If you could travel at the speed of light...

[SC Maintenance]

There is a distance that objects are moving away from us as we are moving away from them, so that the total combined speed is > the speed of light.

I am pretty sure that the theory of relativity states nothing can move faster than the speed of light, including two objects moving away from each other at the speed of light. Don't ask me - apparently 1+1 = 1 at the speed of light.

What? Where do you guys get this stuff?

Quantum mechanics and the theory of relativity conflict with each other - something about time. To reconcile this some have suggested time - does not exist - or more precisely, is not what we perceive it to be.

And it could all just be made up since it's impossible to actually know

I am kind of in this camp, mainly because my puny brain can't process any of this.

So no, dark matter is not directly observed, but its effects are

There are plenty of competing theories to what causes those affects, and those differing from the dark matter theory is growing. The concept of "dark matter" was really just a made up thing to explain what was observed. All current theories could be wrong possibly.

 

[ripcord]

Dark matter was theorized to explain the lack of mass in the universe given observed gravitational effects.

 

[JeffKeryk]

"So far, the only life we know of is right here on our planet Earth. But we’re looking...we don't really have a universally accepted definition of life itself."

Biologists would disagree. Life is defined as multicellular objects or organisms exchanging mass, either in the form of solids or gases—and all life has this informational program directing its functions by its genetics, its DNA.

To say we don't have a universally accepted definition of life is to say we cannot identify life as we know it. We have to have a baseline definition as to what we observe and define as, life.

So the statement that we don't have a universally accepted definition of life is totally ridiculous. This is tantamount to saying that if we observe another highly luminous object in the far reaches of the cosmos, we don't have a universal definition of a "star."

Disagree. And apparantly so does NASA at least in this article.

From the article I cited:

Fast facts: Are we alone in the universe?​

So far, the only life we know of is right here on our planet Earth. But we’re looking.

The big question – Is there life beyond Earth? – comes with an ironic asterisk: we don't really have a universally accepted definition of life itself. That said, we might not need one. We need only detect the telltale signs of life in an exoplanet atmosphere, and we have a better understanding of what those look like here on Earth.

Here's a Biotech article.

From Princeton.

A problem arises, as I see it, is how do we know if we have encountered extraterrestrial life if we cannot define it?

Settled science?
"Any physical theory is always provisional. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory."

Prof. Stephen Hawking, A Brief History of Time

 

[MolaKule]

I would go so far as to say that we might even consider self-replicating, energy-consuming pre-cellular molecules “life.”

I wouldn't because these have been nothing other than conceptual, wishful thinking. None of these have been produced or observed in the laboratory.

The major problem is that informational molecules of DNA are needed to control cellular functions before a cell can properly function. No viable explanation has been made as to the source of these informational molecules.

 

[MolaKule]

The big question – Is there life beyond Earth? – comes with an ironic asterisk: we don't really have a universally accepted definition of life itself. That said, we might not need one. We need only detect the telltale signs of life in an exoplanet atmosphere, and we have a better understanding of what those look like here on Earth.

This is the worst case of circular reasoning I have seen in a while.

It is saying: "We don't have a real definition of life, but if we detect telltale signs of life in an exoplanet, then we can (further?) define life on earth."

The problem here is the phrase "universally accepted definition of life," as if there were some other extant life forms. What would those "other" life forms be in terms of structure and component chemistry? No one knows.

The point I am making is this: We only know what life looks like on earth and that has to be our basis for comparison for any definition of life forms.

 

[JimPghPA]

I am pretty sure that the theory of relativity states nothing can move faster than the speed of light, including two objects moving away from each other at the speed of light. Don't ask me - apparently 1+1 = 1 at the speed of light.

Quantum mechanics and the theory of relativity conflict with each other - something about time. To reconcile this some have suggested time - does not exist - or more precisely, is not what we perceive it to be.

I am kind of in this camp, mainly because my puny brain can't process any of this.

There are plenty of competing theories to what causes those affects, and those differing from the dark matter theory is growing. The concept of "dark matter" was really just a made up thing to explain what was observed. All current theories could be wrong possibly.

Maybe I'm wrong, but my understanding from what I heard is that there is a finite distance that beyond it we can never see any thing even if we had equiptment powerful enough to make it out. I assumed ( maybe incorrectly ) that was because space itself is expanding at a rate that for a big enough distance away light leaving something will never reach us.

So, its a little more complicated than my previous simple explanation.

The sum of the distance is expanding enough that light can't traverse it.

Theres also the beliefes that expansion will ( if the earth were to last long enough ) result in all stars becoming too far for their light to reach us.

Not really a concern for many reasons.

 

[Exhaustgases]

If I could travel light speed, then of course I'd want to go much faster. You know star trek speeds.

Light speed is likely very slow for other entity's.

 

[wemay]

I'm not authorized to think about things like this. But I do watch Dr. Who sometimes.

I watch it too, but all the time.

 

[goingplacesanddoingstuff]

I wouldn't because these have been nothing other than conceptual, wishful thinking. None of these have been produced or observed in the laboratory.

