Reply to: The size of the universe

[scooterscot]

As it happens I was an electronic engineer working on radar many years ago, and we did know about interference patterns apparently travelling faster than light.

The lecture we got was, don't, but sir what if... don'T ask! Don't ask ever! Even since I've done nothing but ask questions.

[Doggy Styles]

Apparently. But if you ever get involved with RADAR, waveguides etc you'll be told how the pattern of the energy in the waveguide is set up prior to the transmission. As the pattern covers more distance than the path of the energy the pattern must be established faster than the speed of light. A physical impossibility since the speed of light is fixed.

But this is where it gets interesting. A pattern is not physical, has no mass. For me by definition light must has some mass otherwise why would the speed of light be limited?

As it happens I was an electronic engineer working on radar many years ago, and we did know about interference patterns apparently travelling faster than light.

[scooterscot]

Depends on the speed of dark matter. They'll let you know what speed that is when they eventually catch some.

Who's your money on, the Road Runner or Wile E. Coyote?

Well it dint work out to well for Wile E. Coyote so my money is on the Road Runner. Beep beep.

[PAH]

And what of the effects of gravity from such an event? Would they be felt on earth sooner or later or at the same time come our impending doom?

Depends on the speed of dark matter. They'll let you know what speed that is when they eventually catch some.

Who's your money on, the Road Runner or Wile E. Coyote?

[OwlHoot]

No it's not, by the very definition of theoretical physics.

If I fire a photon in one direction and ride another in the opposite direction, I see the first recede at c. Maybe. Certainly not more than c

Yes, that applies to things moving within space; but it doesn't apply to flows of space itself, such as cosmic inflation at the Big Bang or the other things I mentioned.

edit: Quoting from that Wikipedia article on Inflation:

While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such constraint in general relativity. An expanding universe generally has a cosmological horizon, and like a black hole event horizon, this marks the boundary to the part of the universe that an observer can see. The horizon is the boundary beyond which objects are moving away too fast to be visible from Earth.

[scooterscot]

There's no contradiction. You don't notice an event until the light from that event reaches you. Just like a the sun could blow up now, and we wouldn't know about it for another eight minutes.

And what of the effects of gravity from such an event? Would they be felt on earth sooner or later or at the same time come our impending doom?

[doodab]

No it's not, by the very definition of theoretical physics.

If I fire a photon in one direction and ride another in the opposite direction, I see the first recede at c. Maybe. Certainly not more than c

But if the space between expands fast enough you don't see anything.

[scooterscot]

Space pours into a black hole faster than light speed for a distant outside observer.

Oh and everything beyond our cosmic horizon, 45 billion light years away from us in any direction, is receding faster than light speed.

Is space a fluid? Is it not the shape of space has become so warped the simplest path for light to follow is the one requiring the least energy, i.e. downwards and inwards?

The horizon of the visible universe is food for thought. Exactly how big is reality? Given the number of circumstances that need occur to allow a sentient being, such as ourselves, to ask that question is mind boggling enough. Our solar system with jupiter the giant vacuum cleaner protecting our planet from major asteroids, surviving the dinosaurs, the odds against us are staggering yet here we are.

[scooterscot]

Isn't the speed of light constant regardless of the speed of the source away from us?

Apparently. But if you ever get involved with RADAR, waveguides etc you'll be told how the pattern of the energy in the waveguide is set up prior to the transmission. As the pattern covers more distance than the path of the energy the pattern must be established faster than the speed of light. A physical impossibility since the speed of light is fixed.

But this is where it gets interesting. A pattern is not physical, has no mass. For me by definition light must has some mass otherwise why would the speed of light be limited?

[scooterscot]

I don't think there are.

Wd000hgS. Although I remember reading a new scientist article talking about faster than light galaxies.

[scooterscot]

Reality is a perception from limited senses, we're only human after all. Mathematics is a construct to try to make sense of those senses.

One example of where things get weird: There are parts of the universe moving at faster than the speed of light.

Maybe that's why they're invisible, or dark.

There invisible because the expiation of the universe is accelerating.

Reality is, I hope, not the matrix! Say, is there anyway we can prove we're all not living in The Matrix V6?

If I'm not here tomorrow you'll know the answer. An agent has me hooked with a tasty rate.

[d000hg]

Oh and everything beyond our cosmic horizon, 45 billion light years away from us in any direction, is receding faster than light speed.

No it's not, by the very definition of theoretical physics.

If I fire a photon in one direction and ride another in the opposite direction, I see the first recede at c. Maybe. Certainly not more than c

[Paddy]

Isn't the speed of light constant regardless of the speed of the source away from us?

Or is that another fine theory debunked?

Time or light is constant, and it is not time!

In 1971, experimenters from the U.S. Naval Observatory undertook an experiment to test time dilation . They made airline flights around the world in both directions, each circuit taking about three days. They carried with them four cesium beam atomic clocks. When they returned and compared their clocks with the clock of the Observatory in Washington, D.C., they had gained about 0.15 microseconds compared to the ground based clock.
Eastward Journey Westward Journey
Predicted -40 +/- 23 ns + 275 +/- 21 ns
Measured -59 +/- 10 ns + 273 +/- 7 ns

[NotAllThere]

There's no contradiction. You don't notice an event until the light from that event reaches you. Just like a the sun could blow up now, and we wouldn't know about it for another eight minutes.

[TimberWolf]

According to some theories there are parts of the universe which are beyond our horizon, as they moved away from us so fast, the light from them hasn't got here yet.

And the size of the unobservable universe is supposedly way, way, way larger than the minuscule observable part shown by the OPs link. And objects on the edge of the observable universe are blinking out of our reach forever, all the time. Under the standard model and an inflationary universe this is put down to space stretching, without a violation of the speed of light being necessary, though most of the universe isn't understood.