At what speed does an object become, in effect, invisible to the naked human eye?

Question

Also, at what speed does an object become blurred or distorted to the naked human eye?

Impossible? Speed of light?
I'm not so sure...
What about a bullet from a gun? The naked eye can't see that... I'm fairly sure that bullet isn't moving at the speed of light.
Or I've seen footage of animals that pounce on their prey so fast the human eye can't see it. I doubt they're moving at the speed of light as well.

"Depends on the size of the object and it's distance"

Okay, then assume it's got about the same mass as an average adult and it's within your general area.

Answer 1

There is NO SPEED at which an object would become, in effect, invisible to the naked human eye, SOLELY due to moving at extremely high speed, since both DISTANCE, your ability to SWIVEL your head and follow it with your eyes, and the direction of travel are also involved as factors. In other words, it would be due to a COMBINATION of factors, of which speed would be an important one, but not the only one.

(For example, if a cruise missile flew by you from right to left within a few feet of your nose at 600mph, you probably wouldn't see it. But have it do so at a range of two or three miles and you COULD follow it with your eyes, seeing its outline and fins quite clearly. (Such views over Baghdad appeared many times on CNN at the start of the first Gulf War.)

If we talk about relativistic, truly near-light speed, the object would still not necessarily look blurred, depending again on the direction it was traveling in. (But more of this later!)

It would however appear distorted, though not in the way that was written about for over fifty years. Rapidly moving objects do NOT appear "squashed" by the Lorentz contraction, as everyone, including George Gamow in his wonderful Mr Tomkins books (incorrectly) assumed.

In the late 1950's, Roger Penrose first showed that a FINITE sized sphere would remain looking EXACTLY like a sphere (i.e. appear to have a perfectly circular outline), no matter at what speed and from what angle you were looking at it! However, there's more:

Not long afterwards, James Terrell proved something more detailed that really blew physicists' minds. He showed that sufficently SMALL, relativistically moving objects DON'T appear SQUASHED, they appear ROTATED! For example, it turns out that the Lorentz contraction of the side facing you is indeed seen, but at the same time you see a part of the object that is "trailing" in the motion, that you wouldn't see if it were stationary at the same position. (This happens because of the ballistic nature of what happens to photons leaving the normally unseen trailing side; it's a so-called "aberrational" effect.) The net result is that the Lorentz-contracted parts plus the now seen trailing parts combine to look like a simple, straightforward rotation in a stationary Newtonian case. Quite mind-blowing!

I said above that this was for SMALL objects. The reason is that this "aberrational effect" depends on three things: the speed, the direction of travel, and the angle from which you're looking at it. As any one of those changes, the "apparent rotation" seen for a given small object changes. If you now consider a larger, finite sized object, that means that it will seem to have a VARIABLE angle of apparent rotation at different points as you scan your eye across it. That means that the thing might look "rotated" in the large, but it will appear to be a sort of "bendy" rotation!

What that means for Penrose's sphere is that if you had drawn the outline of countries and continents on it, as on a terrestrial globe, the OUTLINE of the whole rapidly moving sphere would still look like a sphere, but the different parts of the seen surface will have been rotated by variable amounts, and so the outlines of countries and continents will appear distorted from their terrestrial originals.

Finally, there are other problems with something heading directly away from you or towards you. If going away from you, the photons you'd receive could be red-shifted to such low frequencies that your eyes couldn't register them. On the other hand, if the object were heading towards you, the photons from it could be so blue-shifted that they'd become in turn ultra-violet, then X-rays and then gamma rays as the speed was continually increased, so that they'd burn out your eyeballs. (All these effects could happen to a greater or lesser degree when the rapidly moving object was viewed from within certain velocity-dependent angles of its direction of motion.)

Relativistically, it's a bizarre optical world out there!

Live long and prosper.

Answer 2

Human Eye Speed

Answer 3

it depends on the distance from you ,speed and size lets say you looking at a comet its not blured but its moving very fast but it you was only 30 feet from it when it pasted the comet would be a blur because it was so big but if it were small like a bullet it would be invisible I'm not sure what the limit that the human brain can perceive images but there got to be a limit im think a type of frame per second limit if the bullet can get threw your fram of sight before your brain can pic it up im sure it leaves it out ,just my thoughts i might be wrong

Answer 4

Depends on the size of the object and it's distance. If it's the size of a city and 2 miles away, even going 300,000 mph, it would not be blurry.

Or like Gene said, if it's the size of a large star and 30 trillion miles away, I can watch it go probably near the speed of light.

Answer 5

At the size of an adult human male light speed will do.

Theoretical experiment:
An Adult male human (capable of travelling the speed of light) stands one metre away from you, (his back facing you) he starts running at the speed of light. By the time the light gets to you of him starting to move he is a metre away by the time he is 4m away he appears to be 2m away by the time he appears to be 4m away he will be 8m away so on and so forth. He's not really invisble its just when you see where he is he isn't there any more (this would all happen to fast for you to focus on anyway).

However assume E=MC² then his mass will be such that the entire universe will collapse as soon as he starts moving.

Also I thought you might like to know that humans need to be able to focus on an object to see it if its not in the one place for long enough we can't focus. SO this all comes down to reaction time so the worlds fastest reaction time is 0.00001 seconds (by a human) to jerk his finger (the standard colour test, when this changes colour jerk your finger). Yes this test was repeated to confirm results

Answer 6

it has to do more with the refresh rate of your eyes and the angular velocity of the object in reference to your eyes. the human eye can detect a flicker at around 60 Hz, that means the human eye can detect something moving in front of it in as little as 16 milliseconds. so if an object crosses your field of vision in less than 16 millisecondsyou probably wont see it. Now why does angular velocity have anything to do with it? because angular velocity is related to the distance from your eyes. if something is 1ft away from your eyes, you have about a 3 foot field of vision, and the object only needs to cover 3 feet in 16 milliseconds. thats about 275 MPH. if the object is 100 miles away though, the object has to travel a few hundred miles in that same 16milliseconds. thats why you can see shooting stars and things in space travelling at thousands of miles an hour, but you cannot see a bullet.

Answer 7

some refenence to "in effect invisible" to naked eye could be traced when an observer finds the imaginary traveller heading headlong under the onslaught of strong gravitational pull into the black hole having become stationary - or in effect invisible - after reaching the CHandrashekhar radii limit vis-a-vis that black hole. Because the escape velocity for such contracting black hole has exceeded "c" and even light can not escape onto observer - from that distance limit.

I do not know how else this can be conjured.

Answer 8

There are a lot of factors to consider. I think your eye can't resolve anything it sees for less than like a tenth or a twentieth of a second. That's why we don't perceive any flicker when watching movies.

Ultimately, a lot of what you think you see, you really don't. Your eyes only really register a few broad things and your brain fills in the details.

Answer 9

i think the object would have to be perfectly still along with your eyes, so its impossible. i dont think you could do an accurate test on it because your eyes would automaticly follow the object at diffrent speeds. things start to go blured when your eyes cant keep up with something so it loses focus

Answer 10

i would think that it would be just a little faster than the speed of light, therefore the object is travelling faster than light, light cant catch up to it, or even reflect off of it - and if light isnot reflecting off of it, then the image cannot bounce back to our eye to be seen.