We have indeed produced self-replicating molecules in laboratory settings.

https://www.sciencealert.com/chemists-have-recreated-a-critical-moment-in-the-creation-of-life
https://chemistry.uchicago.edu/news/molecular-architect-rna-amino-acids-and-self-assembling-ribozyme
https://pubs.acs.org/doi/10.1021/jacs.9b10796
https://cordis.europa.eu/article/id...ules-provide-clues-to-how-life-may-have-begun
https://newatlas.com/biology/self-replicating-protocells-life-missing-link/

Any self-replicating molecule which we would observe in any system outside of earth could be considered life because it would be subject to all of the same physical laws governing all other life.

The major problem is that informational molecules of DNA are needed to control cellular functions before a cell can properly function. No viable explanation has been made as to the source of these informational molecules.

I’m not sure how this relates to the hypothetical scenario we’re taking about. Are you are saying that it is categorically impossible for anything simpler than a cell to exist anywhere in the universe? If so, I suspect an impasse and we should drop this.

 

[BigCahuna]

I think the question on everybody's lips is, if your traveling along at the speed of light, and you turned your headlights on, would you notice any difference?.,,

 

[Astro14]

I think the question on everybody's lips is, if your traveling along at the speed of light, and you turned your headlights on, would you notice any difference?.,,

That’s a question that has already been answered - and that answer is this - because of time dilation, you turn them on, and they appear to work normally, to you.

Otherwise - I wouldn’t go taking physics questions from Steven Wright’s comedy.

 

[Astro14]

Dark matter was theorized to explain the lack of mass in the universe given observed gravitational effects.

Exactly - I believe I said that.

 

[SC Maintenance]

If I could travel light speed, then of course I'd want to go much faster. You know star trek speeds.

Light speed is likely very slow for other entity's.

Photons travelling at the speed of light don't register time. ie time "stops" at the speed of light.

So if you were able to travel at the speed of light possibly the travel time would be instant from your perspective? I know they theorize time continues for you - but I can't seem to square the circle on that one.

Which brings up another confusion. Were supposedly seeing galaxies a billion light years away so apparently thats what they looked like a billion years ago. But if the photons don't register time perhaps were watching it in real time?

 

[spasm3]

Which brings up another confusion. Were supposedly seeing galaxies a billion light years away so apparently thats what they looked like a billion years ago. But if the photons don't register time perhaps were watching it in real time?

The photons themselves may not register time. But they take time to get here. So you are seeing the galaxy as it was when the photons left it.

If it's a million light years away, you see how it appeared a million years ago.

 

[SC Maintenance]

The photons themselves may not register time. But they take time to get here. So you are seeing the galaxy as it was when the photons left it.

If it's a million light years away, you see how it appeared a million years ago.

So they say. From the photons perspective it just happened.

 

[RedSpider]

The photons dont experience time, but the non-moving observer does. If you were able to hop in a space ship and get to the speed of light and get to Andromeda a million years from now, other than the time it took to accelerate to light speed, your trip would be instantaneous, from your perspective. But when you got to Andromeda and phoned home to tell your wife how cool Andromeda is, the person taking your call would inform you that your wife died a million years ago, and the only person available to take your call would be Keith Richards and he's out back having a drink and a cigarette and you need to call back later.

 

[KrisZ]

The photons dont experience time, but the non-moving observer does. If you were able to hop in a space ship and get to the speed of light and get to Andromeda a million years from now, other than the time it took to accelerate to light speed, your trip would be instantaneous, from your perspective. But when you got to Andromeda and phoned home to tell your wife how cool Andromeda is, the person taking your call would inform you that your wife died a million years ago, and the only person available to take your call would be Keith Richards and he's out back having a drink and a cigarette and you need to call back later.

We don't really know what would happen because photons aren't the same as physical particles. But I highly doubt your physical body would seize it's function during the travel time. The traveler would likely die along the way, same as his wife on earth, just never perceive the trip. It would likely be like going to sleep and never waking up.

 

[kschachn]

The photons dont experience time, but the non-moving observer does. If you were able to hop in a space ship and get to the speed of light and get to Andromeda a million years from now, other than the time it took to accelerate to light speed, your trip would be instantaneous, from your perspective. But when you got to Andromeda and phoned home to tell your wife how cool Andromeda is, the person taking your call would inform you that your wife died a million years ago, and the only person available to take your call would be Keith Richards and he's out back having a drink and a cigarette and you need to call back later.

If you could, which you cannot since you have mass. No matter how close you get to the speed, time remains the same for you. For you it never becomes undefined since the Lorentz factor denominator does not go to zero as it does for a massless particle.

 

[Pablo]

If you could, which you cannot since you have mass. No matter how close you get to the speed, time remains the same for you. It never becomes undefined since the Lorentz factor denominator does not go to zero as it does for a massless particle.

Plus don’t we have a lot of these threads over the years?

 

[RedSpider]

If you could, which you cannot since you have mass. No matter how close you get to the speed, time remains the same for you. It becomes undefined since the Lorentz factor denominator does not go to zero as it does for a massless particle.

You are correct. For the sake of my statement, I was assuming I had no mass.