Quote:
Originally Posted by MolsonInBothHands
Ok, no edges or center to the universe. 3 dimensions expanding into 4? The fourth dimension being time?
Are there images looking towards the perceived epicenter of the big bang?
If I put a performance chip into my truck which allows me to drive 78 billion light years an hour, (Only slightly faster than Deerfoot trail.) and I drove in one direction, where would I be in relation to my starting point after 1, 1.5, and 2 hours? Is there a screen wrap like in the game asteroids?
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There is no epicentre of the big bang. The closest answer would be to say it is where you are sitting, where I am sitting, anywhere and everywhere in the universe.
Time is not the fourth dimension I'm talking about. I'm talking about an actual fourth spatial dimension.
Nobody knows for sure, but like on the balloon, you just might end up where you started, over and over again. Of course it's kind of silly to think about since it's utterly impossible.
Quote:
Originally Posted by photon
When they talk about the radius of the universe, really they usually mean the radius of the "observable" universe. So the 78 billion light year radius thing just means that the light from the beginning of the universe that is reaching us now in combination with the expansion of the universe since the beginning works out to 78 billion light years.
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Okay, here's the deal with the 78 billion number. First, I need to introduce a thing called a
co-moving coordinate - this goes back to the balloon example. Imagine points on a piece of paper that can be stretched out. They have a fixed coordinate position. Now stretch the paper out evenly, and the points are farther apart. But they are farther apart in proportion to the amount stretched, and they are still exactly evenly spaced as they were to begin. They still reside on the same coordinates of the grid, it is simply the grid that has stretched. Coordinates like this are called co-moving coordinates.
The universe is 13.7 Gyr old.
Prima facie, the universe should be 27.4 Glyr (giga light year = billion light years) across. But it is not, it is 2x78=156 Glyr across. Why? Because what we are measuring are co-moving coordinates. Yes they are 78 Gyr away, but that is only cause the universe has stretched that much. 13.7 Gyr ago we were all in the same spot, but now the paper has been stretched out. The numbers on the grid have not changed. But we are not reading the numbers on the grid, we have our own biased numbers we write on the grid ourselves to measure the distance.
Here's a diagram:
Hope that's not too unclear. I realized I should have picked better numbers for the coordinates, but it was too late to change it in paint once I realized they were going to involve square roots. Oh well, the relation and the concepts are still there.
Quote:
Originally Posted by troutman
There are a hundred billlll-yun stars in the milky way galaxy, and a hundred billll-yun galaxies. (Carl Sagan)
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My idol.
