# How fast does a human sized object need to move so I won’t see it?

• gen66
In summary, the conversation discusses the question of how fast an object needs to move in order to be undetectable by the human eye. The conversation includes mentions of the Flash, the speed of sound, and human perception limits. The conversation also touches on the role of biology in determining what a human can see. Ultimately, the question is left unanswered due to a lack of specificity and potential trolling.

#### gen66

Summary:: How fast does a human sized object(or a human) need move so I won’t be able to see it at all if it passes right next to me?

Im trying to figure out something in regards to the Flash movies/Flash series but I’m super bad at calculations and math :(
Do you think that mach 2 speed(2469km per hour) is enough for me to not see at all a human sized object passing right next to me?

Dale
The Flash travels at the speed of plot, I'm afraid. He, along with many fictional characters, exists in a universe that does not have a coherent physical law because the writers don't have a coherent physical model in mind when writing.

russ_watters
I thought the question was about the Flash video format.

Barry Z, BillTre and russ_watters
gen66 said:
Do you think that mach 2 speed(2469km per hour) is enough for me to not see at all a human sized object passing right next to me?
What about the supersonic shock wave? That might get your attention. As previously mentioned, fantasy is fantasy.

hmmm27, BillTre and pinball1970
gen66 said:
Do you think that mach 2 speed(2469km per hour) is enough for me to not see at all a human sized object passing right next to me?
That should work, since you will be knocked unconscious by the shock wave, so you won't be seeing anything until you (hopefully) wake up in the ICU...

BillTre, pinball1970, phinds and 2 others
beat you...

pinball1970 and berkeman
Ah, still no serious answer :( Ok, please ignore the shockwave the object will create and let's focus only on visibility, how fast it would need to move to be undetectable by humans eyes, e.g. distance 1 to 10 meters away from the eyes.

gen66 said:
Do you think that mach 2 speed(2469km per hour) is enough for me to not see at all a human sized object passing right next to me?
Depends the viewing angle, light conditions, and your concentration. I sometimes don't notice people passing me at normal walking speeds.

pinball1970
A.T. said:
Depends the viewing angle, light conditions, and your concentration. I sometimes don't notice people passing me at normal walking speeds.
If I give you all these, would you try to answer the question or you would just ask for more specific details and variables?
Just a normal viewing angle right in front of you, at eye height or a little bit lower. Light is bright day at 13pm, no clouds. Concentration level is medium, you're just gazing in front of you, it's enough concentration to see an incoming fly/insect in proximity.

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gen66 said:
Just a normal viewing angle right in front of you, ...
The key is: Are you looking exactly perpendicular to the object's path, or at some oblique angle? That affects how long the object stays in your field of view, and its angular speed across your field of view. This is more a biology question about human perception limits, rather than about physics.

gen66 said:
Ah, still no serious answer :( Ok, please ignore the shockwave the object will create and let's focus only on visibility, how fast it would need to move to be undetectable by humans eyes, e.g. distance 1 to 10 meters away from the eyes.
You may see it but your brain would probably be unable to process the data.
Subliminal cuts in movies are in front of your eyes for a fraction of a second but tend not to notice them.

A.T. said:
The key is: Are you looking exactly perpendicular to the object's path, or at some oblique angle? That affects how long the object stays in your field of view, and its angular speed across your field of view. This is more a biology question about human perception limits, rather than about physics.
It's perpendicular, question is about physics, it's definitely not a biology question. I'm asking about speed, the answer contains speed, where is the biology in speed? No matter what information you get, you just won't answer the question. Just say it's a difficult one and you don't know and that's it.

berkeman and BillTre
pinball1970 said:
You may see it but your brain would probably be unable to process the data.
Subliminal cuts in movies are in front of your eyes for a fraction of a second but tend not to notice them.
thank you for the answer. It doesn't contain any numbers unfortunately. Question was about the necessary speed needed.

47

pinball1970 and russ_watters
hutchphd said:
47
aha, if there were less trolls around these forums It would be amazing :)

This answer has the same level of specificity as the question. You asked for a meaningless number, and I gave you one.

BillTre and berkeman
gen66 said:
it's definitely not a biology question.
You are asking what a human can see. This is determined by human biology.

pinball1970 and BillTre
gen66 said:
aha, if there were less trolls around these forums It would be amazing :)
There's an old saying, "It takes one to know one."

Bystander and hutchphd

## 1. How is the speed of light related to the human eye's ability to see objects?

The speed of light, which is approximately 299,792,458 meters per second, is the fastest speed at which an object can travel in a vacuum. This means that any object moving at or faster than the speed of light would be invisible to the human eye, as our eyes are not able to process visual information at such high speeds.

## 2. Is there a specific speed at which an object becomes invisible to the human eye?

No, there is no specific speed at which an object becomes invisible to the human eye. The speed at which an object needs to move in order to become invisible to the human eye depends on various factors such as the distance between the object and the observer, the lighting conditions, and the sensitivity of the observer's eyes.

## 3. Can a human sized object ever reach the speed of light?

According to the theory of relativity, it is impossible for any object with mass to reach the speed of light. As an object approaches the speed of light, its mass increases exponentially, making it require an infinite amount of energy to reach the speed of light. Therefore, a human sized object cannot reach the speed of light.

## 4. Is it possible for an object to move so fast that it becomes invisible to the human eye?

Yes, it is possible for an object to move so fast that it becomes invisible to the human eye. This is known as the "blur effect" and can be observed when objects are moving at high speeds, such as a speeding bullet or a race car. However, this effect is only temporary and the object would become visible again once it slows down.

## 5. Can technology help us see objects moving at speeds faster than the human eye can perceive?

Yes, technology can help us see objects moving at speeds faster than the human eye can perceive. High-speed cameras and advanced imaging techniques can capture and slow down the movement of fast-moving objects, allowing us to see them in detail. However, even with technology, there is a limit to how fast an object can move before it becomes invisible to our eyes.