space questions

[BlueBearBoots]

Thanks read quite a lot of that thread most quite difficult to understand but one paragraph I thought explained quite a lot, one of yours I believe -




"Again it seems like one of these human-appealing ideas and then physics sticks two fingers up at us and tells us the universe doesn't work how we'd like it to, it works how it does. "

 

[denislawsbackheel]

We don't know how far the edge of the universe is from us.

The edge of the observable universe is about 13 billion light years away.

That means the oldest light we have detected from stars are that far from us. Doesn't mean there isn't stuff beyond that though.

Actually the edge of the observable universe is about 46 billion light years away due to the expansion of space, even though the universe is only 13 billion years old.

I can't do the maths for that but what speed is the expansion happening at then?

In the first fractions of a second of the universe it expanded at many multiples of the speed of light.

 

[west didsblue]

In the first fractions of a second of the universe it expanded at many multiples of the speed of light.

You're right. During the period of super rapid expansion when the universe grew in size from a singularity to about the size of a grapefruit in the first 10[super]-32[/super] of a second after the big bang, the universe expanded at around 10 billion trillion times faster than the speed of light, although at that point in time, there was no such thing as light. The first photons didn't start to appear until about 1 second later by which time the universe was bigger than the solar system.

 

[Lavinda Past]

In the first fractions of a second of the universe it expanded at many multiples of the speed of light.

You're right. During the period of super rapid expansion when the universe grew in size from a singularity to about the size of a grapefruit in the first 10[super]-32[/super] of a second after the big bang, the universe expanded at around 10 billion trillion times faster than the speed of light, although at that point in time, there was no such thing as light. The first photons didn't start to appear until about 1 second later by which time the universe was bigger than the solar system.

That has well fucked up my nut man.

I have trouble understanding how something Mrs Lavinda ordered at 21:59 on Monday night can be delivered to our house less than 12 hours later. Do these people sit around just waiting for her to order things?

 

[Skashion]

There is no issue with the universe expanding faster than light. It doesn't break any laws of physics.

 

[dazdon]

There is no issue with the universe expanding faster than light. It doesn't break any laws of physics.

But if the speed of light is the fastest speed of travel how can something travel faster?

Genuine question.

If two things travel as fast as the speed of light in opposite directions is that twice the speed of light?

 

[west didsblue]

There is no issue with the universe expanding faster than light. It doesn't break any laws of physics.

But if the speed of light is the fastest speed of travel how can something travel faster?

Genuine question.

If two things travel as fast as the speed of light in opposite directions is that twice the speed of light?

Nothing is travelling faster than light. The space between two distant objects is itself rapidly expanding causing the distance to increase at a rate faster than the speed of light but the objects themselves are not travelling faster than light.

If two things are travelling in opposite directions at a speed approaching light speed, the relative speed of one from the point of view of the other is still not faster than the speed of light due to time dilation (per Einsteins theory of special relativity).

 

[york away to this!]

In the first fractions of a second of the universe it expanded at many multiples of the speed of light.

You're right. During the period of super rapid expansion when the universe grew in size from a singularity to about the size of a grapefruit in the first 10[super]-32[/super] of a second after the big bang, the universe expanded at around 10 billion trillion times faster than the speed of light, although at that point in time, there was no such thing as light. The first photons didn't start to appear until about 1 second later by which time the universe was bigger than the solar system.

That has well fucked up my nut man.

I have trouble understanding how something Mrs Lavinda ordered at 21:59 on Monday night can be delivered to our house less than 12 hours later. Do these people sit around just waiting for her to order things?

the simple answer is that the scheming woman orders these things weeks in advance then, as it approaches D-day (delivery day) she wanders by, bending down to pick a piece of fluff off the carpet, wriggles those hips then asks nonchalantly "would you mind if I ordered one of those thingamywhatsits, dharling?" You're just too close to the action and too engrossed to notice the reality...

 

[Skashion]

There is no issue with the universe expanding faster than light. It doesn't break any laws of physics.

But if the speed of light is the fastest speed of travel how can something travel faster?

Genuine question.

If two things travel as fast as the speed of light in opposite directions is that twice the speed of light?

Space doesn't expand from some edge, outwards. It expands from all points in all directions. It does this at a rate of 67.8 kilometres per second per megaparsec which is very very slow and is a tiny tiny fraction of the speed of light. However, over an immense distance it accumulates. I did back of a fag packet calculations and found it was about 14,4 billion light years. Anything further away than that, and we will never see it because anything beyond is moving away from us faster than the speed of light, even though the objects themselves aren't moving anywhere near that speed. Think of it like an escalator. You don't move, the stairs do and each individual step is playing some part in moving you a greater distance than one single step.

Nothing is moving faster than the speed of limit in its own frame of reference (itself basically). Two spacecraft moving in opposite directions have precisely fuck all to do with each other as to measuring their individual velocities and relative velocities have nothing to do with why the speed of light and why it can't be broken. As a vector you could measure it like that but no laws of physics are being broken. The speed of light is a very very real thing. It's about as tested as it's possible to be. It's not theory like some people seem to think. Just because we don't have spacecraft that can do it doesn't mean we aren't sure. We throw things in particle accelerators at 99.999999% of the speed of light all day every day so we know exactly what happens. They get heavier and heavier and that means it takes more and more force to accelerate them. So all we do is keep adding yet more 9s after the decimal point. We're not making this shit up. We know things with rest mass cannot be accelerated faster than the speed of light or we'd be doing it.

If two things are travelling in opposite directions at a speed approaching light speed, the relative speed of one from the point of view of the other is still not faster than the speed of light due to time dilation (per Einsteins theory of special relativity).

That's not true. There is no issue with the relative velocities being higher than the speed of light. Time dilation is only significant at extremely high fractions of the speed of light because it's highly logarithmic. At say a relative velocity of 1.5c time dilation would be nowhere near significant enough to bring it below 1c.

 

[west didsblue]

If two things are travelling in opposite directions at a speed approaching light speed, the relative speed of one from the point of view of the other is still not faster than the speed of light due to time dilation (per Einsteins theory of special relativity).

That's not true. There is no issue with the relative velocities being higher than the speed of light. Time dilation is only significant at extremely high fractions of the speed of light because it's highly logarithmic. At say a relative velocity of 1.5c time dilation would be nowhere near significant enough to bring it below 1c.

For a stationary observer watching both these things coming towards each other it is correct that the relative velocity of the two is greater than light speed, however I was making the point that from the point of view of one of the high speed objects travelling at close to light speed, the other one coming towards it at close to light speed would not be perceived as going faster than light due to Special Relativity.