What is Space?

It gets weirder than that. A lot weirder. If you haven't done so already, check out the Unruh effect. Observers who are accelerating may find themselves in different, decoupled reference frames. An accelerating observer perceives black-body radiation where a non-accelerating observer does not. "Hence, the observers will see different quantum states and thus different vacua."

-e

Remarkable, thanks for the heads up e.

I think I'll have to read about the Unruh effect about 50 more times to begin to get it, but roughly the idea is that an accelerating mass experiences a background radiation from space equivalent to a blackbody temperature of

T= ha/4π²ck_B

where a is the acceleration, h is planks constant, c is the speed of light, and k_B is the Boltzmann constant.

So for extremely large accelerations, space is a boiling cauldron, yikes.

A boiling cauldron of virtual particles either going in and out of existence or coming into existence, but missing when they try to go back together.

So basically, while accelerating, one creates their own event horizon that interferes with the virtual pair process - separating them and causing Hawking Radiation!

Woof!!!

Which poses an interesting question: it's pretty much a given that the speed of light is a universal upper bound on velocity, but might there also be an upper bound on acceleration? Perhaps a maximum delta-vee in the distance of one Planck Length? Perhaps? And what would the universe be like for one so accelerating? I'd say apart from the enormous forces involved, the observer would be instantly fried to a crisp.

-e

Hi -e, you said: "... but might there also be an upper bound on acceleration? Perhaps a maximum delta-vee in the distance of one Planck Length? Perhaps?"

I would rather say "... a maximum delta-vee in one Planck Time?"

AFAIK, relativists think there's no theoretical upper limit for acceleration, but surely there must be a practical limit! I can think of the deceleration of a relativistic particle colliding head-on with a much heavier particle as (perhaps) a sort of upper limit.

To be "fried to a crisp", one don't need heavy acceleration - just keep up 1g in free space for a few years. The background will become white-hot up front...

Regards, Jorrie

Either way, it certainly explains why Nolan Ryan's pitches arrived smoking!

-e

Indeed!

BTW, maybe we can quantify the upper limit for "smoking" acceleration:

ΔV = c and ΔT = T_Planck, so

a_max ~ 10⁸/10^-43 = 10⁵¹ m s^-2.

Wow!

Jorrie

Yes, Wow!

-e

Since acceleration is exactly like gravity in the proper inertial frame of reference, my guess would be you'd become your own black hole.

Hi vermin, you said "Since acceleration is exactly like gravity in the proper inertial frame of reference, my guess would be you'd become your own black hole."

With near infinite acceleration, I agree - too much energy in too small a volume...

With moderate acceleration, there may still be event horizons, but no black holes - although to the front it should look like a white hole and to the rear like a black hole...

Jorrie

I understand the white hole, but why a black hole in the aft direction?

Hi vermin, you asked: "but why a black hole in the aft direction?"

With even moderate constant forward acceleration, there is a distance behind you from where no photon can every reach you. This is a pseudo event horizon, in appearance similar to a black hole's horizon. The distance to the horizon is r = c²/a in SI units.

Regards, Jorrie

I'm confused. I thought one of light's properties (according to Einstein) is that if you move away from a source of light, no matter how fast, you still see the light coming at you at c?

Hi vermin, the constant (measured) speed of light will be strictly true only for a momentarily co-moving inertial frame, not for the accelerating frame. All bets on a constant c are off in the direction of the acceleration.

In the case in hand, the photon never reaches you, so there is no speed to measure. Another way to look at it is that the Doppler factor of a photon coming from just within the event horizon range will tend to infinity...

Jorrie

I will accept that the light behind you would Doppler shift (possibly approaching something like infinity {maybe...}), but I'll bet it would still catch up with you. Though you may not know it, unless, of course, you were carrying aluminium foil in your pockets. In which case, your pants would start to spark and catch on fire.

On the other hand, did Einstein ever consider wardrobe when doing his thought experiments? Hmmmmmmmmmmm... "Boxers! No briefs!"

I was in the elevator with one of our astronomy professors here and asked her, in all (feigned) seriousness, "If a black hole produces lots of gravity, does a white hole produce lots of levity?"

-e

If I had a horse, I'd horse-whip you!

So, Europium, both pair creation and Hawking Radiation seem to play an ever increasing part in space-time! Possibly DE or DM?

Hi masu, shows you, there is no definitive definition (whatever that may mean, a-la Stephen Hawking), of Space!

Regards, Jorrie

This is what space is:

Planets
Galaxies
Solar Systems
Meteors
Comets
Black Holes
Quasars
Astroids
Stars
Moons
Nebulas
Star clusters
and that about wraps it up.

I hope we finaly got it.

No, that's

Matter
Matter
Matter
Matter
Matter
Matter
Matter
Matter
Matter
Matter
Matter
and, of course,
Matter

We've come close to a definition for the fundamental stuff of space (or space-time), but your list is not it. First one to provide a decent answer, wins ten acres on Mars guaranteed to be the landing spot! Be the first one on Mars to yell "Hey! You kids! Get off my lawn!!!"

Location, location, location!!!

