If the universe is expanding at an accelerated rate why don’t we feel the inertial force of the acceleration?

Question

According the Newton’s first law we should feel the inertial force of any acceleration. It is supposedly inescapable right? So where is the inertial force of the accelerated expansion of the universe? My guess is that we do experience this as gravity. If we could figure out the force of inertia created by the acceleration of the expansion of the universe would it be equal to the gravitational constant?

I’ve asked this question three different ways now and still don’t have any answers to it besides foolish ones left by children or pompous ones left by elitists who feel I need ten more years of education and a dictionary (I spell checked it this time! OK???) before I'm even allowed to ask such a question. Can anyone answer this question for real?

Seems everyone that answered has forgotten that acceleration means because they keep saying things like you don’t feel the rotation of the Earth and other such nonsense. You don’t feel the rotation of the Earth because it is not accelerating but it rotating at a steady pace. If the Earth was accelerating you would indeed feel it!
Or another foolish example posted below was that you don’t feel the speed of a car going 65 MPH either. Of course not, because the car it is not accelerating either but you sure do feel it when going from 0 MPH to 60 MPH. Come on people think!

Remember the universe is not just expanding at a steady rate but that the rate of expansion is accelerating. That means the universe is expanding fast now then it was when you started reading this.

Thank you for all the great answers so far. One theme that seems to continue is that we couldn't feel this inertia because it is so small. However, please remember that the gravitational constant is ALSO extremely small (weakest force in the universe) and it's origins are not understood as well. So it seems to me that we have two very small forces one (gravity) that we can't expalin and one (the inertia of the expansion) that we came seem to experiance. Why couldn't they be the same thing?

One more thing that just occurred to me is that many of you are answering that the universe seems to be expanding faster the farther out we look so the rate of expansion is not a constant and therefore could not be related to the gravitational constant. I would ask you to remember that we are not interested here in the rate of expansion but rather the change in that rate over time. The acceleration of the expansion could very well be the same everywhere. In other words I feel the same acceleration when going in my car from 0 to 30 as I do going from 30 to 60 but in the end I am traveling at half the speed. It just may be that the farther things were away from us the sooner they were effected by whatever is causing them to expand so they started expanding first and are therefore moving faster than we are now but accelerating at the same rate.

Answer 1

If you're going to bash people have your facts straight.
Rotation with constant angular velocity is acceleration.

Answer 2

That's a great question! I dont know, but perhaps it's because the force is too small for us to notice. For a long time the only way they've even detected the expansion is through the red shift of the spectra of distant stars. However, are the objects within the universe expanding? As I understand it, the objects are all moving away from each other, resulting in an expansion of the universe containing the objects, but the objects themselves are not expanding; they are just moving away from each other at a constant speed. For the objects (including our Earth) to change speed would require an outside force, which we would detect.

As for rotational dynamics, technically acceleration is a change in velocity. Velocity includes not just a speed but a direction too. If a direction changes but the speed is constant (such as in a rotation), that's considered acceleration. But for that to happen, a force must be applied to cause the change in velocity. If you attach a ball to a string and spin around, you are pulling on the ball causing the direction to change, preventing the ball from moving in a straight line; you are continuously applying force toward yourself. If the ball breaks free, the force will be gone and the ball will shoot outward in a straight line, no more rotation. The same is true with gravity holding us on Earth as the Earth spins and we stay on it, pulled inward towards its center without shooting off in a tangential motion (ouch!).

You're right that too many people don't understand that 65mph is a constant speed, and thus no acceleration, and you're right that we can feel acceleration. If you're inside a car and the car accelerates, you accelerate with it, and you feel it. If a plane flies at constant speed (and no turbulance) it's not possible to detect the high speed you're traveling because there's no acceleration. Einstein taught us all this and it's basic physics.

Answer 3

For one thing, Newton's first law states that an object that does not feel force will maintain uniform motion. This is clearly not the case for an accelerating universe (since the velocity of expansion is not constant)
Newton's second law states (roughly) F=ma. Which means that any mass will be accelerated by a force, or conversly if a mass is accelerated then there must be a force applied to it.
Now lets ask ourselves what exactly is expanding with acceleration?
One answer is all of the masses in the universe. According to this we should actually feel the force acting on as as the universe expands. As an example of such force imagine yourself in an elevator. When the elevator accelerates at the beginning of the ride you may feel a little bit heavier, this is exactly the force of the acceleartion.
We might think of all the planets and heavnly bodies as stuck to a fabric (the fabric of time and space). Then we might say that the masses in the universe remain in place and it is this fabric, or space itself, that is exapanding in an accelerated fashion. Since space has no mass we can dodge Newton's second law and claim that there is no force (although this is just semantics).
To tell you the truth nobody actually knows if the universe is expanding or not (or even if it is infinite or not), even Einstein himself wasn't sure of the answer. Some people believe it is expanding at constant speed, others believe it is decelerating, but the answer is still unresolved (even on Yahoo! Answers).
Your question is excellent and it shows a deep understanding of the fundemental laws of physics. To tell you the truth, the theory of relativity which deals with the expansion of the universe actually describes any and all forces as some sort of gravity, so you were even correct in your assumption! However the answer to this is not simply the gravitational constant, since the gravitational constant doesn't have the correct units to be thought of as force. To truely understand this subject you must study the theory of general relativity.

