How can space travel be like world travel?

[Janx]

These terms suggest seeing. And even if it isn't seeing light, it is detecting something farther away and further back in history than the universe has existed.
Bullgrit

think this effect is the "something wierd" physics.

I agree that if the universe is 14 billion years old, then the farthest anything could travel from the center is 14 billion light years, putting 2 objects at opposite sides as beingg 28 billion light years apart.

If we point a really great telescope at an object that is 45 billion LY away, that object is impossible unless something "special" has happened.

For one, the light from it can't have reached us yet, becuase the universe isn't old enough for it to have moved to be 45billion LY away.

Is some of the "special" that during the big bang, time went "faster" so matter could get spread out farther in less time? Is all the fuzzy speak because physicists don't want to admit that stuff went faster than the speed of light when measured with an absolute stopwatch outside of the universe?

Is the universe actually injecting space between objects, contributing to additional expansion, seperate from their natural movement as trajectories from the big bang?

If yes, then isn't our own solar system expanding?

If the solar system is expanding, what about the space between molecues or inside atoms?

 

[jonesy]

Trying again as the reply fractured oddly:

"Observable universe"
"Visible universe"
These terms suggest seeing. And even if it isn't seeing light, it is detecting something farther away and further back in history than the universe has existed.

Seeing what was. Not what is. You did say you understand time delay.

 

[Morrus]

Is some of the "special" that during the big bang, time went "faster" so matter could get spread out farther in less time? Is all the fuzzy speak because physicists don't want to admit that stuff went faster than the speed of light when measured with an absolute stopwatch outside of the universe?

Nope, it's expansion, not movement. Space is expanding; objects in it aren't moving (well, they are, but separately to the expansion).

Is the universe actually injecting space between objects, contributing to additional expansion, seperate from their natural movement as trajectories from the big bang?

The Big Bang doesn't have a central point; the whole universe IS the central point. So things don't have a trajectory away from one. Everything is moving away from everything, not just from us.

And yes, space is being created between objects. That's the whole "dark energy" thing, and we don't understand why yet.

If yes, then isn't our own solar system expanding?

Local gravity can overcome it, as I understand it. I'm a little fuzzy on that, but with the distances we're talking our solar system is teeny tiny and the amount of interjected space isn't enough to overpower the gravitational effects of the objects within that small area.

Even our local group of galaxies will tend to come together rather than move apart.

The amounts of space being created become massively significant when you're talking about billions of lightyears.

It's a matter of scale. Locally, gravity is pulling things together at a faster rate than space is expanding them away from us, so the net effect is that they come together. On a universal scale, with the vast, vast distances between objects, that's not the case because the amount of space being created in between them is much, much more - so gravity is pulling them together slower than they are being expanded away, with a net effect of things spreading apart.

If the solar system is expanding, what about the space between molecues or inside atoms?

The electromagnetic and nuclear forces are even stronger than gravity - much, much stronger. They're held together by immensely strong forces.

Magnetism, for example, is very strong. A magnet can pull on another object harder than the entire mass of the earth's gravity can. That's why you can pick up your keys with a magnet - that tiny magnet is much, much more powerful than the whole planet. The forces binding atoms together are stupendously strong.

 

[Umbran]

But yes, in short - space can "expand faster than the speed of light" because it doesn't require motion; but the words we use in conversation here can make that confusing. Physicists use equations and stuff to say it accurately, but we normal people don't talk that language and have to rely on our bad analogies and vague terms!

Physicists, feel free to chime in!

Close.

It is more accurate to think of it this way: we normally think, "take a known speed, multiply it by a time, and you get a distance". So, take the speed of light, multiply it by the age of the universe, and we have the maximum distance between two objects in the universe.

There are several flaws in this picture. The immediately relevant one is as I've said - the clocks and measuring sticks are not constants, either across the current universe, or over the history of the universe. To quote Wikipedia: "Distances obtained as the speed of light multiplied by a cosmological time interval have no direct physical significance".

 

[Umbran]

If we point a really great telescope at an object that is 45 billion LY away, that object is impossible unless something "special" has happened.

I repeat - the speed of light multiplied by a cosmological time does not get you something physically meaningful. Much as your intuition says it should, it doesn't.

Is some of the "special" that during the big bang, time went "faster" so matter could get spread out farther in less time?