Space is made from levity. It's gotta be, cuz gravity pulls things together. But space is expanding, faster and faster, and so it can't be gravity from all that matter stuff you mentioned. You know, things like planets, and thingies going 'round other thingies, and them going 'round even more and bigger thingies and not even in decent circles half the time, what with all that wiggling goin' on from peterbations an' stuff. And all that matter means one thing: gravity. And, as everyone knows, gravity sucks. Because the Universe is expanding like some balloon being blown up by some friggin' spaced-out speed freak at Rush Hour, it must levity, cuz levity really blows. And you didn't even mention gas and dust and dark stuff and all that other crap between all that stuff you mentioned. That in-between stuff counts too, 'specially cuz it's the in-betweenness that counts as space. All that other stuff you mentioned is just space clutter. Some people can't see the galaxy for the planets.

That pretty much wraps it up, I think.

-e

So far, you're first in line for that 3 bdrm, 2 bth on the red planet! Just watch out for those sub-par loans... What am I thinking, it'll take at least a trillion dollars just to evict you!

Can I put my junk cars up on blocks in the front yard just like back home? And an old washing machine and my favorite sprung couch on the porch? This place does have a porch, don't it?

-e

The real estate agent is looking into it now...

Not that guy! He's the one who sold me that Florida swampland.

-e

What? To him it was a good investment!!!

Besides, the very first day of medical school and the very first words out of your instructor's mouth are "Invest in real estate."

I shouldn't complain, really. That 'gator shore is good eatin'!

-e

and crawdads!!!

Did you get my email reply?

I did, but you evidently did not get mine. I sent a second message, but I've had trouble with CR4's emailer before. Revisit your mailbox in a few hours and see if anything from me came through. If not I'll have to try again.

-e

If space doesn't exist, then how can it be affected.

Just peeking in through the looking glass.

There are places we know , and there are places we know we don't know .There are places that we don't know that we know ,and there are places that we know that we don't know that we know.These places are space.

well,kinda.

All of them? Just kidding!

-e

Ok, let me see if I've got this right....accellerating objects encounter black body radiation.Does it work the same with deceleration. If a long rod is accellerated, the molecules in the back end must move faster to keep up with the front?Even if the accelleration force is uniform along the entire length, the molecules in the back end encounter a slight "negative G force?What about a circular, rotating object with the angular velocity increasing , while at the same time being accelerated linearly?

Would the "negative G force" be in direction exactly opposite of the linear accelleration, or would there be "frame dragging?"Now picture a gymbal mount, such as a gyroscope is mounted on, and accellerate in both angular directions, as well a linearly.Where are the forces acting now?

Ow! Ow! My head! OW!!

Hi AstroNut, here at my UT+2, it is really time (~21:00) to work on the headache of tomorrow morning, so I feel with you!

Regards, Jorrie

Ow! Ow! My asteroids! OW!!

It's my guess that acceleration or deceleration makes no difference. One of the first things taught to us in calculus was "Zer iz no deceleration! Only acceleration!"

As for angular momentum, one side of the spinning object (in the direction of motion) would be in a slightly different reference frame than the other. Though not by much. As for frame dragging, you'd have to be really really heavy for that to happen. Perhaps if you were moving at 99.999999999999999...% of c.

But this is just a guess.

Space is a distance between two points of reference, with all matter and energy between and around these points removed.This type of space can only exist hypothetically.In reality, spacetime is an ocean of energy, permeating "over, under, around and thru" (to paraphrase an old cigarette commercial) all matter within it.It takes a longer (curved) path when it encounters matter, because it must "navigate" thru the minutest openings of the matter.This causes it to appear to "deform" and time to "slow down" around matter.The denser the object, the more difficult the path, and the more curvature of spacetime.

Oversimplified, I know, but it fits for general purposes. Just wanted my hat in the ring for that Mars land rush.

I would like to set up a candy factory on Mars, but the best name is already copyrighted. Perhaps the "Earth Candy Company" would work?

Here is another shot in the dark about space.

It is the property of our universe that allows and controls motion.Is space the child of motion? When the "big bang" exploded,the internal pressure of the singularity exceeded the structural integrity of the singularity and space,time, energy, and matter that had been previously infinitely compressed sprang forth.Space,time and motion are intertwined from birth, as is matter and energy. The energy is still expanding, like a bottle of carbonated water when you release the cap.This causes space to expand likewise.

Hey! Who turned out the lights....

This is purely Hindu philosophy. That the fundamental event for all conscious beings is a thought. The first (or the basic) thought of all beings is the 'I- thought'. This I-thought is also called Ignorance/Maya/ Moola-Maya, etc. It cannot be comprehended, but its properties can be 'seen' mixed up in everything. The distance between two events gives rise to the concept of TIME. Time also signifies 'change'. It is this element of time that projects the concept of SPACE as well. So, using the language of modern Physics, one can say that TIME/SPACE quantum is the projection of the thought that follows the 'I thought'. That is why, in English, the fundamental unit of time is 'second'. It is only after time/space has happened that the world of plurality can be observed. So, going back, the Supreme Consciousness (Para-Shiva, Brahman, Yahveh, or whatever name people use) having become conscious ofitself (through Moola-Maya, Itchha Shakti, or whatever name one uses, personified as Parvati Devi), sets forth 'creation'.

Ok all nonsense and joking aside space the final frontier where no man has been before. It is simply the absence of matter.

And energy, for E=MC2.

But on really, really small levels it seems that "empty space" and mass and energy sort of foam in a broiling mixture of virtual particles and areas of non-existence. So it does have the properties of some sort of stuff.