Answer 4

When the Universe is expanding, it is the whole of the universe that is expanding. Earth and other massive bodies are kept together because of gravity. The image to have is not a balloon that you are stretching from the sides but rather a bread cooking in the oven. Simply put, it isn't the "perimeter" of the Universe that is expanding, but rather every point inside the Universe getting further apart from each other. Without the force of gravity earth would keep getting stretched. So, because of gravity, Earth is exempt from being stretched, therefore feeling acceleration. Also, earth rotates at a relatively constant speed, but it's revolution isn't always at 30km/h it varies and if it varies, it means that there is acceleration. Yet we don't feel it because it is small. Which could be another hypothesis for why we don't feel the Universe's expansion.

Answer 5

First, the expansion of the universe is the expansion of space itself, so you'd be expanding right along with it. I'm not sure you'd feel that.

More importantly, at the local scale, the expansion rate is infinitesimal. The Hubble rate is currently pegged at around 70 km/s per Mpc. One Mpc (megaparsec) is 3x10^19 km. At the scale of the diameter of the Earth, this would amount to a differential of about 30 pm/s (30 x 10^-12 m/s). If this rate doubled in the next second, you'd be accelerating away from the center of the Earth at 15 x 10^-12 m/s^2. . For comparison's sake, the gravitational acceleration from a 2-ton vehicle in your driveway 10 meters away is around 1.2 x 10^-9 m/s^2.

Answer 6

In the first place, while there is some evidence that the rate of expansion is increasing (i.e., accelerating), that does not make it a fact, as you imply it is.

In the second place, even if the rate of expansion has increased, the increase is spread over fifteen billion years, which would probably make the acceleration infinitesimal, by human standards.

In the third place, it is (as was pointed out above) space that is expanding, which means that the objects within it (stars and planets, you and me) are not actually being subjected to any force that accelerates them and us. Consider this: if stars and planets are actually being accelerated as by applied force, they must be gaining mass/energy. This would be a violation of the Second Law, because the total energy of the U. would be increasing. Not saying it couldn't happen, but, you'd need to re-write physics if it is.

Answer 7

Some interesting answers here. I would just add that the expansion of the universe is apparent on large scales and you have to get out beyond the Virgo Cluster of galaxies, to which our local group of galaxies appears to be gravitationally drawn, to even try to measure the Hubble flow. Even though Einstein managed to nicely equate gravity and acceleration, the "feel" of earth's gravity must certainly far outweigh any microscopic effect the accelerated expansion of the universe has on us. There is a one-year experiment happening at this time, I believe, where two satellites were launched into high earth orbit with two of the world's most accurate gyroscopes on board to try to measure time "frame dragging," which can maybe "feel" the expansion of space as it relates to time and gravity. I'm way out of my league here.

Answer 8

Well it's a dumb question.
If you already know something about physics then your question should be self explanatory.

The first point in your question"According the Newton’s first law we should feel the inertial force of any acceleration"
OK, when do you expect to feel the inertial force? You're born in the inertial force of acceleration.
And no, "The gravity of the Earth" has little to do with the acceleration of the universe. The Earths gravity is a separate force in it's self.

Answer 9

Well you only feel the force while accelerating or decelerating. When you are moving at 65 mph in a car you don't feel any different than traveling at 30mph, but if you hit the gas hard, or brake you feel it. Same with a plane, becuase you are moving at the same rate. Since the universe has been expanding since before we were here, we never felt the acceleration.

Answer 10

Adam, I really don't know. I can speculate that since it happens on such a grand scale and includes the earth which we are already accustomed to it's rotations and revolutions that we do not feel it because it is a constant acceleration and not an undulating one which we might indeed feel.

Its kinda like in a car when you reach 50mph and keep it steady at 50mph, you no longer feel and acceleration or deceleration

Answer 11

Wow - so many opinions you'd think this was Religion!

My personal thoughts are this - you don't feel the acceleration on our scale - it is infinitesimal. I don't think it would account for gravity because it is so slow. Also, that assumption would put us smack in the middle of the universe - you would think that we would feel heavier on one side of the Earth and lighter on the other if we could feel the acceleration.

If you want some interesting thoughts about gravity, check out The Final Theory (www.thefinaltheory.com). I personally disagree with a large portion of this work, but hey - to each their own...