Not really. There are what are called "inflationary" models, in which there's a "period" before the appearance of normal matter, normal subatomic particles, and light, where the universe can grow to great size before there are any "things" in the universe relative to which we can measure speeds. The "speed of light" has no meaning in a universe in which light does not exist. *Time* doesn't even have a whole lot of meaning in an inflationary period, as what is inflating is spacetime - so time is inflating with space.

Inflationary models are widely, but not universally, accepted.

Is all the fuzzy speak because physicists don't want to admit that stuff went faster than the speed of light when measured with an absolute stopwatch outside of the universe?

No. The English language is designed to express concepts relevant to normal human experience - distances on the order of millimeters to miles, and times on the order of seconds to lifetimes. The talk seems fuzzy because we are speaking of things not generally observed in day-to-day human experience, so your language is ill-equipped to handle them. But, you guys don't know tensor calculus, the language in which this stuff is more easily and clearly stated.

And, honestly, as we understand things today there is no such thing as an absolute stopwatch outside the universe. "Time" is a concept that is only relevant *inside* the Universe.

Is the universe actually injecting space between objects, contributing to additional expansion, separate from their natural movement as trajectories from the big bang?

It is perhaps more accurate to say that space is getting bigger between objects, but yes, close enough.

If yes, then isn't our own solar system expanding?

Morrus got this right - local conditions can overcome the expansion effect. Your local solar systems and galaxy are tightly bound. It is on scales outside that, where the universe is even more empty space than here, that the effect becomes obvious.

 

[Janx]

Close.

It is more accurate to think of it this way: we normally think, "take a known speed, multiply it by a time, and you get a distance". So, take the speed of light, multiply it by the age of the universe, and we have the maximum distance between two objects in the universe.

There are several flaws in this picture. The immediately relevant one is as I've said - the clocks and measuring sticks are not constants, either across the current universe, or over the history of the universe. To quote Wikipedia: "Distances obtained as the speed of light multiplied by a cosmological time interval have no direct physical significance".

Why not?

In your BullGrit example, BG grows, so of course he's a lousy unit of measure. My yard stick is 3 feet long. It's made of wood. It's a done deal. i teleport anywhere in the universe and start measuring, it should not change.

So, does the universe act wierd and warp the size of my measuring stick in other places in the Current universe?

 

[Morrus]

Why not?

In your BullGrit example, BG grows, so of course he's a lousy unit of measure. My yard stick is 3 feet long. It's made of wood. It's a done deal. i teleport anywhere in the universe and start measuring, it should not change.

So, does the universe act wierd and warp the size of my measuring stick in other places in the Current universe?

But things have a different length depending on how fast they're moving. And there's no absolute frame of reference or stationary point to measure it against, so your stick is always moving relative to everything else.

At the scale of a yard, of course, it's miniscule; you can't perceive it. But at the scale of billions of light years of you adding up those miniscule differences in the length of your stick it ain't!

The size and speed of your stick is always relative. To lots of different things moving in lots of different ways. There's nothing you can point at and say "that's stationary, so let's make the stick stationary relative to that".

Physicists once thought there was an ether that things moved through and that speed was relative to that ether - because that was the only way they could get their head around it. They took a long time to realise that that *everything* is measured relative to everything else, and that there's no absolute measurement.

 

[RangerWickett]

I love how Umbran says stuff like "your solar system." It makes me feel like I'm talking to an alien or a time traveler.

Dude, got any good stock tips, or perhaps instructions on how to build a hoveboard?

 

[Janx]

I repeat - the speed of light multiplied by a cosmological time does not get you something physically meaningful. Much as your intuition says it should, it doesn't.
.

Thanks for your patience in answering all these goofy questions. Here's more:

Why isn't there an absolute unit of measurement? The King declares how long a foot, a mile is, etc. Sure its arbitrary, but once chosen it. works.

Why can't we declare that 1 Umbran = the physical distance that a photon of light travels in a year as measured on Umbran's home planet.

And then start charting out stuff from that?

 

[Morrus]

Thanks for your patience in answering all these goofy questions. Here's more:

Why isn't there an absolute unit of measurement? The King declares how long a foot, a mile is, etc. Sure its arbitrary, but once chosen it. works.

Why can't we declare that 1 Umbran = the physical distance that a photon of light travels in a year as measured on Umbran's home planet.

And then start charting out stuff from that?

We already do that. One meter is defined as the length of the path travelled by light in vacuum in 1⁄299,792,458 of a second.