Are Mecha a feasible alternative to tanks.

I don't think so, and I'll admit guilt in discussing this under a different post, so I figured I would move it here, although I kinda wish I had done so sooner.

Physically feasible mecha aren't made to take a RPG round to the face.

I still think you have the wrong impression of what a Mecha actually IS.

For my argument, can you explain exactly what you envision a mech to be?

Early type mechs would be useless, but technology could evolve. On the other hand, anti-mech technology would also rapidly evolve. I should have made my long ass tank v mecha post here too.

A large armored humanoid machine. Generally ranging from 4-15 meters tall, usually packing a rifle and maybe a few missiles.

Mobile suits can universally take an RPG to any point without suffering much more than needing a new paint job afterwards.
Veritech's vary from design to design on whether or not they can take an RPG but generally no they can't.
Super robots can generally take plot based amounts of damage, sometimes they get trashed quick other times they are invincible, but those are like superheroes in that way.
Knightmares can take anything up to a 90mm cannon, at least that's the impression I got from what I watched, after that point they start taking damage, those are realistic but not viable since an abrams can take a 120 mm on the front hull or turret and be basically unharmed (yes that thing is so stupifyingly heavily armored it cannot hurt itself in the places it will generally let you see.) and they can move about the same speed, except the lancelot which is a supermech if I ever saw one.
Armor Core mechs also vary but those things are freaking huge and a 110mm cannon is a machine gun to those things.
Battletech mechs are horrible I don't know why they use them.
40k mechs aren't too much better, then again 40k tech in general sucks, modern humans would crush them horribly. The only vehicles I see as being viable here are the Tau Empire Battlesuits, those things kick ass, but are classified as powered armor not mecha, despite them functioning like mecha(you sit in a cockpit and you command the thing with your brain like you would your own body, funny stories abound about this)
The FMP Arm Slaves are truly impressive machines but they are still really big and fall apart kinda easy, since they attempt to use real world physics.
The Blue Gender Armored Shrikes suck noodle, specifically in the department of firepower, guns of that caliber should blow through anything but the most stout of force fields.
Oddly enough The Big Guy from Fox's Big Guy and Rusty was a truly horrifying piece of machinery mostly due to the amount of firepower the thing had (15 feet 4 machine guns at least 6 missile launchers and, I think, 2 plasma cannons, laser beams in its eyes.)
Evangelion units were powerful but dangerous to everyone including the pilots, there weren't very many, and they came with the horrifying realization that everyone is going to be turned into orange goo.

There are others but I'm not gonna list them all. The point is that mechs are not viable because of the same reason tanks are so short, and that is anything that is over a certain height will get hammered down on a modern battle field, Helicopters and Planes are fine because helicopters carry so much firepower no one wants to go near them and they can fly stupifyingly fast for vehicles which use propellers, and are immune to small arms fire unless you hit the hardest part on the entire vehicle, the rotor connecting the rest of the vehicle to the propeller, if they have a good pilot they can dodge RPGs, and planes are nothing but speed and guns two things I suggest ever war machine have.
Tanks get to continue on for the next few decades because they are handy for when you need to slug it out with anyone, I'm not entirely sure of the tanks future either the bloody things are expensive and hard to maintain compared to other vehicles plus they are expensive and hard to transport because of their weight.

/text wall

Wow, when/if we become able of traveling at speeds faster than or equal to light (doubtful), atmospheric deprivation weapons will ensure one hell of a MAD policy (MAD=Mutually Assured Destruction).

The problem with tiny weapons such as bacteria and nanites is the same problem with all weapons, in that weapons and defenses against said weapons will always evolve on par with each other, for example, the missiles are prone to being shot out of the sky by other missiles so they are viable if you throw enough of them at the problem. That's just an example, nanites which deliver death will run into anti-nanites or force fields or some other form of mechanism which will prevent them from acquiring their targets, probably all of the above though, using technology like nanites is extremely difficult, unless you are the only one making them, which isn't likely. History has proven time and time again that the sword scales up at the same speed as the shield, with the odd exception of the invention of the gun, something we haven't been able to defend against, unless with more gun, until modern times even then we haven't gotten it quite right.

EDIT: when you gain faster than light travel the best weapon for destroying your enemy is to grab a big solid rock and take it with you when you go FTL and hit the target with the rock, well ok it's not the best but it is the most cost efficient for death/price ratio.

I think we have found ways to stop bullets fired from handheld weapons, its just that we don't have any effective means that can be deployed as body armor for troops, and I don't suspect we will for some time. I am thankful for body armor though.

I did say we haven't developed anything, until recently, in the last 10 years we have developed and mass-produced armor which will stop almost every weapon infantry will have, 50 cal. and anti-tank weapons being the exceptions. Modern American infantry wear armor which will stop most bullets that hit it. Too bad that a better suit of armor showed up right after they finished buying the IBA (interceptor battle armor), by the name of Dragon skin, which is debatable but that is for another thread.

