stuff around you with other bits of stuff on the opposite side of you which exactly counterbalances the gravitational force from the first bit. The gravitational field is uniform, so nothing collapses, no black holes form, no stars or planets form either.
It's only after the Universe continues to expand and minute variations in local density are gradually amplified (over millions of years) into denser and denser clumps that it becomes possible to form galaxies and galaxy clusters/super-clusters (and thus black holes).
Now, we don't know for sure whether or not there were isolated little "super clumps" of extra density in the early Universe which allowed for the formation of black holes prior to the formation of galaxies (so-called primordial black holes). That's one theory for explaining the existence of supermassive and especially ultramassive black holes, but it's unconfirmed. However, now it seems as though we have enough evidence to show that primordial black holes can't be the explanation for the evidence for dark matter.
- perl4ever 8y ago"First you need to understand that the Big Bang was not an explosion of matter into space, it was an explosion of matter and space (technically space-time)." This is a type of statement I have read many, many times, but to me, it's the same as saying "wakalixes!". I've never read anything that gave me a hint of why and how there should be a difference between two objects receding from each other and "space itself" expanding.
- ketralnis 8y agoNew space is being created between those two things. When they move 1 meter apart from each other through space, they'd move 1 meter back again to meet up. But when space itself is expanding between them, they've moved 1 meter apart but now to get back together they have to move 2 meters. This has some other subtler ramifications. It means that the space between the two objects can increase at faster than the speed of light (because you can't move through space faster than light, but space can expand faster than light). Also, with the Higg's field's nonzero rest value _energy can be created from nothing_ by creating space. Yes, this violates conservation of energy.
- kamaal 8y ago>>It means that the space between the two objects can increase at faster than the speed of light Say they are two objects in the universe A and B. New space is created between A and B faster than the speed of light. There is a USB drive carrying a dump of wikipedia on B. Does this imply information is now moving faster than the speed of light?
- danbruc 8y agoNo because the USB stick is going nowhere, it just remains at B. Imagine a tiled floor where A and B are the centers of two tiles, the USB stick also resting on the B tile. Expansion of space just means that you are constantly increasing the gaps between tiles maybe inserting new tiles every time the gaps become wide enough. The USB stick however just rests on the B tile not moving through space, i.e. reaching another tile, ever.
- kamaal 8y agoExplain to me how this works. A and B remain stationary while only new space gets created between them? By geometry, the shortest distance between two points is a straight line. If A and B are two stationary objects, with a straight line being shortest distance between them. Then space is basically a twisted thread like path between A and B, More thread is created every time instant 't' than light can travel through it? And if some one figures out a way to walk from A to B in a straight line then they can walk faster than anything that can walk on the thread?
- glandium 8y ago> And this is true for every single bit of volume around you ... except on the edges... but maybe there wasn't an edge and space is sphericalish? And if it was back then, why wouldn't it be now? Which brings the question: if you go far enough in one direction, do you come back where you started? Can we figure out whether that's the case?