EDIT: Key word: until recently. Take note of it.

I knew about Dragon Skin, I used it for an idea for power armor substitutes in the "Which country will have the first mech" thread.

And for the concept of using the rock as a weapon, it would all depend on the principles on which the FTL system works. If it is like in Mass Effect, then yes, because of the ability to make the rock super light as well. If it were based on something like the Shaw-Fujikawa trans light engine from Halo, the rock would have to be secured onto the outside hull of the ship and would not survive the transfer into or out of FTL space. So in the right circumstances of FTL travel, I'd agree. A rock would be the best choice for cost-effectiveness

You go to /k/?

Fair enough, things did tend to come out of a Shaw-Fujikawa drive at the same speed as the went in, but most types of FTL would allow for rocks to be flung at planets at speed, with Shaw-Fujikawa you only get the maximum speed the rock attained after being dropped/hurled from the ship, which is still not superluminal (Faster than light but sounds cooler.)

Agreed. I still think atmospheric deprivation weapons would be crazy just to see. The planet's surface temp rises by thousands of degrees in minutes. Anyway, back to mechs

The only mech I can imagine being effective is a tank turret on a four-legged chassis that can affix itself in the ground to be both a stationary firing platform, an all-terrain platform, and able to scale obstacles, but it would be too slow with hydraulic fluids powering joint movement and synthetic muscles seem a long ways off

Grav tanks are more efficient, they basically fly though. Only real advantage a walker tank, over modern tanks anyhow, would have, is the ability to get over certain obstacles, and those are so rare that it's not even worth developing that kind of vehicle.
Atmospheric deprivation tech only works if you want to kill any world under certain tech levels, for example if they were the same tech level as you, you would have to fight them for it first, or if they were of a lower tech level yet still had a fleet in space you would still have to fight them unless you fought dirty, you would also have to possess no desire to own that planet yourself, since it will be to inconvenient to inhabit a planet with no atmosphere, you could still mine it I suppose but you might as well go somewhere else for that, somewhere with an atmosphere or less gravity.

Put this way, given slightly more advanced technology.

One of the reasons why gundams were used in the series was due to the mobility advantage they had. They towered over the battlefield, being able to spot enemies from long distance, and have 360 x,y-axis movement and Z-axis sight as well. Technology also allows gundams to be fast on the field to dodge shells and missiles and gundams house complex sensors in its circuitry. I'm refering to Gundam 08th MS Team where the series was completely land-based combat. Gundams can also fly on hover/jet-propulsion systems.

Now, Full Metal Panic features why ASs (Armored slave) are the edge in warfare. Tanks are too slow to move and operate while you have greenbacks jumping from one place to another, shooting bullets that can penetrate any type of armored vechicle. (I'm not going to refer to the ECS and lambda drive because that's way out of our league.)

Varitech fighters are also viable due to their mobility. Having air superiority is sometimes very key in battles, due to the fact that ground forces usually don't have the right firepower or equipment to shoot down jets. The F-14 Tomcat is a great invention, able to fold back wings to achieve mach 3+ speed while unfolding for superior air dogfighting maneuverability. Cross that with the ability to take the fight to the ground, and they are the ultimate armor/backup support. Think of Kiss Dum Engage Planet (the shitty anime it was for bad plot but great animation) and the way the jet can split into a ground-based fighter is a great and useful concept. Also reminds me of the viking unit from Starcraft II. (Once I get that game, and I play Terran, those Vikings are going to make a difference in combat for sure - they're goliaths, but better.)

Now, all this technology is supposedly too advanced for us now. I remember someone mentioning the cumbersome weight and clumsiness of a bipedal robot. I agree with that, and something like a quadruple-legged robot would be more practical, since it has the ability to traverse any type of terrain at the cost of speed but increased mobility. I keep thinking of dragoons and immortals from Starcraft I & II, and having something like that on the battlefield would be awesome in my opinion.

mech for a tank? for me it's a bit different it's like a giant Armor to protect the body with high powered weapons

The problem with gundams is that the tech being used by them was typically 100+ years in advance of the tanks that were in the show, remember if you can see your opponent your opponent can see you if you are using the same tech level. Oh, yeah and the laws of physics wouldn't allow anything that big or heavy to move that fast without being aerodynamic, it would simply shake apart, after bursting into flames.

Yea yea, hence the warning tag in post saying "in the future."

Though bipedal robots aren't impossible, and something like the goliath from Starcraft looks very viable to me.

No, I meant the tanks in the show were basically British MK 1s wandering around modern battle fields, so of course they sucked. I'm well aware that mechs aren't viable now, we haven't developed them enough.